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Yet another Misfire Thread - a year later and no solution

Wahooooman

NAXJA Forum User
Location
Newengland
Hey All,


Hoping for some expert advice on my headache of a Cherokee. Background is my buddy gave me this Cherokee as it was taking up space in his yard Last year. Its my 3rd Cherokee and I Feel like i need to save them all lol.

Its a 2000 Sport with 200k on it and it had a Jasper Engine put in it at 150k. When i got it it had Multiple Cyl misfire, not knowing much about the 2000 model year i thought it would be a simple fix lol.

I was told by a local mechanic when he looked at it that it needed a Cyl head and trusted his judgment. Well it did not fix the problem.... Below is a list of things that has been done and what comes up when i scan it. Any advice on where else to look would be greatly appreciated !


Rough idle, flashing check engine light if driven at highway speed then coming off exit. I.e Going 60 then letting foot off gas taking an exit.
Multiple Cylinder Misfire
Cylinder 1 misfire
Cylinder 6 misfire

Things Checked and or replaced:
Continuity between PCM and Injectors, Coil Rail for all 3 - All grounds on both injectors and coil
Fuel Leak down - Only looses pressure over 6+ hours - 49 Psi when running
Compression test - all within spec
Cleaned all grounds
Cam Postion sensor Aligned - Once codes were cleared now only showing cyl 6 missfire

Smoke test - no leaks


New Parts (fire the parts cannon)
New Clearwater Head
Remain Injectors
Spark Plugs
CPS (mopar)
TPS (Mopar)
Map ( Mopar)
Intake Temp sensor
Collant temp sensor
Iac
Coil Rail

Also sorry for the super long post ! And thanks in advance
 
What brand of spark plugs? There is the CkPS (flywheel/flexplate) and CPS (cam position sensor). Also, possibly O2 sensor?
 
Wahooooman said:
All grounds on both injectors and coil

The injectors have 12v applied when key on. Ground is pulses to it by the ECU.

I have seen an ECU cause this. A friend's '04 Wrangler did this and I used an oscilloscope to find that the ECU was randomly missing a few injector pulses.

It's likely been giving you cylinders 1 and 6 because they're companion cylinders. Your spark (I believe) is a wasted spark system, so it's probably having a hard time distinguishing which one of the cylinders is misfiring.

Sounds like you've done some good diagnostics though. I'd re-verify the compression check, give the wires a wiggle test, and if that all checks out, find a replacement ECU.
 
- x2 on the compression test Dry then Wet after its well warmed up. leak down test can tell a lot to.
- new sensors dont mean they are good, believe me I went on a long chase with pros confirming a part worked when it didnt......
- If you have a spare PCM it is worth trying out

Now youve said the cam position sensor is aligned, is this an accurately indexed cam with TDC properly adjusted before the install of the cam synchro?

If all this has been double checked with other partsa a multimeter will only tell you so much, min/max could be useful, but really what you need is an oscilloscope so you can see what the PCM, CPS, CKPS are putting out. This can be bought cheaper than a diagnostic from a shop. If you know anyone with a high end scanner like snap on, autel....many have an o scope built in.
 
Are you sure you got the injector wires paired to the right injectors?
 
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