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Misfire help needed

socalrex1

NAXJA Forum User
I have a 2001 Cherokee sport with the 4.0 4x4 and it has a random misfire causing it to run like absolute shit.
Process of elimination has begun and I have no clue what it could be at this point. So to start I’ll list everything I have tried and see if anyone has suggestions

1. Compression tested all between145-155
2. Fuel pressure checked consistent at 50-55 driving or idling
3. New plugs
4. New coil pack
5. New crank sensor
6. New cam sensor and synchronizer
7. New map sensor
8. New pcm ( flashed correctly)
9. New engine harness(replaced yesterday off same exact vehicle)
10. New o2 sensors (all4)

I have been trying to figure this out for quite some time and am getting to my wits end any advice would be greatly appreciated
 
Are all the new engine sensors genuine Jeep parts ?

Read this >> http://jeep.blackonyx.net/pdfs/jcss.pdf , and then grab a toothpick. If necessary, print it out and find a shop that understands the info and has a DRB-III scan tool and oscilloscope.
 
First run a can of BG44 through the gas. It will clean the injectors and carbon out.

I run a can every 10k miles in everything I own.
 
subbed, I have a similar prob thought it was heat soak, got the insulators from Jeep. was ok. Now its warm again its doing it again. Checked all the above, did seafoam, moved injectors. The injector code always sets before the misfire. Wiring all checks out ok. Starting to suspect PCM.
 
PCM failure is highly unlikely and only should be considered after a complete and thorough diagnostic of the more common and likely causes of misfires.
 
That's what happened to my 2k, bad wire shorted out my PCM output on #6!
 
Are all the new engine sensors genuine Jeep parts ?

Read this >> http://jeep.blackonyx.net/pdfs/jcss.pdf , and then grab a toothpick. If necessary, print it out and find a shop that understands the info and has a DRB-III scan tool and oscilloscope.


I have already tried the toothpick and ended up just replacing the whole synchronizer after that didn’t fix it. I unfortunately don’t have the means to get it into a shop for them to scan it.
 
socalrex1, did you figure out your misfire? I've done everything you have and more on my 2001 and I am still getting misfires and running crappy..
 
socalrex1, did you figure out your misfire? I've done everything you have and more on my 2001 and I am still getting misfires and running crappy..

Are you sure the cam synchronizer is correctly set? Being slightly out of adjustment will cause misfires and drivability problems.
If you have the stock synchronizer, its pulse ring is drilled and you can use the 'toothpick' method, as shown in the FSM.
If you have an aftermarket synchronizer, they are not drilled and usually come with a plastic adjustment guide. I carry one in the 01's tool bag.
 
Folks, I have the answer to this question. I know it has ran us all in circles, but last night, we figured it out and the answer is so simple and cheap you’re going to kick yourself. The 4.0 gets a few miles on it and the timing chain gets some slack, if you will use a small Allen wrench or toothpick to set your timing at the distributor (cam sensor) the problem goes away. I kid you not. The scanners very rarely pick up on code P1301 cam/crank sensors out of sync. It will cause intermittent stumbling, stalling, misfires, and the only code it will set is intermittent misfire on one or two cylinders. I could go into the process of finding the issue, but I won’t. Just know that all the money you spent on sensors, was not necessary. Yeah this was a problem for 18 months on a customers Jeep before they brought it to us. Set your timing, adjust your crank sensor gap and let it ride.
 
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