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Hello. I'm new to the forum. I have an 82 CJ7 with a fresh rebuild 258 and the Hesco MPI installed by myself. At low power the engine runs fine. But under load, say going uphill or when giving a sudden throttle input in a higher gear, the engine begins to misfire or cut out as though one or more cylinders are not firing. If I ease up on the throttle it recovers. If not it shudders pretty bad until I do. If I go easy on the throttle the problem does not occur. Only under load. At cruise speed on the freeway it mostly runs good, but occasionally I do feel a slight power loss as though I am dragging a cylinder. The plugs are clean so I don't suspect an ignition issue. It acts like its running out of gas.

Thoughts or suggestions much appreciated.

 

Lou

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Hi, Lou...It does sound like you're "running out of gas".  This is likely a fuel supply issue.  Since you refer to the system as "HESCO", I am guessing you have the late MPI with a single rail EFI?  This system would have no return line from the fuel rail to the tank.  The earlier MPI/EFI has a two-rail EFI, which means there is a return line to the tank.

Fuel pressure is not the full picture; however, I recommend that you confirm the fuel pressure at the rail.  This can be done at the Schrader valve test port with a test gauge.  First confirm the correct fuel pressure with the engine running.  It should be steady and the right range.  If you confirm which fuel system you have, single rail or two-rail, I can furnish the fuel pressure range requirements.  In basic terms, the single rail system uses the same operating pressures as a Jeep TJ Wrangler 4.0L (1997-up prototype).

I am suspicious of your fuel supply from the tank to the rail.  There could be a restriction in the flow.  Some possibilities would be 1) a clogged sock pickup in the tank, 2) a kink in a fuel supply line, 3) the kit's pressure regulator is defective (which will show up as low fuel pressure at the rail), 4) the inline electric fuel pump (if part of the kit) is mounted at the front of the vehicle instead of near the tank as recommended, 5) the fuel pump is defective or 6) the supply fuel line diameter is too small.  The OEM mechanical fuel pump should be removed; a block-off plate is installed at the original fuel pump slot in the engine block.  

I would confirm the fuel volume flow at the rail.  This can be done with a safe metal can and a hose from the Schrader valve (test port) to the can.  With the hose connected and Key ON, there should be a strong, steady flow of fuel.  A low volume of fuel is the concern here.  Fuel pressure alone is not enough.

These EFI systems will not vapor lock.  The fuel is constantly returning to the tank from either the return rail or from the EFI kit's regulator (which should be mounted near the tank).  If you have the single rail system with modified the kit's TJ style pressure regulator, there is a very remote possibility of "vapor lock" if the fuel line between the pressure regulator and EFI rail runs too close to a high heat source. 

As a rule, recirculating fuel does not vapor lock.  As a point of interest, the 4.2L stock fuel system had a three-pipe fuel filter with a return line to the tank to keep fuel moving and resist vapor lock.  Many late carbureted engines with mechanical fuel pumps have three pipes on the fuel pump with one line returning the excess fuel to the tank.  This helps prevent vapor lock.  Classic vapor lock occurs when heat vaporizes fuel within the fuel line and creates gaps.  This usually happens when the engine is hot and fuel is static or has very low flow rate.

Moses 

 

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  • Moses Ludel changed the title to Jeep 4.2L HESCO MPI/EFI Conversion Misfire

Moses,

Thanks for the reply. I have the single rail system. The pump and and regulator (both supplied with the kit) are mounted on the rear cross member as per the kit instructions and the stock mechanical fuel pump has been removed and the block off plate installed on the engine block. 

The fuel supply line runs from the pump and regulator up the passenger side (I used the existing stock line) and connects to EFI rated rubber fuel line which crosses under the radiator along the frame rail to the driver's side. So heat should not be an issue unless the injectors or fuel rail are getting excessive heat rising up from the exhaust manifold.

I have a new gas tank installed, so I am doubtful of the clogged pick up sock. But I picked up a new fuel filter (located between the tank and pump) and will replace it precautionary. I'll cut it open and check for any debris.

I will check the fuel flow and pressure later today or tomorrow and get back to you.

Lou

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Hi, Lou...See my comments below in red:

19 hours ago, Lou said:

Moses,

Thanks for the reply. I have the single rail system. The pump and and regulator (both supplied with the kit) are mounted on the rear cross member as per the kit instructions and the stock mechanical fuel pump has been removed and the block off plate installed on the engine block.

That helps clarify... 

The fuel supply line runs from the pump and regulator up the passenger side (I used the existing stock line) and connects to EFI rated rubber fuel line which crosses under the radiator along the frame rail to the driver's side. So heat should not be an issue unless the injectors or fuel rail are getting excessive heat rising up from the exhaust manifold.

You can use an inexpensive thermal infrared surface heat tester (Harbor Freight will due here) to check engine and radiator heat, testing the temperature at various points along the fuel line.  Doesn't sound like you will turn up a problem here.  The radiator should not be an issue if the fuel line is at least a couple inches from the radiator core.  The radiator core temperature can exceed boiling temperature.  The temp tester is a valuable tool for spot checking heat, you'll find many uses for this device.

I have a new gas tank installed, so I am doubtful of the clogged pick up sock. But I picked up a new fuel filter (located between the tank and pump) and will replace it precautionary. I'll cut it open and check for any debris.

Very good idea!  A paper matrix fuel filter can clog from one bad tank of fuel with high water content 

I will check the fuel flow and pressure later today or tomorrow and get back to you.

Fuel volume and pressure each play a role here.  Looking forward to your findings.  You might test fuel flow at the engine side of the old fuel filter before changing it, then do the same check at the new fuel filter.  You want to check the volume and pressure.  For a single rail system (FSM data for 1998 TJ Wrangler 4.0L engine) that uses a pressure regulator similar to your modified device in the EFI conversion kit:

1) Fuel volume should be a minimum of 1/4 liter in 7 seconds of pump operation;  pump should not be activated for more than 7 seconds of flow.

2) Pressure at the rail test port should be 49.2 PSI (+/- 5 PSI) with the engine warm.  With a stock 4.0L fuel supply system in a TJ Wrangler chassis, after shutting off the engine, the rail test port pressure should hold at least 30 PSI for five minutes.  (This value is for a stock fuel system that has an in-tank module and fuel check valve.)  See what your readings turn up.  

Lou

 

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Results from today's troubleshooting:

  • I replaced the fuel filter and cut it open. The filter element is clean.
  • The fuel flow produced a volume of 170ml in 7 seconds. I repeated this three times with identical results. This is low based on your information that it should put out 1/4 liter (250ml) in 7 seconds. This was with a new filter installed. I did not think to check the fuel flow with the old filter. Note: I checked the flow from the shrader valve port on the fuel rail. Is this correct?
  • The fuel pressure reads 46psi at all operating RPM's and holds at least 30psi for more than 5 minutes.

Do you suspect a bad pump? Or some other restriction?

Lou

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The Schrader valve stem restricts the flow.  Mopar does this test by disconnecting the flex fuel supply line that feeds the rail.  This requires a spring retractor tool and a special Tee adapter. An inexpensive spring retractor hose disconnect tool set is available; however, you likely don't have the adapter.  A simple alternative:  Make a Tee that will fit the fuel supply hose at the engine side of the fuel filter.  This would be an ample hose size for an accurate flow test. 

You could get creative and make a test "tool" with a 3-way Tee that you splice into the fuel line past the fuel filter (anywhere past the fuel pressure regulator, fuel pump and fuel filter).  This could be nearer the engine in a convenient position and away from heat.  The Tee would have three ports:  two ports (straight through) would be the normal fuel flow, and the Tee port could be plugged when not in use.  (There are NPT plugs or flare seat plugs available, whichever fitting type you want to use.)  When you need to test fuel pressure and volume flow, you would remove the plug at the Tee and install either a hose to a remote metal container (flow test) or a pressure gauge (for pressure testing).

Since you have a single rail system, the kit's pressure regulator returns excess flow/pressure into the fuel tank return tube.  Anywhere between the pressure regulator and engine, the pressure should be in the normal range.  Your 46 PSI is well within range, approximately 3.2 PSI below the "norm" but still within the +/- 5 PSI range.  (Ideally,  I like to see +/- 2 PSI, but 3.2 PSI should flow plenty of fuel unless the engine is a stroker 4.6L build.)  If there is a volume/flow issue, this would also impact (drop) the fuel pressure.  The check valve is working if the pressure holds for more than five minutes after you shut off the engine and pump. 

I didn't ask before but guess that you are running a Walbro style inline (external) fuel pump?  The 1987-90 YJ Wrangler 4.2L conversions often use the 1991-95 style OEM fuel tank with an in-tank fuel pump module and gauge sender.  I am assuming you're running the stock tank and pickup tube with the supplied external pump.  What is the lineup of parts?  Is your pressure regulator before or after the fuel pump?  1997-up 4.0L OEM parts orientation would be the tank pickup and fuel pump, then the pressure regulator/filter (mounted atop the pump module).  By design, an inline fuel pump should be pushing fuel from the tank.  They are not designed to draw fuel through the filter.

My first fuel volume suspicion is a pump issue or restriction;  however, the orientation of parts can make a difference before condemning the pump.  If you want to check the fuel pump directly, tap your Tee at the output side of the fuel pump.  The fuel line diameter can interfere with volume flow, though not the pressure readings.  This is usually an issue with a larger displacement engine installation or build that requires more fuel volume. 

On my Mopar EFI conversions, I run 3/8-inch steel fuel/brake rated tubing from the tank to the engine at all chassis areas that do not require flexing.  For flex points between the chassis and body or engine, I run high pressure EFI hose with bubble flares at the tubing connections and use Euro-style EFI hose clamps.  Here are some additional details and installation tips.  Be aware that some photos are for a two-rail EFI conversion kit, others are from a single rail EFI conversion:

https://www.4wdmechanix.com/Jeep-Fuel-Pressure-Requirements?r=1

Moses

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Yes, I should have thought about the shrader valve. I was easily able to disconnect the fuel supply line from the rail.  In addition, I was using an older battery I had in the garage with jumper wires connected to the pump. I realized that this battery was low on juice and not providing sufficient power to the pump. Once I changed to using the good battery in the Jeep and using the main fuel supply line I performed the test three times acquiring 300ml in 7 seconds.

I should note that the engine is NOT a stroker. Its a stock rebuild; nothing fancy. However it is bored 0.040 over. I don't think this would result in a displacement or power increase that would require more pump flow/pressure?

Yes, its the inline (external) pump. Orientation from the tank is filter, pump, regulator.

With the flow and pressure in spec, where do I go from here? It is, of course, difficult to simulate in the garage a problem that occurs at speed under load.

Lou

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Lou...Is this the pump and filter sequence depicted in your HESCO installation guidelines?  I believe you have it right according to the kit layout.  Fuel flow volume and pressure are within spec.

A 0.040" overbore should have no impact on engine fuel demands. Your kit's injectors will easily flow for that displacement. Your fuel pressure is adequate for running your engine to 4500-plus rpm, plenty high for this engine!

I would move to electrical demands and spark timing.  A friend and forum member with the earlier Mopar EFI Conversion had chronic issues with engine misfire and lack of performance.  Symptoms were similar to what you describe...After many rounds of troubleshooting and fruitless approaches, he discovered a fundamental issue:  the four wire main electrical hook-up connections were weak.  The ignition lead, in particular, was a crimp bullet connector with poor continuity.  If you haven't done so already, revisit these connections and solder splice the wires together correctly.  Use a couple layers of heat shrink tubing for insulation.  

Electronic engine management requires very accurate electrical connections.  Interference or resistance will raise havoc.  Since the system is D.C., your ground connections are equally important.  We'll rule out the ignition switch at this point, but that can also be the weak link.

Another concern with these kits is the timing or crankshaft position sensor (CPS or CKS).  This device, from the kits I've installed, attaches to oil pan bolt holes.  Alignment is short of perfect.  I would verify spark timing with a quality timing light.  Check the base timing at idle and also the timing as you open the throttle slowly with the engine unloaded.  Make sure this is on spec.  If necessary, there is a procedure for confirming base timing a step further without sensor input.

Lastly, you could have an issue with pushrod lengths unless you fitted the pushrods for the new cylinder head and block deck heights.  Lifter clearance can be right on the margins and too tight as the engine revs up.  This will often show up with a simple manifold vacuum gauge check, the needle is jumpy and indicates that a valve(s) are not seating properly...Review this forum exchange, especially from my December 25, 2018 reply/post onward:

Moses

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Moses, thanks again for all of the input and advice and for directing me to the other forum exchange. That guy built a gorgeous Jeep! 

Yes, all components are installed exactly as outlined in the Hesco guideline. The pump and regulator are mounted along the frame rail just in front of the gas tank. The pre-filter is mounted aft of the cross over next to the floor pan, where the fuel lines converge, to get it farther away from the exhaust pipe. At least now I can eliminate fuel as a cause and move on. When I get a chance to get back out in the garage I'll definitely look into the electrical issues you suggest. I agree the CPS is far from perfect and its alignment has always been a concern for me. It doesn't sit square to the damper, so getting the right gap is difficult.

I am going to check timing and get back to you. I find it interesting that the Hesco instructions specify timing should be 10-12 degrees, whereas my CJ shop manual (and sticker under the hood) specify 15deg +-1. 

Push rod length never occurred to me! I know the originals were re-used, the engine had a complete valve job and new valves installed and both block and head were resurfaced (-0.008 on the block and -0.014 on the head). Considering  this was a stock rebuild and using the same head, I never gave the push rods a thought. I'm surprised the engine shop did not check this or advise me of the possibility. If nothing pans out on the electrical side I will pull the valve cover and check the push rod length (I like the tool from Comp Cams).

To be continued next week...

Lou

 

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Hi, Lou...The CPS must be gapped to the damper properly.  Make sure you rotate the crankshaft (ignition OFF!) by hand to see whether there is runout on the damper that is impacting the crankshaft pickup gap.  Check with a feeler gauge at 90-degree points on the damper.  You may need to average the gap to meet the crankshaft damper's runout;  the goal is to be within the normal gap range specified.  The pickup cannot drag on the damper, and it cannot be spaced out too far.

10-12 degrees is for the programming in the 60-pin PCM.  You can alter the base timing slightly by tricking the computer with an offset of the CPS.  There is also a 5-degree adjustment window within the PCM that can correct for detonation/ping if needed.  You need the correct scan tool to perform this adjustment;  a Miller/SPX DRB-III tool was commonly used at dealerships.  Your CJ's OEM decal is for a conventional ignition distributor that had a centrifugal and vacuum advance mechanism.  The Mopar/HESCO spark timing system is electronically adjusted by the PCM and works from a programmed base timing.

If necessary, you can change pushrods without much effort.  The time involved is measuring the zero clearance length with the valve closed and cam lobe on its heel.  This work can be done with just the valve cover removed and by loosening each pair of rocker arms as you make necessary measurements and corrections.  Refer to my discussion with Stewart Snow at the forums.  Find TDC on each cylinder's firing cycle before measuring that cylinder's pushrod length.  (Read the rotor and crankshaft position if necessary.) 

The CompCams tool is the cost-effective approach.  You need the correct tool for your pushrod length range.

Moses 

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  • 3 weeks later...

Hi Moses.

I read and followed the information in your previous forum postings and bought the CompCams tool and removed the valve cover to check the pushrod lengths. Starting with #1 cylinder and working my way thru the firing order I carefully lined up each piston at TDC on its compression stroke making sure both valves were closed. Use of the CompCams tool is simple and straightforward. I went thru the measurement process several times since I had never done this before. Initially I tried using my old Vernier scale calipers, but it's only a 6" and I was struggling to measure the difference between my existing rods and the adjusted length of the CompCam tool. I ended up purchasing a 12" digital caliper resulting in faster, more accurate readings.

Reviewing my notes and receipts from the engine build,  .008 was removed off the block and .014 from the head. New intake and exhaust valves and new exhaust valve seats were installed; no mention of the intake seats so I assume they were ground. The pushrods were not replaced and all measured to be stock length of 9.7" plus or minus a couple of thousandths due to wear I suppose.

Here are the results of my measurements in the order of intake/exhaust with the longest and shortest highlighted in red. The bigger variation between the intake and exhaust for #1 and #5 bothered me so I checked them again with the same result.

  1. 9.585/9.567
  2. 9.571/9.570
  3. 9.548/9.547
  4. 9.556/9.550
  5. 9.577/9.558
  6. 9.565/9.558

Looking at these measurements I feel my current pushrods are too long. Even taking the longest (9.585") and adding max preload of .060" gives 9.645" which is shorter than my existing 9.7" pushrods.

So if I understand this process correctly, for a preload range of .030" to .060" would I be safe to shoot down the middle and add .045" to my measured length to acquire the required pushrod size and still have enough range on either end of the preload range to allow for the variation in length? 

Please let me know your thoughts.

Lou

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Hi, Lou...Pleased that you followed through here.  Often with head surfacing, block decking and new valve seat depths, builders will come up with your findings.  Valves sometimes do not seat completely.

Melling offers pushrods in a variety of lengths, and you could target 0.035"-0.040" to stay in the window.  The cautionary consideration is wear:  As the valve faces and seats wear over time, the valve stem stands higher in the head with a consequent increase in lifter preload.  (Simply put, when the valve wears into the seat, the pushrod gets pushed down further at the lifter end, and this increases the preload.)  This is like lengthening the pushrod.  To get the plunger to ride at a normal preload over the engine's service life, I would work with a 0.035"-0.040" preload if possible.  

Your concept of adding a given amount to the existing pushrod length is correct.  Since the CompCams tool measures the pushrod length with the rockers in position and bridges torqued, you are already accounting for the rocker arm ratio.  Lengthening or shortening the pushrod is simply preloading the lifter plunger to ride at the correct height.

Let us know how correcting the lifter preloads changes your engine's performance.  You're saving its life.

Moses

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Hi Moses. Thanks for the input. Based on my measurements, for most of the valves using a combination of the Melling MPR-301 and MPR-333 will give me a pre-load between 0.036" and 0.047". However four of them fall in between the two. See below preload for MPR-301/MPR-333:

#1E (length 9.567) 0.027/0.055

#2I (length 9.571) 0.023/0.051

#2E (length 9.570) 0.024/0.052

#6I (length 9.565) 0.029/0.057

In your opinion, is it better to be too long or too short? Alternatively, should I consider adjustable length rods for these positions?

Lou

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Lou...Ideally, you want each of these intake and exhaust clearances/preloads closer to the 0.030" to 0.040" range.  Melling pushrods are available individually, but if you can't find an "in between" length from Melling or other reman parts sources, there is a company that makes custom pushrods to length: https://www.pushrods.net/.  Not sure what they charge for a pushrod, maybe it's cost prohibitive, maybe worth pursuing.

Given the choices you pose, I would go as follows with stock-type Melling replacement pushrods:

#1E:  0.027"

#2I:  0.023"

#2E:  0.024"

#6I:  0.029"

For clarity, most OE vehicle/engine manufacturers want a 0.20"-0.040" range.  I am good with your 0.036"-0.047" range...If you have no choice in bringing these four valves to 0.030"-0.040" range, I'd cleave to the 0.020"-plus side here.  Unless you know for certain that the lifters allow for 0.060" preload, I would shy away from the deeper preloads.

Note:  For those unfamiliar with the CompCams tool, measurements are always made with the camshaft on the cam lobe heel or "base circle".  (Use of TDC on the compression stroke is accurate when the camshaft lobes are not visible.)  The lifter plunger must be fully extended ("zero lash") with no additional plunger pressure applied.  Zero lash can be felt by rotating the pushrod as you extend the threaded portion of the tool.  When the rocker arm gap closes and rotational resistance is barely felt, that's zero lash.  Extending the test tool's length beyond this point will depress the lifter plunger and create "preload".  Measure the pushrod tool length for zero lash; then add the number of thousandths of an inch of desired preload to that measurement.  When we say, 0.20"-0.040" or 0.30"-0.60", we mean zero lash plus this amount.

Moses

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  • 8 months later...

A long overdue update to my situation...

  1. Pushrod replacement. Following the steps outlined in this forum, this is not a very difficult job. I purchased the CompCams tool and a set of 12" digital calipers. It takes some practice, and I went through all of my pushrods multiple times until my readings were very close and then took an average. In the end, there are only a few pushrod lengths available for any given engine. So I got as close as I could and ordered a lenght that would work best, bearing in mind there is the 0.020-0.060" pre-load range.  There are kits available to make custom length rods if you really want the lengths perfect. However, it is a bit expensive, probably more geared to hot-rodders and racers looking for optimal performance. I did not see the need for my purposes. Though I consider this job a success, it did not solve my original problem of the engine misfiring or cutting out.
  2. Engine misfire/cut-out. Going back and re-thinking my symptoms, this continued to seem like a fuel flow issue. The engine just seemed like it was sputtering as though it was running out of gas. Having checked and/or replaced everything else in the fuel system (see previous sections of this post) I went back and looked at the basics of fuel/air induction. If the computer controls how much fuel (and its timing) to each injector, what gives the computer this information? Stepping on the throttle pedal only opens the butterfly valve to let in more air. Then it hit me that there must be a sensor which senses this flow change, sends a signal to the computer to cause the adjustment in fuel flow. Newer engines use a Mass Air Flow (MAF) sensor but this Mopar set up uses a Manifold Absolute Pressure (MAP) sensor. Now things made sense. I replaced it and my problem was solved. Always something new to learn.

I hope this info helps someone else down the line.

Lou

 

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Excellent, Lou.  You now have the correct pushrods and have eliminated the misfire with a new MAP sensor.  Nothing lost here.  And you're way up the learning curve!

I'm investing time this year in sharing a PicoScope and diagnostic tools that read the function of sensors like MAP in live, real time.  I thought of investing in a high end scanner and have used the noteworthy Miller/SPX DRB-III tool that gave Chrysler dealers a diagnostics edge.  What you discovered is true for all diagnostics:  devices fail

The PicoScope can read electrical/electronic activity in wave forms and doesn't require proprietary programming like factory scan tools.  The DRB-III last sold for $6,000 and is reselling used for $2500-$3000 at eBay.  PC-based oscilloscopes can test the same devices for far less cost.  The Hantek 1008C and Autel MP408 oscilloscopes are quite affordable.  The distinction among these devices is the manufacturer's software.  Here, Pico has the advantage.

Congrats...Good diagnostic work and an engine that will have a safe and smooth valvetrain throughout its service life.  Your HESCO/Mopar EFI Conversion does have a diagnostics plug, though it's OBD (1) era.  You should have a stored code if a device like the MAP sensor fails.  Code reading is much easier with the later OBD-II PCMs, though your 60-way PCM will store DTCs.  Some install an LED lamp at the dash, triggered off the diagnostics wire.  Check you wiring schematic for the EFI kit, it should show a lead for the DTC Engine Check Lamp (MIL).

Moses  

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