What brand crank and cam sensors did you use?

 

Did the issue start after the engine was installed? If so, how long after? Have you checked the vacuum lines for cracks?

 

I had trouble sourcing Mopar sensors. The CPS is Hitachi and the CSPS is Tamkken.

The troubles started with about 5000 miles on the engine. It ran fine all Winter and started acting-up last Spring.

 

Get your compression and spark testers ready…drive it until it screws up…then check compression first, then spark.
something as stupid as a lifter collapsing hot?? Or coil driver giving up after it warms up.
Reman engines make the hair stand up on the back of my neck.

this is my go-to spark tester. (Dang they got expensive!!)

 

Especially JASPER reman’s!! I know, I had 3 of them(4.0L) in 2 1/2 years. And this 3rd engine, with less than 8,000 miles on it showing very high levels of lead and copper in 4 consecutive Blackstone Lab oil analyses. But that’s a whole other NIGHTMARE for another discussion.

 

Just ordered a compression tester.
First coil I put on it was a STANDARD MOTOR PRODUCTS brand. Then I ordered the MSD brand because the quality of the STANDARD MOTOR PRODUCTS looked iffy. Got the P0302 code with three different Coils now so I doubt that is the issue. Anybody need a slightly used Coil?

 

Did you check your O2 sensors?

 

O2 sensor wouldn't cause a misfire on 1 cylinder.

 

I'm with Mr Bitey on this. The crank and cam sensors are the issue. The cheap aftermarket brands are not recommended.

 

Anyone know where I can find Mopar Sensors?

 

I understand how bad sensors would make the PCM throw a fault code, but would they actually make the engine run bad? It runs really smooth for the first 15-20 minutes after that it kicks and stumbles like it has a bad misfire and throws the P0302 code.

 

I could be wrong, someone may confirm/correct, but I believe NTK has been accepted as a replacement for Mopar.

Amazon.com: NGK/NTK Crankshaft Position Sensor EH0249 (73315) : Automotive

Buy NGK/NTK Crankshaft Position Sensor EH0249 (73315): Crankshaft Position - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

Amazon.com: NGK/NTK Camshaft Position Sensor EC0160 (73735) : Automotive

Buy NGK/NTK Camshaft Position Sensor EC0160 (73735): Camshaft Position - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

I should also go on record: I am NOT saying it is the CRK/CPS. But I do know I have seen folks poke in here near weekly complaining of misfires and rough idles, only to find they used house brand sensors. This could be a PCM thing too, something I am not an expert on. I do find it curious that it is only #2 misfiring. None the less. If it were me pointing the parts cannon with any itchy trigger finger at it, and knew there generic house brand sensors in there, I would replace them. I have not heard of success from Hitachi before, and NEVER heard of Tamkken...

 

Have you checked the wiring from the pcm to that injector? I wonder if something is rubbing once things heat up.

 

+1 on injector wiring. Injector AND coil connectors can go bad. Those are at least free checks before pulling another hondo out of your wallet....

 

If I'm reading this correctly, the problem occurs after the engine has got warmed up after 15-20 minutes. So what changes as the engine warms up? Is it a fueling issue?

I refer to this when looking at fault codes - P0302 Cylinder 2 Misfire Detected - may be worth reading the whole thing, but I usually start with the 'causes' section.

 

Hampshire- great article 👍🏿

 

Thanks to everyone for the input. This weekend I will check for a vacuum leak, test the compression in each cylinder and re-inspect the wiring. Hopefully I'll find something. If not, I'll order the NGK/NTK Sensors.

 

If it is cylinder specific as the 302 suggests I would thin the problem is going to be cylinder specific. I can' think that changing the sensor will right the problem.

I just asked Mr Google this question - cylinder stops working when engine warm - and here's his answer - A cylinder stopping when the engine is hot often points to a failing ignition coil, worn spark plug, or clogged fuel injector, as these components can degrade with heat. Other causes include vacuum leaks from the intake manifold, issues with the engine control sensors, or even mechanical problems like low cylinder compression. Troubleshooting involves swapping coils and spark plugs to isolate the problem or using a diagnostic tool to check for sensor faults and compression.

Can you swap an injector and plugs into another cylinder and see if the problem goes to that cylinder?

Have fun and good luck.

 

I’m with Hampshire on this one(again). Concentrate on number 2.

You will have to work on it hot for compression and spark after it has started doing it’s thing.

If both are good, it’s fuel delivery time.

 

Me too on:

I’m with Hampshire on this one(again). Concentrate on number 2.

If the compression is good all the way around...
...IMO, at least on the 4.0 engine, it's easy enough to pull the fuel rail and swap places of #2 and #3 injectors; reinstall fuel rail and start engine, check for any external fuel leaks from each end of all 6 fuel injectors @ both the fuel rail and intake manifold ends and if any, deal with that first...

...If misfire went to #3 and it's not misfiring on #2 any more, then it is the fuel injector; If #2 still misfires and #3 is still good, it will most likely be electrically related specifically to #2 fuel injector; whereas, I would inspect the 2-pin connector of #2 fuel injector for any damage and also for + battery voltage with ignition key on...
...If it is misfiring on both #2 and #3, (not very likely, but possible), 1- it would very likely be noticeably misfiring @ startup, 2- there is more than one fuel delivery/injector problem...

...When you are finished with inspecting and doing all work on the fuel injector/s, @ 'final re-install', it is advisable to replace all 12 of the O-Rings on the injectors with new ones, IMHO.

 

Can we open a raffle on what is the final problem determination?
Another thing you can with the injector is to ohm it before and after the misfire. One could see the coil breaking down like old fashioned ignition coils…run for 15 and quit. Takes right back off after it cools down.

 

On my 01 WJ, 4.0L- 3 summers ago on a hot August day I had identical symptoms you described except a p1391 and crank no start until 15 min later- approx 151k on the clock. Ordered a NTK CPS from Rock…Viola’

 

I have changed about a half dozen crank sensors in these jeeps, and even good ones are easily mis-gapped.
We’ve also had a pcm that did similar goofy stuff…but it was not consistently the same cylinder…but…if the driver gets fatigued and stops grounding the coil or the injector…until it rests…

Remans….throw all the pieces in a pile…then reassemble…and it’s not just jasper.
Starters, transmission, alternators…everything reman.

 

Re:

I have changed about a half dozen crank sensors in these jeeps, and even good ones are easily mis-gapped.

You have to get the correct gap spacer to install the crankshaft sensor, (it is a one-time use part because it gets destroyed when the flex-plate/flywheel turns, (even a little bit). so it must be correctly installed before the crankshaft gets turned after getting it in the housing.

Just as an FYI, for the 4.0 the spacer that I used that worked on the OEM MOPAR Crankshaft Position Sensor when I reinstalled the 42RE transmission is made by
Walker Products and is Part# 235-1378:
If the 'Manufacturer Link to the Spacer will work it's: TecDoc
Below is from the Walker web page from the link above

Manufacturer Website	https://www.walkerproducts.com/
Item/Article number	235-1378
GTIN/EAN	00724620115219
Article type	Ignition > Hardware, Fasteners and Fittings > Engine Crankshaft Position Sensor Spacer

----------------------------------------------------------------------------------------------------------------------------------
I got mine @ Rock Auto, (Link to it HERE). I got 3 of them and have used 2 already, Transmission in-and-out twice). At least I do have 1 spare in the 'dedicated' WJ parts box.

 

So... I fired it up, ran great, let it run until it started misfiring. Sprayed carb cleaner at all intake manifold connection points. No change, so no vacuum leaks detected. I then shut it off. I removed the Coil Stick and 1 through 4 Spark Plugs. Apparently, the guy who designed the fitting on my compression tester never met the guy who designed the Cylinder Head. Took me a bit to figure that the only way to attach the Compression Tester fitting was to remove the O-Ring Seal. So, by that time the engine had cooled significantly. The first time I checked Cylinder #2 it was at 90 PSI. Cylinders 1, 3 and 4 all read 110 PSI. I rechecked Cylinder #2 and it was up to 100 PSI. I'm thinking that there may be something in the Valve Train.
I'm hesitant to order another Crankshaft Position Sensor, because it always throws P0203. Wouldn't a bad CPS cause a random cylinder misfire code?
Any thoughts?

 

I’m pretty sure usual compression should be 120+ with some variation between cylinders. You mentioned this was a reman’ed engine? If so, how many miles on it?

 

About 8000 miles on the reman. I called the mechanic who installed it. He's looking up the details on who he bought it from.

 

So this is my NIGHTMARE Jasper DISATER experience:
I own a 01 WJ 4.0L(orig owner) meticulously maintained from day one, ie oil changes (full sun) every 3-4k, tranny fluid every 30k blah blah. At 152k developed sudden low block rap. I pulled the pan and piston #1 had both piston skirts snapped off in bottom of pan. I ordered a Jasper(anbout $2800) and sent to a local garage as I was 70 years old and no longer able to swap motors anymore. After initial break oil changed and subsequently changed every 2-3k with Blackstone Lab analyses on EVERY oil change. Within 12k 0/zero oil pressure, high antifreeze level in oil and high lead and copper levels==> new engine shipped with 100% warranty coverage for replacement.
Eng #2- extremely high antifreeze oil levels and external head gasket antifreeze leakage at #’s 1 and 2.
Eng # 3- again full warranty. Engine installed within 2 days, ready to rock and Roll? NOPE!! Misfire #5. Compression and leak down performed. All cylinders 138-140 except #5 which was 70psi. Determined a valve was hung up. After bicker and dicker(and my attorney intervention), new head shipped within 3 days, installed and drove away everything running tip top.
Just go to BBB/Better Business Bureau and put in “Jasper”…NIGHTMARE!!!

 

If not bad seal on spark plug hole with compression tester and/or something else like a blown head gasket etc and you can narrow it down to cam, lifters and valve-train, here are some videos that may help explain some of the why this can and does happen. Spoiler Alert; it is 'mostly' parts related regarding all the video's main topic:

There are many videos on the topic so you or someone else here may have even better info. and/or links to shorter videos with enough info for you...

...Anyway:
Note: all below links are YouTube Videos:

@ Uncle Tony's Garage on YouTube:
Finally! Some Solid Information Regarding The Bad Camshaft Epidemic
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@ Muscle Car Solutions on YouTube:
Why your Flat Tappet Lifters Failed
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@ Muscle Car Solutions on YouTube:
Flat Tappet Cam Failures: The Reason Why They Go Bad & The Solution! Part 1
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@ Muscle Car Solutions on YouTube:
Uncovering the Truth About Camshaft Hardness: Cam Failure Series Part 2
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@ Muscle Car Solutions on YouTube:
Flat Tappets, New Lifters and a New Book : Billy Godbold - Camshaft Engineer Podcast Interview

 

I've had an horrible thought and I hope it is not the problem, as the problem occurs when the engine is warm, could it be a cracked head? Head gets warm, crack opens up, water and or oil get in head and cause misfire. Would go with reduced compression too.

Hopefully not a case of shooting the messenger!!

 

It’s probably not crank or cam sensor.
20 psi variance is too much on a new engine.
valve cover is nearly free to pull.
it’s sounding like its more likely mechanical.