jj_jeep

4.0L Jeep Six: Cylinder #1 Misfire Trouble Code

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Thanks again for the input. I had read the post from 2008 and have considered replacing the TPS and CPS with Mopar components. As for the capabilities of the scan tools I can borrow, I honestly don't know. As soon as I do more checks I'll post it. Again, thanks for your time and suggestions. Will advise.

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Unless your CPS was damaged from being loose, I would begin with the TPS switch. You can check the ohms-resistance on the CPS if you're concerned. I have specs if you need them, Bamafan1!

 

Moses

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Well, I was going to do the TPS first then CPS. The only reason I mention the CPS too is that fact that it was loose nor know if it's the original or not. If it was replaced with an inferior product then who knows. As for any spec's I'll always be glad to get any info possible.

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A footnote on the CPS: The stick shift models have a conventional sensor with a pre-set depth on the probe/pickup. Automatic transmission models use an adjustable pickup (single bolt unless 2.5L, which uses two nuts instead of bolts) that requires a paper gap and fresh start-up depth for the sensor pickup. The gap is established using Mopar part #05252229 paper spacer for initial depth setting. The paper spacer tears off as the drive plate rotates.

 

The CPS and notches on the flywheel or drive plate are essentially a hall effect switch with sync and signal generator phases. Again, proper pickup gap is important on automatic transmission applications, if too close, the pickup will be damaged as the engine cranks. If you have a manual transmission, the CPS pickup depth does not require adjustment.

 

My Mopar manuals simply say that the CPS should be tested with the DRB-III scan tool or to refer to the "Powertrain Diagnostics Manual". Essentially, this magnetic core sensor pickup either works or doesn't work. If mounted correctly, with the right pickup depth, the CPS should work—or not, in which case you will get a MIL, even with just engine cranking.  That's the test...Unless the CPS probe is physically damaged, it should work.

 

Moses

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I've got a manual transmission. Is it safe to assume the CPS would have a separate code? I'm assuming it's functioning properly, but I'm not sure what, if anything, the previous owner may or may not have replaced. I've decided that I'll try a new TPS and ask if I can return the CPS if unused/uninstalled. At least that way I can compare what I've got vs. what should be.

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"No Crank Reference Signal" is a Code #28.  This would be the CKP or CPS signal during engine cranking, so yes, there is a distinct code.  Code P1398 is a "No Crank Sensor Learn" code.  Both would be indications of a possible crankshaft position sensor fault.  If you try the TPS by itself, first, you can separate the issues and pinpoint the possible cause of trouble.  That, of course, is if the P0301 DTC decides to go away!

 

When you install the TPS, be careful about winding tension to the normal baseline position.  Use care, you'll see the relationship of the parts.  Let's see what this does.  If nothing else, you're replacing an obvious wear item in the EFI/MPI fuel and spark management system, and that's useful.

 

Moses

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I don't see where you mentioned the year of your Jeep, so this may or may not be relevant.  I have a '98 XJ with the 4.0.  When I bought it, it had a slightly rough idle.  No biggie, a good tune-up will take care of it.  Over the next couple weeks, I pulled my hair out as everything I checked failed to reveal the cause of the P0301.  At my wits end, I stumbled across a TSB that covered, I believe, '96-'99 4.0s.  It said that if you had a misfire and all other possibilities had been eliminated, you are to run Mopar Combustion Chamber Cleaner and replace all the valve springs.  (I suppose a weak spring could cause the misfire, plus allow carbon buildup, therefore requiring the CCC).  I ran the CCC and replaced the springs on just cyl 1.  Problem solved!  Again, this might not be your problem, but just wanted to throw it out there.

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It's a '98 with a 4.0, manual. I have Seafoamed but not used Mopar product. As for the valve spring, I considered that based upon some advice and forums. However, idle doesn't seem rough (rpm's are constant when sitting still). Also, I've been lead to believe I'd hear noise too. How difficult is it to replace a valve spring?

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There wasn't any unusual noise, but I did have a slightly rough idle.  I used the old "rope method" (moved the piston down, slowly stuffed a new nylon rope into the spark plug hole, then turned the engine by hand until the piston was up as far as it could go).  Then I used a spring compressor that pivoted on the rocker arm stud.  A couple tips for replacing springs: replace the valve stem seal, and use a magnet to catch the keepers when you compress the spring and grease to hold them in place when re-assembling.

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Thank you for info. Unfortunately, I'm not that experienced to do alone (nor do I have all the correct tools). Maybe I can find a video or step by step instructions. Again, thanks for the advice.

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I'm pleased to see you jump into this, Belvedere, great suggestions!  Regarding weak valve springs, they can show up in a simple manifold vacuum check.  At any steady throttle setting, there will be an erratic, shaky vacuum needle movement with the vacuum gauge hooked up to an intake manifold vacuum source.  (Not to be confused with the wider swinging needle movement associated with a valve that is steadily leaking.)  As you share, Belvedere, weak valve springs can build up carbon, as the valves do not seat firmly when closed.

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Valve springs can actually be tested for valve seat pressure on the engine.  Above is a photo of a simple tester available for that purpose.  (Click here for a more upscale Moroso 62388 design available at JEGS.)  With the rocker arm(s) removed, head and valves still in place, this over-the-top spring pressure tester can indicate the actual seating pressure, which is a true test of each valve spring's function.  This is a sensible testing method with the least amount of teardown work: simply removing the valve cover and rotating the crankshaft to close the valve(s) to be tested.  (Caution: Disconnect the negative battery cable to prevent starter engagement when turning the crankshaft by hand.)

 

There are two off-the-engine tests for weak valve springs.  If Belvedere still has the original springs, measuring and comparing the free standing height of the springs can be one test.  Another method, commonly used by automotive machine shops and race engine builders, is actual spring compression testing (read in actual pounds force or as PSI) with a special gauge.  This measures pressure as the spring compresses. 

 

As for removing the valve springs, Belvedere's method works.  So does an air hold, and this is especially easy for #1 cylinder, since the timing mark for TDC on the crankshaft damper is a quick way to find TDC for #1 piston. 

 

Here's how I do an AMC-design Jeep 4.2L or 4.0L valve spring removal:

 

1) Disconnect the battery negative cable to disable the starter.  Remove the valve cover and spark plugs, at least #1 plug in this case, all of them to make rotating the crankshaft easier by hand.  Rotate the crankshaft by the damper bolt, turning the crankshaft in its normal direction of rotation.  Watch the valves open and close to be sure #1 piston is coming up on its compression stroke as you bring the damper pulley around to TDC on the compression stroke.

 

2) Set the damper mark at TDC to be sure the #1 piston is at the top.  This will prevent fears of "losing" a valve into the cylinder.

 

3) Use an air hold fitting in the #1 spark plug hole to keep the valves up in position.  These adapter/tools are commercially available and inexpensive, or you can make an air hold tool with an air coupler and an old spark plug.  (See my comments below.  Summit Racing lists the KD 901 adapters for $4.97, the best price I've seen anywhere!  For that price, no need to make your own.)

 

4) Remove the #1 cylinder intake and exhaust rocker arms.  The pedestal bolts simply get torqued back into place, there is no valve "adjustment" to be concerned about when you reassemble the rockers.  (Just align the arms carefully with the pushrod tips and valve stems when you reinstall the rocker arms.)

 

5) With a stream of air applying pressure from any reasonable size home shop or garage air compressor, you can remove the valve springs using the "over the top" method.  (80-90 PSI should be plenty, there will be some leak down, so your tank compressor should be full when you begin the spring change out.  You can recharge the compressor if necessary between each spring removal.)  Belvedere's approach with a pry tool attached to the rocker stud can be effective, and this tool is readily available.  KD has made an affordable rocker pedestal pry bar for many years.  Even if "universal" fit, however, make sure the tool is designed for the Jeep 4.0L engine application, or you will be fighting this task.

 

6) There is also an over-the-top valve spring compressor available, which can be easier to control for the less practiced mechanic.  (OTC's version is shown at the Summit Racing page link.  KD makes a tool like this, too.)  This is a two jaw compressor that can compress the spring between the valve spring retainer and the spring coils.  This tool is great—as long as there is enough installed spring height and adequate coil gaps for the jaws to fit.  You must be able to compress the spring enough to safely remove the valve keepers.  With either tool, stay centered on the valve spring retainer to prevent valve stem or keeper damage, and carefully remove the keepers like Belvedere cautions.  Belvedere's magnet suggestion works.

 

As a valve hold, Belvedere's traditional rope method certainly would work.  (I like that vintage Mopar logo, Belvedere!)  Make sure the piston is coming up on the compression stroke before inserting the rope.  Otherwise, rope could get caught between a valve head and seat, which would reduce exposed valve stem height (or chew up the rope under valve spring pressure).

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As for making an air hold tool, above is a photo of the hold I made in ten minutes for a tight-access Honda four-valve motorcycle engine.  The KD type adapter is so inexpensive that unless you need the tool this minute or have a unique situation (like the narrow access Honda four-valve thumper motorcycle engine, which will not accommodate the air hold adapter!), buy the KD or similar air adapters.  

 

Steps involved in making and using an air hold tool:

 

1) Remove the ground strap from the old spark plug shell.

 

2) Knock the porcelain and center electrode out of the plug shell.  Use eye protection, you're breaking porcelain/glass here.

 

3) If the shell size allows for tapping with a pipe tap, you can drill, cut and thread for an air coupler fitting's male threads. 

 

4) Use Teflon tape on threads of the air coupler fitting if you do use the threaded method.  I find brazing works very well and can be a much quicker way to attach the air coupler fitting—if you have an oxy-acetylene welding/brazing torch. 

 

5) Surface grind away any rough areas, like the remainder of the ground strap weld.  Wire brush your "new tool" as required.  You don't want loose material to blow into the engine's cylinder.

 

6) Thread your KD type or homemade tool into the spark plug hole. With the piston at TDC and the valves closed, hook your hose coupler to the air fitting and apply compressed air at the fitting and into the cylinder.

 

The air hold tool is a way to hold the valves in position and also run a crude cylinder leak down test.  (For details on a leak down test, see my HD video how-to at the magazine site.)  Though you cannot measure the percentage of leak with an air hold adapter, you can certainly find a badly leaking valve or leaky piston rings by the volume of air leaking out of the cylinder through the exhaust pipe, intake manifold/throttle body/carburetor or into the crankcase.  The leak down test is only reliable when performed with each piston at TDC on its compression stroke and both valves closed.

 

That the PCM would send a #1 Cylinder Misfire DTC, code P0301 in this case, due to weak valve springs is "interesting". The diagnostic tie-in here would be incomplete combustion, since fuel flow volume through the injectors is uniform (whether the valves seat properly or not), and the ignition spark reliability can be easily determined with an oscilloscope analysis.  Poor injector flow or weak spark can also create incomplete combustion and a misfire.

 

So, that means that the DTC reflects poor combustion at #1 cylinder, which could also be the result of inadequate valve sealing from the weak springs.  AMC-design engines do not have a history of weak valve springs, so weak valve springs should not be an epidemic or wide-ranging concern.  However, it would be a factor in some cases, and "weak valve springs" can result from valve seat recession/wear, overheated valve springs or over-revving the engine to the extreme and "floating the valves".  The 4.0L and 2.5L engines are known to run 250K miles without valve spring issues.

 

Belvedere, thanks for sharing.  This kind of information is very helpful to the forum members!  I'm very pleased that you take time to contribute at this level!

 

Moses

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Great write-up, Moses, with lots of explanation/details.  I like your instructions for the home-made air adapter!

 

It was interesting reading about the tool designed to test valve springs on the engine...I hadn't seen those before.  I was going to take the springs to my local machinist to test, just out of curiosity, but never got around to it.  Maybe I will yet.

 

Like I said, according to the TSB, this applies only to a few model years.  I wonder if Chrysler had changed the valve spring design for some reason, or the supplier was different, or ???

 

My understanding of the PCM detecting the misfire is that it uses the CPS to detect a change in the momentum, or speed, of the rotation, and also, depending on when in the rotation this happens, can detect which cyl is causing it.  (I hope I didn't make that too confusing or unclear!)  Honestly, I can't remember where I got that info...hopefully I read it somewhere, and didn't just dream it up!  ;)

 

Jeff

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Thanks, Jeff...Interesting comments about the CPS function. This is a hall effect system and is fairly straightforward. The notches in the flywheel or flexplate and the pickup provide a precise location for the #1 cylinder TDC position (actually the pulse output is 4-degrees BTDC on the 4.0L and the PCM calculates TDC from this generated signal).  The rotating, notched flywheel/flexplate and the magnet in the CPS probe generate the pulse signal. 

 

Mopar defines the CPS function as:

 

"This sensor is used to indicate to the [PCM] that a spark and or fuel injection event is to be required. The output from this sensor, in conjunction with the camshaft position sensor signal, is used to differentiate between the fuel injection and spark events. It is also used to synchronize the fuel injectors with their respective cylinders..."

 

The CPS would help the PCM sense minute fluctuations of speed caused by a misfire. Why the constant reference to #1 Cylinder on bamafan1's engine is interesting. While fluctuation could be caused by a misfire at any cylinder, there seems to be an epidemic of #1 Cylinder Misfire codes out there, suggesting something other than a local (#1 cylinder only) misfire.  

 

If this code is always valid and really does include weak valve springs at #1 cylinder, as in your experience, the only thing I can add is that #1 cylinder is usually the hottest running cylinder in an inline six. That could fatigue the valve springs earlier on #1 than other cylinders. We can test and confirm this with a simple surface thermometer, comparing #1 cylinder's temperature to the other cylinders with the engine hot. A good place to probe heat would be the cylinder head surface at the spark plug areas or the upper cylinder and head mating areas. Let's see what comes up! 

 

Regardless of how the PCM determines a misfire, the cause of a true misfire (not just a false signal) would be mechanical. In my view and experience, this could be caused by a variety of factors, here are a few quick prospects:

 

1) Ignition malfunction including spark wire breakdown, corroded rotor tip or distributor cap contact resistance

2) A lean or rich fuel mixture, more likely lean in the case of electronic fuel injection, especially multi-point MPI with an injector for each cylinder (much easier to determine air/fuel ratio per cylinder than with a carburetor or TBI, which feeds all cylinders through an intake plenum)

3) Low compression, which could be caused by poor ring seal or leaky valves

4) Ineffective or erratic spark timing advance, which could involve several sensor signals like the MAP, coolant temp, intake air temp or mass air flow in a MAF system

5) Vacuum leaks at hoses or the intake manifold junction with the head—good idea to re-torque the intake manifold, we haven't done that yet! 

6) Exhaust gas recirculation valve issues: EGR unseated, sticky, fluctuating, fluttering, take your pick.

7) Oxygen sensor or catalytic converter issues, or a restricted exhaust system

8) Crankcase ventilation issues in a PCV system

9) Out of sync crankshaft and camshaft position sensors (worn timing chain, distributor installed improperly, distributor timing position off). This could send a camshaft position sensor fault code, or maybe not if the issue is tottering.

 

The borderline camshaft/crankshaft sync problem could be a loose timing chain issue. This would not be surprising for higher mileage engines. If forum members are curious, I can suggest a quick test that I've used for years to measure timing chain wear. The method is accurate enough to rule out a major problem with the chain.

 

Each of these misfire sources has its cause, and we can drill down to confirm. I like to find actual problems, and I'm sure bamafan1 would like to see his MIL light go out. We'll keep after this...

 

Moses

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Just a brief note I don't think I mentioned previously. When the mechanic and I were doing the various checks (compression, intake manifold leak, swapped injectors, etc.) we originally pulled #1 & #2 plugs. #1 was not warm, but sparked fine. #2 was warm, not impossible to hold, but warm enough. I haven't replaced the $120 Mopar TPS yet because of the recent valve spring conversation. I don't want to waste $120 by installing it as I'll need that $$ to have the valve spring replaced. Unfortunately, due to my lack of engine knowledge and tools I'm probably going to have to take this to a dealer to finish diagnose. Any idea what that might cost?

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Like your idea of sparing the $120 for a new TPS, bamafan1. As a alternative, the Auto Zone version (purchased on a weekend when Mopar parts were unavailable) was a fraction of this pricing and has work well to date.

 

The cooler #1 spark plug could be revealing, bamafan1!  What was the cranking compression on #1 cylinder? A colder plug (un-fouled and still firing) is not a good sign, usually indicating low compression or incomplete combustion.  It can also indicate an fuel air-fuel mixture error, typically running rich, which has a cooling effect unless the plug actually reaches the point of fouling out. A fouling plug is equivalent to retarding the spark timing. With low compression or poor cylinder seal (including the weak valve spring possibility with the engine running), modern engines can still clean off a spark plug due to the high spark voltages available.

 

Worth noting, the traditional oscilloscope engine analyzer's spark firing test is very valuable. The scope's ability to assess each cylinder's relative compression and its combustion pattern can be revealing. When you replace all of the ignition parts (even more parts if we follow the OBD-II DTCs!) and still have a cooler plug, this could appear as a weak cylinder firing line with the engine running. Differences in spark plug firing line height, especially after installing fresh tune parts like you have already done, can reflect variations in the combustion efficiency between cylinders!

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Scopes like my vintage Sun 720 will even perform a "dynamic compression check", shorting out each plug wire (engine at an idle) and comparing the drop in engine rpm as each cylinder goes off line. (This might be more difficult with an MPI engine designed to compensate and restore the idle rpm. There should still be a momentary rpm drop before the idle air control kicks into play.) Eliminating spark to a low compression (or poor combustion) cylinder will barely change the engine's idle rpm. 

 

Also, simply "blipping the throttle" while reading the spark firing lines on an oscilloscope analyzer will show firing line changes (i.e., compression irregularities) as the engine load increases. On a scope, throttle "snapping" is a realistic test for low compression because it takes into account the engine load. This test quickly turns up weak valve springs, too, as a quick speed change will exaggerate the valve spring issue.

 

Note: Jeff (Belvedere) is likely onto this one...We used to idle the engine and pull individual spark wires with an insulated spark wire pliers (at each plug wire's insulator to prevent damaging the wire!), noting the rpm drop on a tachometer. This is essentially the same test as the scope's "dynamic compression test" though not as sophisticated. (Again, the Idle Air Control function on EFI/MPI makes this test more challenging.) If a given cylinder, like #1 in this case, shows little or no rpm drop, there's either low compression, a limited fuel supply (with MPI) or poor combustion.

 

Is this time for a leak down test or at least an "air hold adapter" test at #1 cylinder? The $4.97 adapter and 80-90 PSI of compressed air into the cylinder at TDC on the compression stroke could suffice as a quick leak check. (No percentage reading, of course, but if there's a substantial compression loss/air leak, you'll find it quickly!) A quick interpretation of air leakage would be:

 

1) Leaky intake valve will be audible at the intake. Open the throttle to hear the air leak better.

2) Air exiting the tailpipe is a leaking exhaust valve.

3) Air entering the crankcase would be audible by simply removing the oil fill cap. This air leakage would be blowing past the piston rings.

4) A compression/air leak loss between two adjacent cylinders is typically a blown head gasket. Bubbles in the cooling system can also be a blown head gasket (into the water jacket). Warning: If you suspect a leak between the cylinder combustion chamber and the engine's cooling ports, drop the air apply pressure to below 20 PSI—or you could damage the radiator or blow off the radiator and heater hoses!

 

If you have an air compressor, optimally with an air tank, this quick air leak test with #1 piston at TDC on the compression stroke might help demystify the #1 cylinder's condition and firing capability. A limitation is the static engine not spinning or changing speeds. A running engine is a better check for weak valve springs.

 

OBD-II and handheld diagnostic scan tools are now the alternative to traditional diagnostics methods. OBD-II DTCs, as we've discovered in this ongoing #1 Cylinder Misfire P0301 chase on the Jeep 4.0L engines, are not failsafe. By contrast, the once popular Sun 720 engine oscilloscope analyzer featured a vacuum gauge, timing light with built-in advance, leak down tester, combustion analyzer with A/F meter and other tools, each mainstays for pinpoint engine diagnostics.

 

Unfortunately, most vintage oscilloscope engine analyzers like the Sun 720, which featured a wide array of functions in one machine, have been sold off to vintage car museums as memorabilia! As you would suspect, I've kept my late 'sixties "muscle car era" Sun 720 machine...

 

Moses

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I bought the Mopar TPS in lieu of "aftermarket" because of the general sensitivity of the 4.0. As for the coolness of plug #1 as testing proceeded it did eventually warm up. When we checked compression we did it on #1 & #2 only. #1 was between 120-125psi, #2 was between 130-135psi. According to Mitchell1's website, compression should be 120-150 (discovered that after compression test). As for head gasket, I don't think that's the issue. Radiator is full as is reservoir and neither have been touched since I took ownership 27 months ago. So, all that being said, I'm back to my original dilemma: I don't have knowledge or tools to continue on my own and am concerned if I take it to a shop or dealer I'll spend unnecessary $$.

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I would rule out the head gasket, too, Bamafan1. If the gasket were leaking between cylinders, you'd have very low compression in both #1 and #2.  If leaking from #1 into a cooling port, you'd have both a loss of coolant and an over-pressurized cooling system.

 

120-125 cranking PSI is not exceptional for a 4.0L.  Before borrowing trouble here, and to save you every expense we can, you might try my inexpensive tests, offered in the last few exchanges.  In particular, if you do have an air compressor, even a home garage variety for airing tires, try the cylinder leakage test, at #1 cylinder/TDC compression stroke, with the $5 adapter. A manifold vacuum test with a simple vacuum gauge might also prove revealing.

 

What you generally want in any engine is no more than 10% variation between the highest and lowest cylinders' cranking compression.  Following this logic, if #2 were 135 PSI and #1 is 120 PSI cranking compression, that in itself could be a difference tottering near 10%.  If your higher cylinders were, say, 140-145, with #1 at 120-125 PSI, that would be enough for the engine to run roughly, maybe even send a #1 Cylinder Misfire DTC. A 25 PSI variance has always been considered a problem for both tuning and delivering good performance.

 

We may be looking at that kind of cause here, in which case, I have a simpler suggestion. If the engine has decent oil pressure, does not burn excessive oil, has reasonable power, and is maintaining sufficient fuel efficiency, let this go for now.  To troubleshoot a tuning or fuel-and-spark issue on any engine presumes that the engine is in good condition at the onset.  I have four criteria that work for me before looking for tuning problems:

 

1) Normal oil pressure (good bearing clearances, oil pump, etc.)

2) Normal compression and cylinder seal (piston rings, valves, head gasket, etc.)

3) Normal valve timing (good timing chain and sprockets, etc.)

4) Normal valve lift (camshaft lobes normal, lifters holding and not bleeding down, etc.)

 

If any of these factors are not right, then tuning or cancelling a DTC like the #1 Cylinder Misfire will be a tail chase. 

 

Your engine in stock form approaches 9:1 compression (8.7:1 on paper, without carbon buildup).  To put that into cranking compression terms, an engine with 8.7:1 to 9:1 compression and a stock camshaft profile would have a cranking pressure in the neighborhood of 155-160 PSI.  According to Mopar, you should pick this pressure up within "three revolutions" of the crankshaft, not after cranking each cylinder for 10 seconds or more!  (Either remove all the spark plugs or disconnect the coil lead from the distributor cap to prevent the engine from starting!)  Make sure the throttle is open to admit a full air charge as you crank.

 

Be aware that the listed cranking compression in shop manuals generally follows the engine's OEM standards.  The Mopar manuals typically reflect "acceptable compression" for engine warranty purposes.  This also applies to "normal" oil consumption, where most engines of a given type might use little or no oil between 5,000 mile change intervals, but for warranty claim reasons, it's "acceptable" to use a quart of oil in 2000 miles or whatever. 

 

It is always assumed that a difference of 25 PSI between the highest and lowest cylinder is an engine running unevenly.  This could easily translate through the PCM as, like Belvedere suggests, a "misfire" at the weak cylinder.

 

I wouldn't lose sleep over this redundant P0301 DTC in your case. As long as your Jeep 4.0L engine is running okay, it's money in the bank.  I would not rush off to remedy the problem until you are ready to rebuild the engine, if you ever do.  We can continue to kick the P0301 DTC around, I'm pleased to do so, but if the cranking compression is 120 PSI on #1 cylinder, I'm suspect that we'll not make a lot of headway.  And as long as the Jeep is reliable, let's be happy that you're not spending needless money on it.

 

If my hunch is correct, you will likely find a high percentage of cylinder leakage at #1 cylinder. This can seem alarming, even justification for rebuilding the engine—and it often is. If the cause is "just" carbon buildup, the Seafoam fix or a similar remedy can sometimes be a "cure", at least short term. Carbon buildup is seldom an isolated event, though. There is generally valve, ring and cylinder wear, too. Actual mechanical wear or damage cannot be remedied by de-carbonizing the combustion chambers and valves with a cleaning agent or method.

 

It's also worth noting that some engines maintain functional cranking compression and run reasonably well despite showing a high percentage of cylinder leak down. These engines can go many miles without creating a problem, and they cost no more to rebuild later than now. Again, it goes back to the four basic engine needs and whether each need is sufficiently met—at least enough to postpone a costly engine rebuild.

 

Note: My approach with these posts is to not spend others' money needlessly. Sometimes, we're postponing the inevitable. This Jeep 4.0L #1 Cylinder Misfire P0301 DTC is a case where we need to confirm the engine's basic condition before attempting to "tune out" the problem. Our troubleshooting, in any case, needs to begin with confirming the four basics. Once we know the engine's basic "long block" condition, the rest is either chasing vacuum leaks, tuning or replacing defective parts that the PCM or an OBD-II scan tool might—or might not—turn up.

 

Moses

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Moses, please note that I do not nor have felt that any suggestions were provided by you or anyone else to just spend $$. As for your criteria I think #1 and #2 (of your criteria) are good. Oil gauge has held same position since day one. #2 I think is good to based upon earlier check. That being said, unfortunately I don't have the skills, knowledge, or tools to confirm or deny #3 or #4. Any chance you could come to Alabama and instruct me in person? (just kidding, as I realize that's not feasible)

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Just clarifying, bamafan1, there's always the "throwing good money after bad syndrome", and we don't want to waste money on tune parts when the engine is worn significantly. If we begin with the four engine basics, we can determine whether the engine is in "tune-able" condition. This #1 Cylinder Misfire code could border between a tuning issue and engine wear. Lower compression and compression variation between the highest and lowest cylinders might trigger this DTC code. Engine wear needs to be considered.

 

As for the #3 and #4 (valve timing and valve lift) basic engine needs, there are simpler rough tests for these two concerns. First, if you have an engine with timing chain wear, the valve timing is retarded.  So, assuming that the timing is not bad enough to have the chain jump a tooth, we can make a rough determination of whether the valve timing is retarded much.  Here's the quickest check possible:

 

1) Battery negative cable disconnected to disable the starter and ignition, note the #1 plug wire position on the distributor cap and remove the distributor cap.

2) Rotate the crankshaft in the normal direction of rotation and slowly approach the TDC mark on the compression/firing stroke. The rotor will be pointing toward #1 plug wire position when you stop at the TDC mark on the crankshaft damper. 

3) Now, very carefully watch the rotor as you slowly rotate the crankshaft in the opposite direction of rotation.  Note the exact point where the rotor begins to move.

4) At the outside diameter of the damper, measure how far you have rotated the crankshaft pulley/damper.  (Try to estimate the number of degrees based upon the degree marks on the damper.)  If you measure 3/4" or more of outer pulley movement before the rotor begins to move, on a pulley of this diameter, there's a lot of play in the timing chain and sprockets. 

 

Note: This is not a pinpoint test for chain and sprocket wear, but without removing the timing cover, this will provide a rough idea of whether the chain is too loose. If so, the valve timing is retarded. On an OBD-II system with both a crankshaft and a camshaft position sensor, there is a built-in check for the sync between these two readings. Theoretically, if the valve timing is too lagging, the camshaft position will be out of sync with the crankshaft position. A DTC should appear...if so, a loose timing chain could be at fault.

 

As for the valve lift, this is a bit more involved, as you need to remove the valve cover, and you need a dial indicator with magnetic stand:

 

1) Remove the valve cover and rotate the crankshaft with a socket and ratchet as you did for valve timing, with the battery negative cable disconnected to prevent starter engagement.

2) Bring #1 piston to TDC on the firing stroke (easy to determine as the valves will both be closed as the piston rises).

3) Set up the dial indicator plunger above the #1 exhaust valve's pushrod and rotate the crankshaft slowly to reach the highest valve opening point. If you have measured directly above the pushrod, you are measuring the lifter or camshaft lobe lift

4) This measurement indicates how much the camshaft lobe has raised the pushrod. Actual valve lift is similar, you measure at the rocker arm directly above the valve stem. Valve lift takes into account the rocker arm pivot ratio.

 

If you want the valve lift test to be more accurate, measure the actual valve opening in 1000ths of an inch of valve lift. Compare this with the camshaft and rocker arm lift specified for a stock Jeep camshaft. (I can provide a figure if you do this test.) You can check and compare the lift at each of the twelve valves, measuring from a closed position to a fully opened valve. 

 

The concern here is whether a valve lifter is badly worn (you'd likely hear it as valve clatter) or a camshaft lobe(s) are flat. Jeep 4.0L camshafts and lifters do not have a bad record in terms of lobe and lifter wear.  Many engines do, though, including a large number of small- and big-block Chevrolet V-8 engines "in the day" that had OE camshaft lobes go flat from poor billet material. Typically, a Jeep camshaft and lifters get replaced on a higher mileage engine during a rebuild. The chain and sprockets always get replaced.

 

I would not be as concerned about the valve lift, though it could create the misfire issue if lobes and lifters have significant wear. The timing chain is another story, though. Any Jeep 2.5L four or 4.0L and 4.2L inline six with higher mileage can use a new timing chain and sprockets. Again, unless this will make a significant change in overall engine performance or prevent a catastrophic event like an extremely loose timing chain jumping teeth and slamming the valves into the piston heads, wait until the engine rebuild to address a worn chain, sprockets or lifter/camshaft wear.

 

My first move at this point would be the cylinder leak down test performed on #1 cylinder with the piston at precisely TDC (highest ring and cylinder wall wear point in the cylinder) and the valves both closed (on the compression/firing stroke). Pinpoint the leakage, with 120-125 PSI cranking compression, there will be cylinder leakage. Also, I would check the manifold vacuum at an idle. Retarded valve timing, like retarded spark timing, will show up as low manifold vacuum readings at an idle.

 

Moses

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I've been following the thread with interest and thought I would offer a quick update on my Jeep... I get an occasional MIL for a cylinder 1 misfire, but I don't actually notice the misfire (if there truly is one) like I did when the bad injector was in there. And when the Jeep started at the end of the work day yesterday when it was -15 air temp, I feel pretty good about driving it for a while! it idles a little rough, but at 253k miles, I can accept that as long as it's not stalling (which it isn't).

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Great to hear your update, JJ_Jeep!  Sounds like high mileage does play a role with the #1 Cylinder Misfire DTC.  We're back to basics, and I'm glad the discussion went full circle to addressing underlying engine condition and wear factors...DTCs are obviously more precise when equipment is newer.

 

Pleased that your Jeep starts at -15 F and your heater works!  I use a block heater below 40-degrees F as a means for keeping the engine bearings in good condition. 95% of engine bearing wear is at startup.  Keeping the crankcase warm helps offset startup wear—and the heater is functional within a few blocks of driving! 

 

You know, we're talking about vehicles with real use, and given the cost of a new replacement Jeep, or even a thorough engine rebuild or crate motor, every day we can drive these vehicles safely is money in our pocket—they can only depreciate so much and are most likely at or near their lowest price point by 150K or more miles. 

 

Our 1999 XJ Cherokee 4.0L 4WD has 145K miles and still runs very well and quite reliably.  (We bought it stone stock and in "good used condition" at 94K miles.)  It would be ridiculous to dump the XJ now, as these vehicles, maintained properly, can often reach 250K miles, like your TJ Wrangler, without a whimper. 

 

I'm grateful for my background as a professional mechanic and grateful for good mentors and broad based learning opportunities along the way.  Over the decades, it's saved our household a small fortune in vehicle expenses—and lost dollars in new vehicle depreciation, which can be substantial.

 

Happy to help keep the high-milers running safely and reliably...We'll focus on "reality checks" for openers and start our troubleshooting with a solid assessment of the engine's basic condition...

 

Thanks for sharing! 

 

Moses

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I'm back with a dumb question. After driving my jeep if I remove the distributor cap should the rotor be near/pointing close where plug wire #1 connects to the distributor?

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At these forums, there are no dumb questions, Bamafan1! 

 

On a four-stroke engine like your Jeep 4.0L, the distributor shaft and rotor turn at 1/2 the speed of the crankshaft.  When the distributor shaft and rotor are set in position properly, the #1 piston will be at top-dead-center (the firing position) when the rotor points toward the #1 spark wire in the distributor cap.

 

As the crankshaft turns, so does the rotor.  The rotor, turning at 1/2 the speed of the crankshaft, will point to each cylinder's spark wire position only when that cylinder's piston is up to fire. 

 

The timing mark on the crankshaft pulley damper helps us set the rotor position for #1 cylinder's piston up to fire.  Important to note, the cylinder opposite #1 in the firing order (#6 cylinder for your 4.0L inline six, will also align to fire with the damper mark at TDC.  If you have the cylinder head off, you will see that when #1 piston (cylinder at the front of the engine) is at the top of its cylinder, so is #6 piston (cylinder closest to firewall).  Your engine's firing order is 1-5-3-6-2-4 with #1 and #6 pistons moving up and down in sync. 

 

The rotor is driven by the distributor shaft; the distributor shaft drive gear is driven by teeth on the camshaft; the camshaft sprocket is driven by the timing chain; and the timing chain is driven by the keyed crankshaft sprocket.  When you shut off the engine, the rotor will be aimed in relationship to the position of the crankshaft and camshaft.  This could place the rotor in any of its 360-degrees of rotation.  The engine's crankshaft coasts to a stop somewhat randomly. 

 

If you want to know where the rotor should point for timing purposes, this position is always in relationship to #1 piston at top-dead-center ("0" degrees or TDC mark on the crankshaft pulley/damper) on its compression stroke.  A common error when timing a four-stroke engine is to set the crankshaft at TDC mark with #1 cylinder's piston at TDC on its exhaust stroke.  This would have #1 cylinder firing 180-degrees out of time at the distributor.  The engine will not run and usually backfires badly while cranking. 

 

Keep in mind, on a 4-stroke engine, the crankshaft turns two full revolutions for each one revolution of the distributor's rotor.

 

Trust this helps, Bamafan1...

 

Moses

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Just out of curiosity, what should happen when you unplug the IAC. Not remove it, just disconnect it. Also, what is the part near the rear of the intake manifold, it sorta looks like a brass pipe plug? What should happen when you unplug it as well? Both questions are related to when the engine is running at idle.

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The IAC is the idle air control.  Disconnecting it should affect the engine idle speed.  A defective IAC shows up as an unstable idle speed, with the idle hunting up-and-down, unable to maintain a stable engine rpm.  The IAC in good operating order will maintain a steady idle speed, even as engine load changes.  This is why EFI engines are so well suited for rock crawling:  They don't stumble and stall as engine load increases unexpectedly, which occurs with a conventional carburetor.  With EFI/MPI, the idle air control needs to function properly.

 

The device in the picture looks like your IAT.  This is the idle air temperature sensor, which is part of the air-fuel and spark management system.  Idle air temp tells the computer (PCM) the actual temperature of incoming air.  This helps determine the fuel injector pulse width.  Pulse width determines the volume of fuel that flows through the injector.  Cold air during warm-up is an important signal, as is the coolant temperate (CTS).  Warmed up, the incoming air requires a different injector pulse width.  The IAT (intake air temperature) sensor is important.

 

Both the IAC and the IAT play important roles with engine fuel and air mixture settings.  The IAC adds just the right amount of air to a given fuel supply in order to maintain a specific idle rpm.  The IAT is a sensor that sends intake air temp signals to the PCM.  IAT signals give the PCM "information" required for properly regulating the injector pulse width and fuel flow.  The oxygen sensor (O2) reads actual oxygen content in the exhaust, after the combustion process.  This information is also very important for setting air-fuel ratios.

 

Moses

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