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Hi all, found this little gem of a forum after trolling the internet for some answers. Seems like a lot of smart people (smarter than me at least) here, so thought I would pick ya'll brains.

A little background. I am installing a Painless (oxymoron) 10150 Direct Fit Harness to my California 1984 CJ7, plus installing a Howell TBI kit, with a MSD Street Fire CDI. There are some issues that need to be clarified to me, and may benefit others too. So I will expose my ineptness for the benefit for all. I will limit this to one pressing question for now.

Per Howell instructions-"After the grounds are secured, route the labeled purple and orange wires to the starter solenoid on the right hand fender well or to the starter. These wires each have a lug that attaches to the stud on either side of the solenoid or starter. (FIGURE 11) The orange wire is battery power and connects on the battery side of the solenoid or the positive post of the starter. The purple wire connects on the opposite side of the solenoid or to the starter solenoid post of the starter. Connect the labeled white wire to the ignition coil negative terminal to pick up a tach signal. NOTE: Multiple spark discharge ignitions require a special tach filter to function correctly. Contact Howell Engine Developments if you need one."

So the inept question time.  I have a Multi spark ignition. I am attaching the Howell Orange and Purple wires to solenoid per instructions if that matters.

However, should I purchase the special tach filter (as recommended by Howell) to connect the tach signal for the ECM from the CDI, or can I just connect the WHITE WIRE to the negative (-) terminal of the coil and be golden (or is that a bad idea)? If coil connection is ok, is there a benefit to connecting to the CDI over the coil? The only thing I can think of that may be an issue attaching to the coil is the 430 volts the MSD is sending to the coil and that being an issue! Kinda thinking the coil connection is a bad idea with this CDI (or any CDI).

Thank you.......

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Please share, Nucking Futs...I was going to suggest that you take an actual voltage meter reading at the negative 12V coil lead (primary posts).  

With an MSD AL6 box, I have used an MSD tach filter on a breaker point ignition for a vintage Jeep 4-cylinder application.

Let us know your "fix", and thanks for joining us at the forums!

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  • 2 weeks later...

Sorry for the delay, several home projects that needed my dire attention. 

My fix was to directly connect the ECM to the tach signal from the MSD Street Fire CDI. I looked around the internet, and several people just connected the ECM to the tach signal from the CDI. Seems to be working so far. Idle is high (900 +/-), but I may need to adjust that per Howells instructions. I have about 30 miles on her so far, so maybe the computer is still learning?? 

I might decide to purchase the filter, just in case. I would rather be proactive than reactive. I just need to get a GM air cleaner assembly for the junkyard to "look smog legal" versus the open air element that Howell suggest. That will just tweak the smog techs, as the TBI conversion won't tweak them already. Again, proactive approach.

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Some of Howell's systems do have a California E.O. number, they are legal if you have the crankcase closed as required, which can include a return draw to the air cleaner and PCV.  The Howell E.O. instructions indicate the required equipment for meeting the California C.A.R.B. requirements for this system.  You're right, the visual inspection is a sure way to pass or fail, and the air cleaner needs to function as intended.

As for signaling off the ECM, my only concern would be resistance or possible damage to the ECM.  You share that others have been successful with this approach.  I'm leaning toward your reasoning and the use of the filter.

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The Air cleaner is usually the killer in visual inspection. Ironically, the California approved E.O. kit from Howell suggest an open element, which is approved by California! Its all about money and Howell paid Ca for the E.O. (proof our laws are about money and not environmental). 

Now I do have a question about idle. Disclaimer, I am at best a weekend mechanic, at that is a stretch. My Jeep wants to idle around 900-1000 RPM, and when it sits for a minute will drop down to 750-800 gradually. To me it is acting like a vacuum leak, but I have no idle change with a propane test around TBI base, vacuum ports, hoses, PCV, CTO.  There is no CE light, and I have no error codes. I am not convinced yet that I do not have a vacuum leak.

But, wouldn't a slight vacuum leak set off a code? I am concerned that I may have a slight leak though the adapter plate, which needed silicone to fill over the bolts. The plenum cuts into the cavity of the bolt heads just a little, and Howell instructions inform that the heads need to be sealed with silicone to prevent a leak.This is my initial feeling, but have not confirmed it yet.

Jeep idles around 900 rpm and is smooth, drives down the road great. When it does idle down to the 750-800 range, it does get just a little rough on idle, not much, it is just noticeable. Things I have not checked yet include: plugs/wires, manifold/ported vacuum at idle and speed, fuel pressure (in/out), voltage at ECM at idle. I did check timing and retard to Howells recommended 6 to 8 degrees with no vacuum hose attached to distributor and blocked off while setting. Distributor gets ported vacuum. It would be nice to check total timing if I had the right tools.

Anything else I should be looking at before I adjust the idle stop? I want to make sure I am not masking the problem(s).  

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Of course Howell would be the final say in engine tune and performance, but this is essentially a G.M. 4.3L Vortec V-6 TBI system.  I would troubleshoot your symptoms using a G.M. service guide for the 4.3L Vortec V-6 with TBI.  It sounds like an idle air control (IAC) issue, but if so you want to know what is triggering this problem, the devices involved and the signals to the ECM that affect idle air control or IAC functions.  

Troubleshoot the devices and also check for a manifold leak.  You can do this quickly with a can of WD-40 or a similar low volatility spray.  (Avoid spraying near heat or the exhaust manifold.)  Spray a light mist at the manifold/TBI junction with the engine at a idle.  Listen for any brief, simultaneous engine speed change.

Fuel pressure is always a place to start with EFI trouble, and the coolant temp, air intake temp and MAP signals are important, too.  Each can influence idle, but I would begin with a focus on the IAC triggers.

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I disconnected the IAC and ran the engine under load. Idle ran back up to 900-1000 again. Also heard a faint whistle sound. Vacuum leak through the TB somewhere, just haven't found it yet. The good news it is not the IAC pintle, EGR, MAP, and it is just a vacuum leak (most likely). 

Most likely place is the adapter plate. I will try some WD40 or carb cleaner this time instead of propane. 

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Latest update: EGR is bad. While that steadied the idle, still running a little high at times. Haven't gone down to get a gauge to check pressure, do that this weekend.

But, the funny thing. If I coast down the road at any given speed (clutch in and/or out of gear), she will idle around 1000 rpm. If I stop, idles down to 800 rpm +/-. If I sit still, idle will come done to 750 rpm. What the heck? Emailed Howell and I have yet to receive a reply. Phone call next.

I am new to TBI and ECM in general. To me, it is a programming issue, or speed sensor issue. I just cannot find a vacuum leak to explain the idle, nor should it vary with speed anyways. Or is there something else that could cause a fluctuation in idle according to speed?

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Nucking Futs...Yea, now you're getting somewhere with the EGR!  Does this system use a vehicle speed sensor?  The Jeep MPI conversion kit does, as the Jeep PCM relies on the vehicle speed signal for some EFI functions.  Does Howell use a VSS on the TBI conversion?  I'm not aware of it.

Check for a possible vacuum leak, including a leak between the intake manifold and cylinder head.  That gasket or your TBI-to-intake manifold could be involved.  Going down the road does affect the underhood atmospheric pressure.  Is the MAP sensor okay?  

This idle speed problem could also be unrelated to the TBI system.  You have the MSD ignition enhancement.  Does this adjust spark timing in any way or does it just enhance spark output?  If you're still using the OEM Motorcraft distributor, make sure your distributor vacuum canister is fed ported vacuum and not manifold vacuum.  Also make sure that the distributor's mechanical advance mechanism is not sticking, making it unable to smoothly and accurately retard spark timing as the engine speed drops.  A sticky centrifugal advance would hold the idle high. 

Take your timing light and watch the spark timing as the engine holds the higher rpm at an idle.  Watch the timing as the speed drops off...You could have a sticky centrifugal spark advance mechanism in the distributor, or the vacuum source for the vacuum advance might be hooked up to manifold vacuum instead of ported.  

Note: On your TBI conversion system, you can bypass the maze of 4.2L OEM spark advance/retard solenoids activated by the factory ECU.  (You can leave these devices on the chassis, but they no longer serve a purpose with the Howell TBI installed.)  Simply run a vacuum hose directly from the TBI ported vacuum to the distributor's vacuum canister...Check with a gauge to confirm that the vacuum source is ported and not manifold vacuum.  (Ported vacuum should read close to zero in/hg with the throttle valve closed.)  The TBI unit has a ported vacuum port and possibly a manifold vacuum source.  Cap off the manifold vacuum source.

There is a CTO (a coolant temperature vacuum interrupter switch) in the distributor's vacuum circuit.  This is also used for the EGR vacuum circuit.  This prevents vacuum spark advance and EGR operation until the engine reaches normal operating temperature.  I'm not sure whether Howell requires this to meet emissions standards.  If not, you can run a direct hose from the TBI ported vacuum source to the distributor's vacuum canister or run this hose via the CTO.

Be aware that EGR is also opened with ported vacuum and not manifold vacuum.  If hooked to manifold vacuum, the EGR would remain open whenever the engine is running.  The EGR valve is not supposed to open at a close throttle position or when ported vacuum drops off.  Make sure your EGR valve has a ported vacuum source.

Moses

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  • 3 years later...

Hi, it has been a minute since I've reported in. I've been wrestling with little things in life and the Jeep.

Update, I found a few very small vacuum leaks, but I always suspected a major issue(s). Disconnecting all vacuum sources and still have a slight issue with higher idle. I noticed that I had major blow by one day (engine compartment had an oil bath which is a long story) when I removed the PCV system to see what would happen. It was pretty bad how much oil came out of and around the dip-stick. Oil has a gas smell too. Looks like I lost some rings.

While I am not sure, I suspect this was causing issues with the MAP sensor. Just a guess at this point. My engine has issues and need a rebuild. A little sad at 170,xxx miles (assuming it is correct).

This is outside of my wheelhouse currently, so I need to pay a professional to have my engine rebuilt. Now, I just want a little more HP on the top end without sacrificing the torque at the low end. I need to find a good builder to square this engine for me. 

 

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Nucking Futs...Unless the engine has been burning oil, indicated by an ongoing drop in oil level and possible oil fouling of the spark plugs, I would do some tests before rebuilding the engine.  My first step would be a cylinder leakdown test on each cylinder with its piston at TDC on the compression stroke (both valves closed). 

There are pinpoint wave form readings you can observe with a lab scope and in-cylinder pressure transducer tests; however, you would need a lab scope and pressure transducer kit to do so.  An OTC or equivalent leakdown tester would be a fraction of that cost.  Even an inexpensive compression test would be helpful though nowhere near as revealing as a leakdown test.  Here's the best buy I could find on an OTC leakdown tester, you may be able to beat it:

https://www.tooldiscounter.com/product/otc-cylinder-leakage-tester-kit-otc5609

The combination of an engine running manifold vacuum gauge reading and a full six-cylinder leakdown test is the closest thing to disassembling the engine for inspection.  One added step would be an in-cylinder camera, I picked one up for $60 at Costco years back, they are available from a variety of sources.  Make sure the camera's sleeve will fit through the spark plug hole diameters on your engine(s.) 

When I look inside the cylinders with a camera before considering a rebuild, my focus is the amount of upper cylinder wear or cylinder "taper".  This indicates how far the rebuild will go and whether there will be a demand for re-boring the cylinders.  You're looking at $1800 or so for complete machining and customary parts renewal to fully recondition a 4.2L AMC/Jeep® inline six-cylinder engine.

To put this in perspective, 170K miles on an engine with the stroke length of the 4.2L is a great deal of piston travel (also governed by axle gearing and tire diameter, overdrive transmission, etc.).  This is not a Toyota 300K Club engine although the Toyota FJ40 inline six had a long stroke and similar piston travel issues.  I lacerated my fingers handling a 2F engine's piston rings.  They were razor sharp at the edges due to plenty of piston travel and a harder, higher nickel content cylinder block, much more wear resistant than an AMC engine.  That FJ40 100K engine did not need reboring but did require stone cylinder honing and new piston rings.

So, you may conclude that the engine is tired enough for the rebuild.  My focus with the idle fluctuations would be manifold vacuum to the MAP sensor or exhaust back pressure, which we may not have considered.  A bad or clogged cat, muffler or other exhaust restrictions can cause idle issues.  A simple test is an infrared scan of the exhaust system temp from each manifold port at the cylinder head through the cat, muffler and tailpipe.  A surface gun test or FLIR test with an iPhone is the least expensive way to do a trace for heat and heat void clogs.  An infrared surface thermometer is $20-$60.

Moses

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Hi Moses, thank you for the sage advice. I agree that a leakdown test will be the most telling. I have no abnormal oil consumption, but oil has an excessive gas smell. Yes, I will be doing (or employe my mechanic) to do a leakdown test. I have considered back-pressure to some degree. I installed a new cat when I installed my Howell system as I did not know the age of the catalytic converter and wanted to remove that variable just in case it had issues. 30-years ago, I had an old 70's Monte Carlo that the cat was plugged. It would not run. I have not looked at the muffler and it could be causing excessive restriction. I will look into that.

I did hook up my desktop to the Howell ECM. I was never able to save the engine log, it would not allow me to access. However, I recall everything looked within range, but I did not test the actual TPS. 

Leakdown test, bore scope cylinders, muffler flow, and some further testing of components will be down before a rebuild. I shall report back when I have more information. 

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Nucking Futs...Sounds thorough...Let us know what you discover.  Might be sensible to do another PC read of the Howell ECM. 

Look at fuel trim and the MAP readings.  If TPS readings are available, note the voltage at different throttle positions...Fuel trim will indicate the O2 sensor behavior and the air/fuel ratios required to keep the engine running in balance or stoichiometric.  In trying to separate issues, it would be good to know whether the engine is running rich, possibly the source for the fuel smell in the crankcase.

Beyond this, the rest of the story should be in the leakdown test and bore scope view...

Moses

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I was quoted $350-400 for leak-down test. Wow,  that is $400 that can go to a rebuild. Does not make economical sense right now. So, I did my own compression test with a Harbor Freight (HF) compression test gauge I bought. Not sure if numbers are accurate (either the gauge or the tool working the gauge).

1-160psi

2-135psi

3-150psi

4-140psi

5-125psi

6-160psi

#1 and #6 numbers are above the service manual listed specs for cylinder compression. Also, the cylinders next to the higher ones are lower. The service manual states 120-150 psi and no greater than 30psi between cylinders. I am outside of spec for both. Could I have a cylinder to cylinder compression leak? If so, then my head needs work (the jeep's head that is). No oil consumption only blow-by, no water in oil, no oil in water. 

I will be looking to see if HF or some other manufacturer makes a cheapo kit for leak-down testing. Or maybe I can make my own if it is not too prohibitive or costly. For the right price, it is worth investigating. Odds are I need to pull the head, so $400 to test for leak is $400 that will go for the cylinder head work.

Or maybe a good time for a 4.0L head swap......that could be fun. More to come.

 

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Nucking Futs...I checked, and Harbor Freight has a clearance price on an occasional use leak down tester ($25).  If you have an air compressor (not a large tank required), this is a smoking deal and will work:

https://www.harborfreight.com/cylinder-leak-down-tester-62595.html

My philosophy is to buy tools instead of others' shop labor.  Considering the labor charge estimated for a leak down test on a simpler, inline six-cylinder pushrod engine, I'm in the wrong business.  The task takes 60-90 minutes at the most.  Even at $120 per hour labor rate and the full 90 minutes, that's $180.  $400?

The only effort here is removal of the spark plugs and running each piston to TDC on its compression stroke.  With the valves closed and piston at TDC, the cylinder can be accurately tested for leak down.  Throw the $25 at the HF leak down tester before they're all gone.  Reviews are not great, but one thing that helps is to run a minimum of 60 PSI air pressure through the gauge.  If you want to step up, OTC's leak down tester is around $65 at Summit Racing and Amazon. 

I run my Snap-On tester at 90-110 PSI air system pressure.  The Snap-On tester calls for 60 PSI line pressure setting.  If you run higher, you will get better piston ring seal and a somewhat normal representation of a running engine.  Experiment with the incoming line pressure setting.  The HF tool should work, but if the unit is a bust, HF has a wonderful return policy.

From the cranking compression test (throttle should be wide open during test), you have a spread of 35 PSI between the two high cylinders and the lowest reading at #5 cylinder.  160 is actually a bit high and likely carbon buildup.  125 is at the low end of acceptable but still quite functional.  "Normal" is 120-150 PSI.

The issue is the PSI spread for cylinder balance.  Ideally, I like to see no more than 10% difference between the highest and lowest cylinder.  (AMC/Jeep allows 30 PSI.)  You have nearly 22%, which is not far from AMC's approximate 20%.  I will comment more after you perform the leak down test, but I am leaning toward the need for a valve grind and de-carbonizing the piston crowns and combustion chambers.  Pinpoint where any air is leaking (intake valve, exhaust valve, past the rings or head gasket seepage).  Frankly, this engine is not in bad shape for the mileage.

Run #5 piston to TDC.  You can pinpoint whether you're on the compression stroke by removing the distributor cap and seeing whether the rotor points at #5 cylinder.  Be certain the piston is at its peak to prevent the leak down air pressure from forcing the piston downward.  With both valves closed and the piston at TDC, you will learn a lot.

Let's discuss your findings from the leak down test.  For the record, cranking compression tests can be highly misleading.

Moses

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Great advice Moses. Yeah, $400 was crazy. For a 90 min test, that is 😮!

I did not have the throttle open and not sure how much that will impact the readings. No issues redoing the test as it is pretty easy. 

I have a 30-gal 200-psi compressor so good to go there. If I buy a tool, i subscribe to the philosophy Buy once-Cry once. I saw the HF on clearance for $25. I will leave that for those who have a tighter budget. I saw the OTC gauge and looks satisfactory for my shade tree work. 

I will rerun the compression test and report on the leak down when my gauge arrives. In the meantime I will be searching for a quality machine shop (not the previously mentions place). 

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  • Moses Ludel changed the title to Estimating 4.2L Jeep CJ Engine Condition with Howell TBI
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Good, plan...You can narrow the compression check to #5 cylinder.  The leak down test will be far more conclusive. 

OTC's gauge is popular.  Looking forward to your leak down results.  Use the OTC guidelines/PSI settings for openers...Go from there.

I added some info to my last reply.  Look over my reply, there may be some new comments...

Moses

 

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I did the compression test again, this time with throttle open and original numbers had errors from that. Also, my HF gauge and the supplied adapters will not thread into head. I had to use the tapered rubber tube. I verified what will give me the correct angle to help insure a proper seal.  

New:1-155  /  Old:1-160

New:2-157  /  Old:2-135

New:3-165  /  Old:3-150

New:4-150  /  Old:4-140

 New:5-180  /  Old:5-125

 New:6-165  /  Old6-160

Assuming the gauge has a 5-10% error, numbers a pretty good, if not great, for a 170,000 mile 258 (sans #5). If the gauge numbers are correct, that is a little high for a Jeep with 170,000 miles. I will preform the leak down test when kit arrives. All in all, this is interesting stuff to me. I hope others can learn form this.

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Wow, this made a significant difference...The new numbers, if they line up with the leak down test results, indicate an engine with carbon buildup.  A compression test requires available air.  With the throttle closed, the intake air volume is often too small to fill the cylinders properly at cranking speed.  The jump in compression proved that with your open throttle test.

The #5 cylinder reveals considerable carbon buildup on the piston crowns, combustion chambers and valves.  So far, there's nothing conclusive about the piston ring seal; however, it appears that the rings are sealing from your readings. 

My diagnostic goal would be leak down results and determining the degree of taper in the cylinders.  One way to test taper, without a bore scope or cylinder head removal, is to first run the leak down test at TDC.  Then run a leak down test on the same cylinder with the piston dropping down an inch to two inches in the cylinder (past TDC)This is tricky because the piston will want to move downward when you apply compressed air with the leak down tester.  Leave the other five spark plugs in place.  This will help resist crankshaft rotation.

If the leak percentage decreases noticeably with the piston lower in the cylinder and both valves still closed, this indicates that the rings are sealing better.  That, in turn, suggests that there is taper/wear near the top of the piston ring travel in the cylinder.  This test technique can prove insightful.  

Another path that I've taken in recent years is an inexpensive bore scope/camera with a small enough probe end to reach through the 14mm spark hole.  HF, Amazon, Summit Racing and others sell these cameras for around $60-$75.  The camera probe end is small enough to fit through a spark plug hole, and the camera will work within a dark cylinder.  I bought mine at Costco of all places, correct size for automotive engine work.  The camera showed up there and sold out at $59.  I haven't seen it there since.  Here's the HF Cen-Tech unit that gets good reviews.  I am not suggesting that you need a bore scope/camera:

https://www.harborfreight.com/digital-inspection-camera-61839.html

The bore scope works by lowering the piston and observing/filming the cylinder wear before engine tear down.  Lowering the piston exposes the best view of the piston ring travel area of the cylinder, the amount of wall taper, valve condition, carbon buildup and any scoring of the cylinder wall(s).  This has helped me plan and estimate cost on engine rebuilds by pinpointing their machining needs before a complete tear down.  

You'll be pleased with the diagnostic value and insight your leak down tester will provide.  Looking forward to your findings!

Meanwhile, if you have a vacuum gauge, I'd like to know what kind of manifold vacuum this engine produces at a warmed idle.  Manifold vacuum is read below the carburetor at a port on the intake manifold.  In/hg would be useful for determining timing chain wear.  I can share another technique if you don't have a vacuum gauge.  Also, what is the warmed oil pressure?

Moses

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Thanks for the great feedback Moses, I do appreciate it. To further your hypotenuse of carbon build up, I have to run 91 octane even on the flat land at 8* timing or she'll spark knock so those numbers may be pretty close. Driving up I-80 or Hwy-50 over the Sierra Nevadas is a slow drive. 

Running the leakdown will be an educational experience. I do believe it will reveal that the head needs to come off for cleaning and inspection. We shall see what it reveals.

I do have a vacuum gauge (HF). It works, but it does not reset to zero. Easily replaced, they are not too expensive. I have checked the vacuum before. When I bought the Jeep, there was a dip in vacuum every now and then along with a ticking sound from the 5-6 cylinder area. I changed my oil, put some good ole Mystery Oil in, some Lucas Fuel treatment in the gas tank, and changed my oil every month for about 6-month, along with a little water down the carb (pre-TBI) to steam clean the cylinder. It was recommended to me and I was told it was safe as long as I use a small amount of water. This was a while ago. The ticking and vacuum drop has pretty much disappeared after , though the ticking has started once again.

Oil pressure, well the gauge stopped working 2-month ago. Before it quit, warm idle was around 40psi +/-. 

 

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  • Moses Ludel changed the title to Estimating 4.2L Jeep CJ Engine Condition and Tune with Howell TBI
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Nucking Futs...I'm optimistic about where this is headed...The leakdown test will be revealing and pinpoint what the engine needs.

The 4.2L cylinder head has a propensity for ping/detonation.  This was the result of emissions demands, ignition timing requirements, the long stroke and combustion chamber design.  The combustion chamber design led to the much improved 4.0L (1991-up MPI version) cylinder head redesign.  These later engines do not require a knock sensor, and the engines will tolerate 87-88 octane fuel—at least at my 4,400-foot elevation east of the Sierra region.  At sea level, higher octane fuel may be required due to the higher compression realized at sea level atmospheric pressure.  

Another point worth emphasizing is that the Mopar EFI Conversion recommended 91-92 octane fuel.  This is because the system was essentially off the shelf 1995 YJ Wrangler 4.0L design.  A 1991-95 Wrangler 4.0L engine had a better combustion chamber and port design than the 4.2L.  The "bolt-on" EFI conversion did lead to ping/detonation on the target 1981-90 4.2L AMC/Jeep inline six.  Similarly, you also have an emission legal EFI conversion, so detonation/ping is not surprising.  Ping can, however, be reduced or eliminated.

Aside from the carbon buildup factor, which as you suggest is a major contributor to ping/detonation, you are running the somewhat high base timing spark advance for a 4.2L AMC/Jeep inline six.  The original ignition and tune system had a built-in spark retard, which you likely have bypassed with the Howell EFI.  You also have the MSD ignition upgrade. 

Is your distributor the original Motorcraft with its stock timing advance curves (centrifugal and vacuum)?  Stock base spark timing was 9  +/-  2 degrees BTDC, according to the 1984 AMC/Jeep FSM.  This base timing is set with the vacuum hose disconnected from the vacuum canister and taped off during the timing light check at idle.  The factory timing reflects the emissions spark retard/override of distributor timing, which may no longer be operative after the Howell kit and clean-up that follows.  You may have too much spark advance over the entire range of timing.

8 degrees BTDC could be too much advance for your engine's design to handle.  (Without the carbon buildup and excessive compression, that might change.)  If the advance curve is stock and the vacuum advance is hooked to ported vacuum, you have latitude to retard the base idle timing.  Make certain that the vacuum advance canister is sourcing vacuum from ported vacuum and not manifold vacuum

See my next reply for OEM spark timing curves that AMC/Jeep recommended...There were years when the factory base timing was 2-4 degree BTDC on these engines.  1981-90 picked up the base timing in accord with the Motorcraft SSI distributor and an emissions package that includes the electronic MCU for controlling spark timing retard as one of the emissions functions. 

Moses

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  • Moses Ludel changed the title to Evaluating 4.2L Jeep CJ Engine Condition and Tune with Howell TBI

Point of correction from last message. I stated "hypotenuse". It should have been "hypothesis". My bad, but I am working on 30 min of sleep in the last 48 hours. Power nap coming.

Wow, lots of good stuff here. I was not aware of the ping issues as a whole for the 4.2L. The worn out emissions components from the factory labored it horribly, hence the Howell TBI. The Mopar MPI was just too pricey. 

I currently have the stock distributor and went back to the Dura-Spark module. I could not find my CARB sticker for the MSD, so had to switch back for emisions testing. I'm not getting all that advance through mechanical, vacuum, or both. I know the dizzy has issues. I am running and have verified that ported vacuum is going into the dizzy-vacuum canister.  As per timing at 8 degrees. Howell instructions state 6-8*. The engine for the most part around town likes the 8* for my overall DD. That would have to change for a mountain run. I will try 6* and see how that goes. I would love to put a D.U.I. HEI on her to simplify the engine compartment even more. 

Of somewhat concerning is if I try 4* I can get backfiring through the TBI. I think that is an indication that I have a little too much stretch in the timing chain and may have jumped a little. At 170,000 miles with issues, it is definitely time to replace before a catastrophic failure happens.  

Dang Moses, the more I dig into her.......She runs pretty good, smog emission numbers are very good! Low RPM is okay, not like it use to be after the nutter bypass and before Howell TBI. Mid power is okay, good enough to scoot down the Interstate. I will see what I can do with the leakdown test. 

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Nucking Futs...I figured so and moved past the comment, thinking you were not referring to geometry.  Lack of sleep will do it!

The leakdown test will be revealing.  Percentages are a clear reflection of piston ring seal, valve seating, casting cracks or warp, cylinder taper and gasket integrity.  If the leak percentage is reasonable, you have a carbon buildup that could be resolved with head removal. 

If on a tight budget, you could carefully remove the valve springs, laying out parts in sequence, inspect the valves and seats, check the valve stem-to-guide clearance and decide whether to sublet the head for surfacing and valve grinding.  If wear is negligible and savings paramount, you could remove all carbon, and if valve seat margins are not too wide, you could lap the valves, install new valve guide seals and install the head with new gaskets.

While the head is off, the crown of each piston at TDC can be de-carbonized carefully with a powered wire brush (wear your mask) of the correct abrasive level or wire size.  Debris can be cleaned away with a shop vacuum, focusing on the piston to wall gap.  The cylinder wall taper would be checked.

I'm getting ahead of it and being optimistic.  The key concern is piston ring seal and cylinder taper.  It is not wise to do a valve grind on an engine with weak rings and excessive cylinder taper.  One step at a time, beginning with your leakdown test.

Moses

 

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Less sleep deprived now. Leakdown kit it should be here tomorrow, but I imagine it will be Saturday before I can get some numbers. 

The budget, well I am always looking so save where I can but a full rebuild is in the budget if needed. However, a head removal and cleaning is the best I can do in my current situation. It is not permanent, but impactful. To pull apart the head is just not in the equation currently. It is what it is. However, if conditions of valves and head determine that a full head work is needed, I will be looking for for a machine shop for block and head work. I am not doing the top half now only to do the bottom half later which would require pulling the top half off I just did. Make no sense. So if that is the case, then I will be asking some different questions concerning the 4.0L head swap. But that is getting a head of the situation.

I will review all the information you presented to me, along with me Jeep shop service manual.

Until then, thank you. More to come Saturday.

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Nucking Futs...I'm pragmatic these days.  "Wayne" and I recently walked through an in-chassis engine overhaul that "in the day" might have been an engine removal and thorough machining/rebuilding.  The results should be quite satisfactory:

 

The cost of rebuilding has gone up like everything else, and I now consider an in-chassis rebuild acceptable under given circumstances:  1) crankshaft journals still round and smooth, 2) cylinder taper minimal and still within factory tolerance, and 3) pistons either okay or replaceable at the stock or existing bore size.  The cylinder head gets sublet to grind/restore valve seat widths, guide to stem clearance and valve faces—plus decking if warranted.  If not done prior, I always have new hard steel exhaust valve seats installed on a pre-unleaded fuel engine's cylinder head.

In-chassis rebuilding means you're laying on your back (unless you have a hoist), dropping the oil pan, rolling in a new rear main seal set, rolling in new rod and main bearings, installing a timing chain kit, a new cam and lifters if needed, and confirming pushrod lengths after the head work.  In-chassis overhaul and out of chassis rebuilding/re-manufacturing are entirely different approaches as you note. 

I'm a strong advocate of sublet engine machining when required.  If you pull the engine, the block gets torn down completely and tanked, the block gets decked, the cylinders re-bored and honed, new cam bearings and freeze plugs installed, the crank gets polished or reground, rods serviced, and I have the crank/reciprocating parts balanced with the flywheel (which is resurfaced). 

Factory shop manuals (FSMs) still refer to service measures that are "in-chassis", largely because of warranty procedures.  Today, however, "crate" engine replacement is a norm for most dealerships and many DIY consumers.  If you have a good core engine, which you do, my preference is rebuilding the original engine to assure core parts integrity.

You mentioned the water method for de-carbonizing an engine, and it does work to a reasonable extent.  I ran water/methanol injector systems on carbureted engines years ago, that worked even better, especially the types with a carburetor base plate and nozzles.  Edelbrock had an inexpensive kit for years that meted water/alcohol through a vacuum line source.  Unclear whether that exists any longer.  I searched online to see the contemporary methanol injection approach and found this website/ product line with insightful information and interesting products:  https://prometh.com/

Your 4.2L is suffering the lingering carbon buildup effects of the original BBD carburetor system.  As for the 4.0L head conversion, manifold fitment needs to be addressed.  There's a coolant port modification that is well documented.  Not sure how your 4.2L manifolds can be fitted to the intake/exhaust ports and mounting studs.  You would need to do your homework;  the Howell EFI relies on use of your stock 4.2L intake manifold, and you're invested in that approach.

Moses 

 

 

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In chassis was not considered except for a head pull to clean. Maybe if there was a fixable issue with one cylinder, but not likely. If she needs disassembly then she is being pulled. That kind of work is a pain I'm not likely to consider.

First, I need to find a trust worthy machine shop to get an estimate for the machining cost on a rebuildable block/head. I've built a FE390 20 years ago. The total cost for machining and parts was about $1200 dollars then plus my time. But inflation, tools and current location will likely limit the ability to do work myself, or make it challenging at best. The cost to machine, rebuild parts, transportation to and from shop, and/or paying a shop to do the work will all be calculated. There is a tipping point between cost and convenience for everyone and we each must find our balancing point.

Looking into crate motors, really doesn't exist for a 258 (that I have found). Not really interested in giving up my original motor anyways. What options I have found for the 258/4.2L are close to the same cost for a crate stroker and I must send then my engine for them to rebuild. The shipping will eat up any savings I could have saved from ordering a crate motor and might as well keep my local machine shop employed. However, that just makes ordering a crate stroker motor a financial smarter decision. There are several options for strokers: kits you put together, short blocks, long blocks, and turn key which is an option but is mucho dinero. Again, is is about finding that balance.

To adapt a stroker and keep some of my parts, I will need a new exhaust manifold for the corresponding year of engine. the 258/4.2L exhaust manifold will not work. On a 87-90 and 91-95 block, from my research, my 4.2L aluminum intake manifold can work with slight modification to fit. However, I'm not interested in the modifying my intake. That action potentially could make the change back to 4.2L block irreversible. The availability of the 258/4.2L is not as common as they use to be and I want to keep integrity of the engine and parts to best I can. Clifford makes a carb intake for the 4.0L that I can use my TBI. Finding the balance.

There is a lot to consider. I don't want to get too far ahead but I do have to think about my options. All decisions have merits and consequences, along with unintended outcomes not foreseen. No more philosophy. Still waiting for leakdown kit which is a bummer. I was hoping it would arrive today.

My intuition tells my engine just needs a little hygiene work on the inside. I am enjoying the learning process and diagnosis procedures. There are so valuable in a disposable age. 

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We're in full agreement.  See my comments below.  My thought is that your engine is easily restored to gain more miles before you need an overhaul/rebuild or remanufacturing.  We know you have a viable, predictable core...Moses

On 4/23/2021 at 3:20 PM, Nucking Futs said:

In chassis was not considered except for a head pull to clean. Maybe if there was a fixable issue with one cylinder, but not likely. If she needs disassembly then she is being pulled. That kind of work is a pain I'm not likely to consider.

I agree.  My recent change of a rear main seal from the floor level, adding an oil pump for good measure, was a norm fifty years ago.  I've had a 9000# chassis hoist since and know the difference...If you don't need or want to roll around on a creeper, don't do it.

First, I need to find a trust worthy machine shop to get an estimate for the machining cost on a rebuildable block/head. I've built a FE390 20 years ago. The total cost for machining and parts was about $1200 dollars then plus my time. But inflation, tools and current location will likely limit the ability to do work myself, or make it challenging at best. The cost to machine, rebuild parts, transportation to and from shop, and/or paying a shop to do the work will all be calculated. There is a tipping point between cost and convenience for everyone and we each must find our balancing point.

I subscribe to Goodson Tools' mailing list and stay up on the latest machine shop tooling and technology.  Somebody gets to pay for it.  Just like dealership and independent shop labor has escalated with ADAS and other technology, machine shop charges reflect "new school" approaches to equipment. 

There has been a trend toward exchange engines over the last four decades.  However, you have a viable core, and with careful oversight, this could be the foundation for a very reliable 4.2L engine.  You also have the TBI investment, which builds on the 4.2L intake system.

Looking into crate motors, really doesn't exist for a 258 (that I have found). Not really interested in giving up my original motor anyways. What options I have found for the 258/4.2L are close to the same cost for a crate stroker and I must send then my engine for them to rebuild. The shipping will eat up any savings I could have saved from ordering a crate motor and might as well keep my local machine shop employed. However, that just makes ordering a crate stroker motor a financial smarter decision. There are several options for strokers: kits you put together, short blocks, long blocks, and turn key which is an option but is mucho dinero. Again, is is about finding that balance.

I understand the long-in-the-tooth nature of the 4.2L and crate engines.  At least two million 4.0L engines were produced, and for reman shops, this has become a cash cow much like the historic small-block Chevrolet 350 V-8.  Comparatively, there is no volume with 4.2L engines.  As for strokers, for my '99 XJ Cherokee 4.0L, a complete, out of chassis rebuild would likely include a 4.2L crankshaft or Scat stroker crankshaft.  That's easy enough when my base engine is a 4.0L.

To adapt a stroker and keep some of my parts, I will need a new exhaust manifold for the corresponding year of engine. the 258/4.2L exhaust manifold will not work. On a 87-90 and 91-95 block, from my research, my 4.2L aluminum intake manifold can work with slight modification to fit. However, I'm not interested in the modifying my intake. That action potentially could make the change back to 4.2L block irreversible. The availability of the 258/4.2L is not as common as they use to be and I want to keep integrity of the engine and parts to best I can. Clifford makes a carb intake for the 4.0L that I can use my TBI. Finding the balance.

When I installed a Mopar EFI ('95 YJ 4.0L prototype) conversion kit on a 4.2L for my CJ Rebuilder's Manual, I used the 1995 style YJ 4.0L exhaust manifold as well.  The Mopar EFI intake was essentially a stock 1995 YJ 4.0L with minor changes to mate with the 4.2L cylinder head. 

There is a lot to consider. I don't want to get too far ahead but I do have to think about my options. All decisions have merits and consequences, along with unintended outcomes not foreseen. No more philosophy. Still waiting for leakdown kit which is a bummer. I was hoping it would arrive today.

I'm an optimist about your 4.2L engine.  Relatively minor work could net more mileage from this engine.  That would provide a larger time horizon to consider options.

My intuition tells my engine just needs a little hygiene work on the inside. I am enjoying the learning process and diagnosis procedures. There are so valuable in a disposable age.

Agreed.  We could purchase a new vehicle but haven't had a vehicle payment for more than a dozen years.  Every mile driven is a cost savings.  Each of our vehicles has accrued more than 180K miles on its odometer.  I am a strong proponent of preventive care and making repairs before things break.  This comes from my early work as a light and medium duty truck fleet mechanic.  I perform all service work on our vehicles and have saved a small fortune, some of which, logically, has been reinvested in necessary tools and equipment.  I am pleased, as you suggest, with not throwing restorable machinery away but rather rebuilding and maintaining it. 

I'm looking forward to your leakdown test findings, something that can lead to informed choices...

 

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Well, kit showed up but with no adapters and the hose will not fit into the cylinder. The threaded end is too short and it will not engage the spark plug threads. No adapters available. I cold spend my time trying to find/make and adapter, but may not work. Returned kit.

I looked at others on the web and they all look the same, short threaded section. One appeared to have long enough threads, but will not ship until mid-May. I could spend top dollar for a professional kit. But all these options are beginning to the hit the extreme ends to me. Too cheap, too expensive, or too long of a wait. This brings me to a cross roads. I can go to Harbor Freight and see if their units have long enough threads to engage so I can start the diagnostic process now. Or just pull the head, clean and inspect, which is probably what I will end up doing anyways. My pressures are goodish.

I am going to see if the HF kit threads are long enough to work. If not I will start pulling the head to be done with it and move on. The saga continues...

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I like the Harbor Freight approach...Disappointing about OTC, these tools sell everywhere.  Must be others who have encountered that issue, too.

HF tool may do the trick...All this tool needs to do is pressurize the cylinder and read the percentage of air that bleeds off.  You'll listen for noise at the tailpipe (exhaust valve leak), intake (intake valve leak) and the oil fill cap or dipstick tube (piston ring blow-by through the crankcase).  You look for bubbles in the cooling system if you suspect a blown head gasket or casting crack like an exhaust valve seat (no reason to suspect this).

I've made air hold tools from an old spark plug, brazing an air coupler to the metal shell after knocking out the porcelain and removing the ground strap.  The issue with a simple air hold tool is that you will find an air leak but not know the percentage of leak.  That's the point to the leakdown tester.

Moses

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Harbor Freight was a bust. I tried O'Reily's, Autozone, and NAPA, same thing. I am really disappointed, yet not surprised at this point. Maybe part of the problem is the Jeep cylinder head? I have never paid attention and noticed any engine I worked on (Ford, Chevy, Dodge), but there is a 0.25 inch gap between the threads to top of head. Maybe my Jeep is the issue and not the tools. Whatever is going on, it is what it is, I will adjust.

The good news. I received an email that my order has shipped! Hurray! Since discretion is the better part of valor, I will yield to caution and be patient for the kit to arrive. It will just be a little longer, if it even works, to see numbers. In the mean time, I will try a little Techron or similar product in the tank, and the old misting or small drizzle of water into TBI for a little steam cleaning in the mean time. Hoping that the next kit will work. Fingers crossed.

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Good pick, Nucking Futs!  I see the adapter.  I'm wondering if it was missing from the OTC tool?  This should work!  Decent price, too.  ATD is well known these days.

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The adapter could have been missing. I hope this one will works.

So I have an 1971 DJ5 that I acquired a while back. It was cheap, has lots of issues. Anyways, I thought that pulling the head from the DJ would be a good practice run to see what it will be like pulling the head of my CJ. The bolts are bolts, you turn turn turn them. But lifting that monster of a head off the deck, dam! That head is a beast!

WD40 seems to loosen carbon reasonably. Add some elbow grease and brillo pads and it works wonders on removing carbon.

So cleaning the carbon won't be too bad. Removing the head will be a chore. Installing the head, that will be a challenge without damaging the head, mating surface, the gasket, my fingers, back, or some other part of my body! A hoist would come in handy for this job. 

 

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#4-50% leakage, #2-40% leakage, all through intake valve. Odd. Run up to #1 visually into cylinder as I rotated by hand and I could see no cylinder movement as I rotated crank. Timing mark is at 4* before TDC. This would make sense as I tried 4* and it backfires through the carb. 

So it appears that my valve train is not in time and advanced about 3-4*. Now, is that from chain slack and it jumped, or because someone has been in there and tried some "special" timing. 

I'm going to see what I can do for the rest of the cylinders.  

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Every cylinder same results, 40-50% leakage through intake. If I run crank till valves are closed, the air pressure runs to the engine to the next cylinder and reads 100% leakage.

I've always thought my cam was not in time for a few years now. That is now confirmed. Why is it is the mystery. 

I suspect someone has been in there and done some engine work. Block and head are not stock looking color, valve cover has been replaced with an aluminum cover (not really a good one but it shows someone was dressing her up), odds and ends. Compression is pretty darn good for a 170xxx 4.2L being over stock specs. My hypothesis (not geometry) is a rebuild. Maybe the head was shaved too bump compression chasing a few HP? New cam profile timing chasing top end HP? I have no idea. 

Or maybe the chain just jumped. 

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2 hours ago, Nucking Futs said:

#4-50% leakage, #2-40% leakage, all through intake valve. Odd. Run up to #1 visually into cylinder as I rotated by hand and I could see no cylinder movement as I rotated crank. Timing mark is at 4* before TDC. This would make sense as I tried 4* and it backfires through the carb. 

So it appears that my valve train is not in time and advanced about 3-4*. Now, is that from chain slack and it jumped, or because someone has been in there and tried some "special" timing. 

I'm going to see what I can do for the rest of the cylinders.  

Correction, the cam timing is retarded (intake close timing is delayed). Valves are still open at TDC. I don't hear slap or rattle form chain. Intuition is telling me this was done on purpose. 

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Umm...So you brought each piston up on its compression stroke, not on the exhaust stroke?  At the top of the exhaust stroke, the intake valve opens.

Simple solution:  Remove the distributor cap and watch the rotor as you rotate the crankshaft.  The rotor should point to the cylinder you are testing at TDC.  If the rotor is facing opposite the cylinder you are checking, you are on TDC of the exhaust stroke and not TDC of the compression stroke.  This would create an intake valve leak.  As you test each cylinder, the cylinder being tested should have the piston at top-dead-center and both valves closed.  

The TDC mark on the crankshaft and timing cover will only index with #1 and #6 cylinders.  The firing order is 1-5-3-6-2-4.  When #1 piston is at top dead center with both valves closed, that is the top of the compression stroke and where you want to test for leakage.  #6 cylinder's piston is also at top dead center but with the intake valve beginning to open.  #6 piston is at the top of its exhaust stroke with the intake valve beginning to open.  To test leakage in #6 cylinder, rotate the crankshaft 360 degrees.  Use the distributor rotor as a guide for which cylinder is up to fire at the top of its compression stroke.

Each of the other cylinders requires watching the piston reach top dead center and confirming that the piston is on its compression stroke.  You can mark the crankshaft pulley each 120 degrees if you like.   That would provide the reference points for TDC on cylinders 5, 3, 2 and 4.  Most techs simply watch the rotor and follow each piston to top-dead-center on its compression stroke.  Shine a light in the spark plug hole if necessary to confirm that the piston is at top dead center.  Make sure both valves are closed by noting the position of the distributor rotor.

If you're curious about timing chain wear, a simple test with the distributor cap removed is to rotate the crankshaft in its normal direction and stop at the TDC mark on the timing cover.  (If you pass the mark, rotate the crankshaft backward 45-degrees and come forward again slowly, stopping at the TDC mark.)  Now, while watching the distributor rotor, slowly rotate the crankshaft backwards until you see the rotor just begin to move.  Note the inch measurement of movement at the surface of the crank pulley.  If the crankshaft pulley's surface/circumference has moved more than 5/8" before the rotor begins to move, there is excessive timing chain slack.

This is a rough check and subject to the amount of wear on the camshaft drive and distributor gear.  If the distributor driven gear is in good shape, I like to see 1/2" to 5/8" maximum crank pulley surface/circumference movement with a pulley this diameter.  If you have too much movement, that's play.  Too much play is time to change the timing sprockets and chain.

Moses

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Moses, I'm pretty sure I did it correctly. If the timing mark is on TDC, #1 is up to top, the rotor is pointing to #1 plug wire, I should be on intake stoke, yes?. #1-6 are paired but #6 at exhaust and #1 at intake I understand. #2-5, #3-4 are paired if I recall correctly in the same manor. I did follow the firing order, noted where the rotor is in relation to the cap for firing and position of cylinder.

I can redo the test to verify, as it is pretty easy to do and will not hurt doing it again, but will have to be after work tomorrow. I will also try rotating the crankshaft back after I stroke is on #1 TDC to check total distance to timing mark travels before rotor begins to move.

I hope I did the test wrong. 

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Nucking Futs...I'm optimistic that the engine does not have severe intake leakage.  Your cranking compression is too good for these leak percentages and air gushing out the intake.  Of course, when you test again, you will listen for air at the intake.  Just be certain the valves are both closed, and the piston is at the top of the cylinder.  And yes, pairs are 1-6, 2-5 and 3-4.  Use the rotor to distinguish which stroke.

Time for sleep and a workday ahead...Pick it up tomorrow.  If you still suspect valve timing issues, a quick test is manifold vacuum at an idle.  From there, with the valve cover removed, you can test the actual valve opening and closely events/degrees with a degree wheel or crank damper timing tape that covers the full circumference of the crankshaft damper.  A dial indicator at the rocker arms will help measure the valve opening and closing events.  You only need to check valve timing at #1 cylinder.

Moses

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Quick lunch break test.

Timing mark set at TDC. #1 cylinder visible through spark plug hole. Rotor pointing towards #1 position on cap. #1 has 45% leakdown with air moving through intake (sound adjustable by opening butterfly in TBI). Without rotating engine, I removed the hose and tried #6 to see if I was on wrong cylinder. #6 had leaked also. I tried various positions on the timing mark to see if I could find where valve was actually closing. I could no find it as psi pushed piston either backwards or forwards depending on position in stroke. I tried putting a wrench on the crank nut to lock crackshaft from moving, but I had moderate success doing that and still had leakage. I need an extra set of hands! The only way to positively know when valves are closed will be to remove the valve cover off. I may do that later.

I decided I would try something a little easier and see how much stretch is in the timing chain. I rotated the engine all the way around to take up slack and I set timing make to TDC on timing cover. I then rotated the crank back until the rotor moved. It took between 3/4rd" to 7/8th" of an inch of movement on the dampener before the rotor moved. That is past the 5/8th" you mentioned. Considering the slack in the chain and my valve closings do not seem to match TDC I am still thinking: (a)-the chain is unable to keep time because of the slack, or, (b) chain jumped and is out of time.

I can verify #1 intake valve closing and opening by pulling off the valve cover, rotor through the cycle, and note the position of the crank timing mark in relation to the #1 intake valves opening/closing.

But is that really necessary and worth my time with that much slack in the timing chain? I think doing anything else it is an exercise of futility. As you stated, compression numbers are good. Even if the numbers are off 20%, they are still good. I know I need a new chain. In a real simplified way, I see the compression test indicates that my engine is holding air just fine. The leakdown test says I have a timing issue in relation to the movement of air at the correct time.

I don't know 100% though. I'm not a mechanic, I just play one on the internet :D.

 

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Nucking Futs...If you feel ambitious, removing the valve cover would answer a few questions about valve opening events and valve timing.  Note when the rocker arms open and close at #1 cylinder.  Compare this with the rotor position and timing marks. 

Is there a possibility that the timing cover and damper are a mismatch?  One problem is a timing cover coming from an earlier IH Scout 258.  The damper mark will not index with the piston at true top-dead-center for #1 cylinder.  I covered this topic here:

Another issue, far more common, is a damper ring that has crept on the pulley hub.  Here, the damper mark will not align properly with the TDC mark on the timing cover.  The easiest way to verify this is to bring #1 piston to the very top of the cylinder (do not pass that point).  With the piston in this position, look at the damper mark and timing cover TDC mark.  If they do not align, the damper is creeping on its hub, or the timing cover is incorrect for the damper style.

There is an inexpensive tool that I have recommended for finding true top-dead-center for #1 piston.  Forgetting about the timing marks for the moment, concentrate on #1 piston's true position in the cylinder.  This tool is flexible and will not jam against the piston crown.  Avoid gauges that can scuff the piston crown:

https://www.amazon.com/Innovative-Products-America-7880-Indicator/dp/B002XMOMA2/ref=sr_1_1

If it turns out that your timing marks are off, you answer several questions, including:  1) why setting the spark timing with a light leads to detonation/ping, 2) why air is pushing out the intake when you use the timing marks to locate TDC, and 3)  why there is a discrepancy between the timing marks and #1 piston's actual alignment with the top of the cylinder.  Concentrate on #1 cylinder as your example.  The other cylinders will follow as we have discussed.

The timing chain does have wear, but if a damper alignment problem exists, concentrate on getting that straightened out.  You may need a new damper.  You may just want to make a new, accurate TDC mark on the damper for now.  After you run a valid leakdown test, you can reset the ignition timing based on an accurate TDC mark.  This will help engine performance and meet smog requirements.

Moses

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Moses, at this point I would say anything is possible! What I do know. I have an C-block with serpentine belt drive. The timing cover has the magnetic probe socket. Is the V-belt cover compatible with the serpentine belt?

Pulling the valve cover may be best option at this point since the possibility of mismatch parts is plausible. While I don't think this has happened, I need to verify this to rule out uncertainty.

I employed the visual method of looking through the spark plug hole to find TDC. I know that there is a moment when the up-travel stops and the crank is still spinning . How many degrees am I off from true TDC I don't know, but I am close enough that the valve is suppose to be closed at this moment. Looking at the timing mark it is around 4* before and valve is open. If I rotate the crank to the TDC, valve still open. Past TDC and the air pressure will push the piston down. If I try 8* before, the air pressure will spin the crank backwards. Because I am looking at TDC for timing and not the timing mark, this is why I am thinking there is cam timing error. The stretch in the chain has me thinking the chain jump may be a real possibility. So I will pull the cover off and verify when the valves are closed according to the rocker arms. I can then see where the timing mark is. If you know approximately how far off the IH cover is from the Jeep cover that would be helpful. For creep, I'm probably on my own. Inspection of damper when timing gear and chain is replaced may tell. And the Jeep passes smog with no issues btw.

The tool looks like a winner and will add it to my collection. In the meantime I have some work to do.

 

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Nucking Futs...When you get the valve cover off with #1 piston at a visual (close enough for this check) top-dead-center in #1 cylinder, both valves should be closed.  If the intake rocker is definitely opening, slowly rotate the crankshaft another 360-degrees.  As you rotate the crankshaft, note the valve opening and closing events at the #1 cylinder's rocker arms.  If you see the intake valve immediately open further then close completely as the piston rises to top-dead-center at #1 cylinder, and if both valves remain closed as the piston comes up to the top of the cylinder, you are now at the top of the compression strokeThis is where you run the leakdown test.

Let's leave the  rotor out of the picture for the moment.  We're concerned about valve opening and closing events in relationship to the #1 piston's position in the cylinder.  If the valves/rockers are out of sync with the #1 piston/crankshaft movement, you have a valve timing issue:  1) either the chain has jumped or 2) somebody installed sprockets and a chain without aligning/indexing the sprockets properly. 

The timing chain does have wear.  Whether enough to "jump" teeth and change valve timing is the question.  The timing chain is on the margin for loose enough to jump time.

Moses 

 

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Hi Moses. I think the wind was sucked out of my sail after my last go around with the Jeep. Not as good of news as I was hoping, but could be worse. The engine still runs at least. Here is the report.

With the valve cover off, I visually looked to see TDC for #1 and went around several times and tested at both positions just to make sure. I did observe the rotor for a last double check.

I watched for the rockers to stop moving, and wiggled them to see if there was any tension on them. No tension present with just a slight twisting from my hand on the rockers at TDC. Looking at the timing mark at TDC, it appears that the valves are closed when they are suppose to be. When I did the leakdown test, the engine did not spin, another indication I was at TDC (if I am not at TDC the engine will spin forwards or backwards as I apply 100psi). Sigh!  I still have ~45% leakdown. This is disappointing. I was hoping for a simple timing set replacement. Kind of weird that compression numbers where so high with that much leakage. I would say one of the gauges is wrong. Since I can hear air escaping into the intake manifold, I would bet the HF compression gauge is likely off. 

I need a new timing sprocket/chain this I know. I also have an internal vacuum leak via the intake valves, this I know. The leak could explain why it wants to idle a little higher. The spark knock I would say is from the excess carbon.

I thinking that my cylinder head needs servicing, more than I can do. Either carbon is hold valves open or the issues with stem and/or seats, and likely a combination of all of these. If my cylinder head does need work, doing just a top-end rebuild doesn't make sense with 170,xxx miles. I was always taught this with speed accelerate wear on the piston rings.

I have some thinking to do. In the meantime, I would like to hear your analysis Moses.

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Nucking Futs...You took the step that makes a difference:  valve cover renewal to confirm that the valves are closed.  You have a true leakdown reading now.

The HF gauge may or may not be accurate (another story), but the air in the intake stream is definitely a leak.  Did you hear air at the valve cover or dipstick tube?  That would be ring blow-by.

45% leak with a higher cranking compression seems counter-intuitive, but it is not.  This is most often cylinder taper, which is toward the top of the cylinder.  Aside from keeping the piston from pushing down under air pressure, we run a leakdown test at TDC because this is the highest wear point in the cylinder for taper—or the maximum taper point.  The leakdown test is deadly accurate for predicting piston ring wear and taper.  The piston rings have the least tension and the widest ring gap in this position.

So, why is cranking compression high or "normal"?  Because cranking compression is a moving piston that captures air and forces it into a gauge with a one-way Schrader valve.  The spinning crankshaft drops the piston low enough to get a good gulp of air, and the ring movement past the taper area is momentary enough to offset a large amount of leakage past the rings.  The compression gauge gives a high, stacked reading.  This is why a compression test is run with no more than 5 or 6 spins of the crankshaft.  Many believe they should keep cranking to the highest reading.  When we do that, we're stacking air into the one-way gauge and getting a false reading.

The leakdown tester is likely right, and this is relative, anyway.  20% would be acceptable.  Even your 45% leakage is offset by the relatively "normal" (possibly high due to carbon buildup) cranking compression.  If the engine is not burning oil, you could "get by" with more miles of driving this 4.2L engine.  Cylinder balance between cylinders will be questionable, which you notice when under load or cresting the Sierra Range (where the rarefied atmosphere lowers the compression).  We loose 3% of engine power per thousand feet of elevation.  Unless the engine is turbo or supercharged, horsepower drops approximately 24% at 8,000 feet elevation. 

You are absolutely correct about a valve grind boosting compression and shortening the life of the worn piston rings.  This is due to cylinder taper and ring wear.  If you hear ring blow-by in the crankcase, it's safe to assume from your leakdown test that this block will require reboring during a rebuild.  The long stroke on the 4.2L nearly guarantees this, as the piston travel in 170,000 miles is much greater than it would be with a shorter stroke engine.  If this engine has never been rebuilt, taper is highly likely.

I do want to know whether you heard air from the crankcase, aside from the intake stream/valve leak.  If you ran the leakdown test with the valve cover removed, ring blow-by air would be coming through the pushrod openings.  If the valve cover is in place, ring blow-by or crankcase air can be heard at the dipstick tube or with the oil fill cap removed from the valve cover.

Your leakdown tester is pressing a good amount of steady air into the cylinder.  It is measuring the amount of air that escapes the cylinder.  That air escapes past the rings, valves, a blown head gasket or casting crack.  A blown head gasket or casting crack can be ruled out unless there are bubbles in the radiator.  Valves you know are leaking from the air in the intake stream.  (Listen at the tailpipe for exhaust valve seepage.)  Ring blow-by should be heard from the dipstick tube, oil fill cap or with the valve cover removed.  This is air moving past the rings into the crankcase, which is audible at the dipstick tube or oil fill cap.

Confirm the air seepage into the crankcase for an accurate ring wear and cylinder taper diagnosis.  I like to run the piston down the cylinder a bit, either before or past TDC (enough to get the rings below the maximum taper point with the valves still closed).  Then I keep testing.  If the piston will stay there (like you share, it wants to push the piston down under air pressure), I take a leakage reading in that position.  If the leakage is clearly less than the 45%, cylinder taper is the reason.  Lower in the cylinder, the taper decreases and rings can seal better.  Be aware that leakage does increase some as air blows oil off the cylinder wall.

On that note, a test that sometimes works with the piston at TDC is to squirt a teaspoon or so of clean engine oil into the spark plug hole and run the leakdown test.  If this momentary increases the cylinder seal, the cylinder has worn rings and cylinder taper.  (The oil temporarily seals around the piston edge and rings.)  With air not leaking past the piston rings, the leakdown percentage will drop.  To prevent spark plug fouling, let tester air run into the cylinder for a bit to clear the oil from the upper cylinder before installing the spark plug.

Once you have pinpointed the air noise locations, your leakdown tester has paid for itself.  You know the engine condition before tear down. 

Moses

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8 hours ago, Moses Ludel said:

Nucking Futs...You took the step that makes a difference:  valve cover renewal to confirm that the valves are closed.  You have a true leakdown reading now.

The HF gauge may or may not be accurate (another story), but the air in the intake stream is definitely a leak.  Did you hear air at the valve cover or dipstick tube?  That would be ring blow-by.

45% leak with a higher cranking compression seems counter-intuitive, but it is not.  This is most often cylinder taper, which is toward the top of the cylinder.  Aside from keeping the piston from pushing down under air pressure, we run a leakdown test at TDC because this is the highest wear point in the cylinder for taper—or the maximum taper point.  The leakdown test is deadly accurate for predicting piston ring wear and taper.  The piston rings have the least tension and the widest ring gap in this position.

So, why is cranking compression high or "normal"?  Because cranking compression is a moving piston that captures air and forces it into a gauge with a one-way Schrader valve.  The spinning crankshaft drops the piston low enough to get a good gulp of air, and the ring movement past the taper area is momentary enough to offset a large amount of leakage past the rings.  The compression gauge gives a high, stacked reading.  This is why a compression test is run with no more than 5 or 6 spins of the crankshaft.  Many believe they should keep cranking to the highest reading.  When we do that, we're stacking air into the one-way gauge and getting a false reading.

The leakdown tester is likely right, and this is relative, anyway.  20% would be acceptable.  Even your 45% leakage is offset by the relatively "normal" (possibly high due to carbon buildup) cranking compression.  If the engine is not burning oil, you could "get by" with more miles of driving this 4.2L engine.  Cylinder balance between cylinders will be questionable, which you notice when under load or cresting the Sierra Range (where the rarefied atmosphere lowers the compression).  We loose 3% of engine power per thousand feet of elevation.  Unless the engine is turbo or supercharged, horsepower drops approximately 24% at 8,000 feet elevation. 

You are absolutely correct about a valve grind boosting compression and shortening the life of the worn piston rings.  This is due to cylinder taper and ring wear.  If you hear ring blow-by in the crankcase, it's safe to assume from your leakdown test that this block will require reboring during a rebuild.  The long stroke on the 4.2L nearly guarantees this, as the piston travel in 170,000 miles is much greater than it would be with a shorter stroke engine.  If this engine has never been rebuilt, taper is highly likely. One of the previous owners (original?) towed it as it had a wire loom into the front of the Jeep for stop/turn lights. The owner before me I think just used her a little too hard.  In 37 years, anything is possible with the Jeep. All that to say I suspect block work will be needed and expected. 

I do want to know whether you heard air from the crankcase, aside from the intake stream/valve leak.  If you ran the leakdown test with the valve cover removed, ring blow-by air would be coming through the pushrod openings.  If the valve cover is in place, ring blow-by or crankcase air can be heard at the dipstick tube or with the oil fill cap removed from the valve cover. Negative, no air felt or heard from dipstick or pushrod galley. No noise felt or heard through tail pipe. It seems to be isolated to the intake. The noise level is rather loud. I could smell the gasoline fumes and sound would change as I opened the butterflies on the TBI.

Your leakdown tester is pressing a good amount of steady air into the cylinder.  It is measuring the amount of air that escapes the cylinder.  That air escapes past the rings, valves, a blown head gasket or casting crack.  A blown head gasket or casting crack can be ruled out unless there are bubbles in the radiator.  Valves you know are leaking from the air in the intake stream.  (Listen at the tailpipe for exhaust valve seepage.)  Ring blow-by should be heard from the dipstick tube, oil fill cap or with the valve cover removed.  This is air moving past the rings into the crankcase, which is audible at the dipstick tube or oil fill capNo bubbles in radiator (oil in water or water in oil), No audible noise from dipstick or tail pipe. No air felt from the dipstick either. I do get blow by from the dipstick at the base where it attaches when she starts gettning around 2200+ RPM. It will blow out the dipstick a little too. I had the PCV system hooked up wrong. That has been corrected but I still get a little but not bad. 

Confirm the air seepage into the crankcase for an accurate ring wear and cylinder taper diagnosis.  I like to run the piston down the cylinder a bit, either before or past TDC (enough to get the rings below the maximum taper point with the valves still closed).  Then I keep testing.  If the piston will stay there (like you share, it wants to push the piston down under air pressure), I take a leakage reading in that position.  If the leakage is clearly less than the 45%, cylinder taper is the reason.  Lower in the cylinder, the taper decreases and rings can seal better.  Be aware that leakage does increase some as air blows oil off the cylinder wall. I could not confirm air into the crankcase, I suspect operator error. I ran the cylinder to 8* BTDC and leakage was almost 65%. I forced the cylinder as close to TDC I could against the pressure. The leakage would decrease to 40-45% as I moved the piston towards TDC. I tried testing between 1/2 to 3/4 below TDC and leakage was 80%. I have no idea what to make of that.

On that note, a test that sometimes works with the piston at TDC is to squirt a teaspoon or so of clean engine oil into the spark plug hole and run the leakdown test.  If this momentary increases the cylinder seal, the cylinder has worn rings and cylinder taper.  (The oil temporarily seals around the piston edge and rings.)  With air not leaking past the piston rings, the leakdown percentage will drop.  To prevent spark plug fouling, let tester air run into the cylinder for a bit to clear the oil from the upper cylinder before installing the spark plug.

Once you have pinpointed the air noise locations, your leakdown tester has paid for itself.  You know the engine condition before tear down. All I can hear is from the intake manifold. She runs still. She just is lacking. Deer season is fast approaching so I need her to be ready for the mountains.  I am thinking that she is do for a full rebuild. 

With that in mind, my initial plan is to find a quality shop (do you know of any around the Sacramento area?) to rebuild her. I would love to do it myself, I just don't have the room to do at my location currently. I want to keep the 4.2L block. If I could make the 4.0L head work that would be ideal. 

Moses

 

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Nucking Futs...You did thorough and conclusive work here.  The 8-degrees BTDC could be more space for air leakage from the taper area.  At true TDC the top ring is butted against the cylinder ridge, which may decrease the leak to 45%.  This also shows that there is ring blow-by.  The 1/2 to 3/4 BTDC could be valve overlap, you could determine that again with the valve cover removed, but why bother.  You have enough information to reach your conclusion about a complete rebuild.

The silver lining is your investment in the TBI system.  Aside from the long stroke and piston travel, the original 4.2L with a carburetor was not able to control air/fuel ratios like the Howell EFI.  Rich fuel mixtures from a carburetor will fuel wash the cylinder walls (reducing oil protection) and hasten ring wear and taper.  I've never done the Nutter Bypass but would like to see air/fuel ratio changes from this modification.  I am familiar with the 4.2L BBD Carter carburetor and suspect that the bypass may create richer air/fuel ratios.  (I would like to see an oxygen sensor monitor reading before and after the modification.)  The OE Sole-Vac tries to adjust for more precise air/fuel ratios.  Without Sole-Vac, the system may run richer, increasing the risk of fuel washing the cylinders.  In any case, you're past the BBD.  The Howell EFI will keep a lid on fuel enrichment.  Cylinder wall lubrication is much better with EFI.

As for the 4.0L cylinder head, this would make sense for improved combustion and reducing the detonation tendency.  As I mentioned earlier, you do need to be sure that your current (BBD carburetor application) intake manifold will fit the 4.0L head.  You noted that the exhaust manifold change is needed.  Aside from exhaust system routing work (a muffler shop sublet), there's not much more involved.  Presumably, the Howell O2 sensor will fit that later exhaust manifold.  If necessary, consult with Howell to confirm this.  The 4.0L cylinder head has a few cooling ports that must be blocked off for use with a 4.2L cylinder block.  The machine shop should have ideas on best practice here.  If not, we can discuss the modification options.

You're the judge of the right time for rebuilding the engine.  Can you "get by" for a while, including deer season?  Reliability is vital for backcountry travel, though the engine is not in peril or burning a lot of oil.  Power is obviously down, and at altitude that will be more noticeable, especially on the highway.  (In low range off-pavement, power is a non-issue.)  Monitor the relative condition of the engine. 

As for rebuild shops in the Sacramento Area, there should be many.  I'm on the Reno side of the range and not familiar with specific Sacramento shops.  Word of mouth and reviews help.  A personal visit to shops, knowing their equipment and being clear about the shop's familiarity with the 258/4.2L would be wise.  

I recommend balancing the lower end reciprocating parts.  If your OE flywheel can handle resurfacing, include that plus balancing.  Quality shops quote balancing in any estimate. 

Expect 0.030" reboring from stock, the days of 0.010" and 0.020" oversize bore and pistons are gone.  Shops buy parts through sources that service the "reman" industry, and reman shops bore every engine to 0.030", beyond that if necessary.  For cooling and wall stability, go with the 0.030", no more if avoidable.  0.010" undersize on the crankshaft is ideal, 0.020" acceptable (0.030" for a damaged crank).

The shop should include a new camshaft, lifters and cam bearings.  A Cloyes or quality equivalent double-roller timing chain and sprockets are advisable on these engines.  New pushrods must be sized for correct lifter preload.   

Good cylinder head reworking (3-angle seats, etc.) with installation of hard steel exhaust valve seats and exhaust valves is highly recommended for running unleaded fuel.  

Let us know what you find and how this all turns out...

Moses 

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Thanks Moses. 

My next journey is to find a quality builder. I do want to have the engine balanced. From my understanding, it will smooth out the engine more which will also aid in prolonging the overall life of the engine, a worthy investment of cost. 

Searching the internet I have found several business that offer new casting 4.0L heads, and others that prep the head for the 4.2L. Hesco still makes their 4.0L head, and there is always Edelbrock's head. The later two are expensive, and I don't want to blow half the budget on just the heads. I will be visiting the local auto recycler yards in search of intake and exhaust manifolds. I will need to contact Howell about the O2 sensor locations between the 4.2L and the 4.0L stock locations. I don't think it will make a significant difference, but I am sure they will know. 

I do have a question about cams. I know you previously were a proponent for the Comp 264H grind (I believe that was the one) from one of you videos you made. Considering that I have the Howell TBI and the associated MAP sensor, what differences in cam profile are needed for the TBI system? I drive and live in the low to mid power band, I generally keep the engine under 2500 rpm. That is the sweet spot of the 4.2L.

More to come and I will post progress as it happens. One good outcome from all this is I will have a fresh new rebuilt engine. 

 

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Nucking Futs...My recommendation has always been the CompCams 252H grind for these engines.  It provides strong power to 4,500 rpm and runs well to 5,000-plus rpm, either spinning fast for a 258!  My choice is based upon the low-end torque this camshaft provides due to better/more valve lift with milder duration. 

This is a true torque grind, often referenced for towing or RV use.  You will have strong bottom end, excellent idle and tip-in manifold vacuum.  Good for fuel efficiency, too.  I judge an off-pavement camshaft by its manifold vacuum at lower speeds.  This camshaft delivers higher manifold vacuum.  I have run the 252H grind in otherwise stock EFI engines like the 4.0L (up through 1999) and Ford MPI/EFI 300 cubic inch sixes.  For late 4.0L engines (distributorless Coil-On-Plug) with camshaft timing overrides in the PCM, CompCam does not recommend this camshaft.  (They have a preferred grind for these late engines.)  Any other inline six, carbureted or EFI, will benefit.  I ran this grind in carbureted 383 Chevrolet small-block stroker V-8s as well.

I avoid the 264H, though it's great for mid-range and top end power if that's what a user wants (sand dunes, mud bogging, etc.).  I have used 258s in their intended environment:  crawling and lower speeds off-pavement.  252H torque transfers to horsepower in the mid-range and at highway cruise speeds in the 2000-3000 rpm range.   This is a strong puller to 4,500 rpm, running out near 5,500 rpm.

Moses

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1 hour ago, Moses Ludel said:

Nucking Futs...My recommendation has always been the CompCams 252H grind for these engines.  It provides strong power to 4,500 rpm and runs well to 5,000-plus rpm, either spinning fast for a 258!  My choice is based upon the low-end torque this camshaft provides due to better/more valve lift with milder duration. 

This is a true torque grind, often referenced for towing or RV use.  You will have strong bottom end, excellent idle and tip-in manifold vacuum.  Good for fuel efficiency, too.  I judge an off-pavement camshaft by its manifold vacuum at lower speeds.  This camshaft delivers higher manifold vacuum.  I have run the 252H grind in otherwise stock EFI engines like the 4.0L (up through 1999) and Ford MPI/EFI 300 cubic inch sixes.  For late 4.0L engines (distributorless Coil-On-Plug) with camshaft timing overrides in the PCM, CompCam does not recommend this camshaft.  (They have a preferred grind for these late engines.)  Any other inline six, carbureted or EFI, will benefit.  I ran this grind in carbureted 383 Chevrolet small-block stroker V-8s as well.

I avoid the 264H, though it's great for mid-range and top end power if that's what a user wants (sand dunes, mud bogging, etc.).  I have used 258s in their intended environment:  crawling and lower speeds off-pavement.  252H torque transfers to horsepower in the mid-range and at highway cruise speeds in the 2000-3000 rpm range.   This is a strong puller to 4,500 rpm, running out near 5,500 rpm.

Moses

Compcams 252H, got it! My mistake on the 264H. Thank you sir. I do appreciate the all the advice. 

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