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2000 Cherokee XJ Misfire Mystery

Ima Doit

NAXJA Forum User
Location
Atlanta
I’m trying to fix my son’s jeep. Giving me a tough time. This forum was super helpful with my XJ years ago. Now I have another and it’s a project.

Drove good for 6 months. Now, it’s throwing the following codes:

P0351
P0300
P0301
P0306

I know cylinder 1 and 6 share the same pulse. Replaced the coil pack and spark plugs with NGK. No change.

Potentially unrelated. He was having heat soak issue. Restart when hot was causing cylinder 3 misfire. Sluggish start then cleared up.

I verified continuity between pin 7 at the PCM and the connector to the coil pack. Wires don’t appear to be issue. Even jiggled around and kept continuity.

Fuel pressure around 50psi.

Took coil pack off again and checked for spark. Had spark on 1 and 6. Used test light.

Compression test between 165 and 172 on each cylinder. No coolant in oil and coolant still looks good. Popped off valve cover to replace gasket and didn’t see anything of note.

I’m stumped. Any ideas?

When I cleared codes after putting everting back together, it ran well for a couple miles or so until I gave it the beans. Didn’t like that. Started misfiring again. Same codes.
 
Electrical insulation breakdown is a very common issue! It can also cause a failure of the PCM drivers.
 
I actually bought a PCM for it. Same model number. Starts the jeep then dies within a second. I guess maybe it needs to be flashed. No idea how much that might cost.
 
I definately wouldn't install it until I knew the wiring is good!
 
It's insulation breakdown that's the issue , the wires short out to a ground source.
 
You really need a megger to test. I tried a few years ago to find the right pin connector but I never did!
 
We have been battling the same kind of issues. Same codes except we did not have the P0351 code. I even swapped the ECM from another 2000 Jeep which you cannot do without having it programmed to work with your key. Ours would start and cut off almost immediately. Our issue ended up being an O2 sensor that had a broken wire. We replaced all of the O2 sensors, about $130 bucks from Rock Auto and it runs like a champ now. Premature excitement. It ran great for 50 miles and now is back to running like crap once it gets up to operating temp. Same three codes showed up again, but the running rough part clears if you shut the Jeep off and turn it back on again, until you slow down around a corner or stop at an intersection. Back to the drawing board.
 
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I am going through this too. I did have my EMC tested. I sent mine to ECM Repair1 in Tilden IL. They didn't find an issue with it. Bench fee was $96 or so. The EMC was cleaned. Good luck.
 
Did you check corrosion in the plug ends? Also, my son's 01 long coil pack 'bar' had little tiny cracks and was 'bleeding' spark through there.
Just for kicks, check for spark bleeding in a dark garage or night.
And check the asd relay. I had an issue where it started then before let go of the key, it dies..
 
1997-2001 a replacement/junkyard ECM/PCM with the same Part Number can be installed without flash memory re-programming with two related EXCEPTIONS. 1) If the XJ in question has the factory installed SKIS/SKIM anti-theft option, remove the Chip-in-Key reader device before installing the donor ECM/PCM. 2) If the Donor Cherokee PCM has the factory installed SKIS/SKIM anti-theft option The ECM/PCM will require flash memory re-programming, or you need the Chip-in-Key reader device that is married to the ECM/PCM from the same donor Cherokee.



Possible Causes of the DTC P0351 Jeep?
  • Faulty Ignition Coil 1
  • Ignition Coil 1 wire harness is open or shorted
  • Ignition Coil 1 wire plugs poor electrical connection
  • Faulty Engine Control Module (ECM)

Visually examine the corresponding wiring harness and wire connectors. Ensure to check for any damaged components and inspect the wire plug connector pins for signs of broken, bent, pushed out, or corroded wire plug pins. Inspect individual wire for deteriorated wire insulation, especially at the wire plugs.

When is the Code Detected? Each ignition circuit is continuously monitored by the Engine Control Module (ECM). The test fails when the ECM does not receive a valid pulse signal from the ignition coil.
 
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Appreciate everyone’s input. To not leave everyone hanging in suspense and in case this helps anyone in the future, I got it repaired. I doubted it was the PCM. So, decided it had to be in the wiring between the PCM and injector rail. I decided to try the plug first. Bought a new one with 6” of wire. Then cut off the existing plug and about 2” of wire. Spliced the new in. Cleared codes and fired it up.

She’s been back on the road about 15 miles and no issues. If there was any corrosion, it’s gone now.
 
Nicely done fixing it. Double points for coming back to close out your thread!!
 
Bought a new one with 6” of wire. Then cut off the existing plug and about 2” of wire. Spliced the new in.
I tend to avoid pigtails as much as possible. But in this case, it's the only way to go. Chrysler could have just added one more inch of wire, cheap bastards. That damn plug is a pain in the ass. Your solution with the extra wire is a definite game changer.
I'm having similar issues. Your method looks to kill two birds with one stone. Thanks for posting up!
 
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