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Misfire

O

ottexj2000

NAXJA Forum User
Location
Guilford, CT
OK I know this is proably like every other Misfire thread but here goes nothing.

My 2000 XJ has a bad Misfire. And I mean Bad. I have replaced all the plugs proably 5 times between 2008 and now. The XJ will run a little better for maybe 2 weeks max then come back. I just today replace #3 injector and all 6 plugs again. And had the Battery disconnected they whole time to clear the computer. The Jeep ran mint till I was driving home on the highway 30 mins ago and the misfire returned. Yes the CEL has come one everytime. and a few times it has flashed at me. I always immediatley pull over shut it off and wait or disonnect the PCM or battery and the misfire would be gone for a little bit then return.

Please help. I really dont want to go to a Dealer. Thanks
 
And the condition of the plugs tells you, what?
 
They Looked like normal wear actually. Not too rich or lean. Jeeps are so weird I dont get it. I will try to take a pic of them later on to help with diag.
 
No cooling system is fine. I replaced #3 because it had the hot soak issue as well. I had tried the Ign wiring sheild the dealer sells but that didnt help.
 
What codes do you get from the CEL ?

What brand and type of spark plugs are you installing ?

Have you tested or replaced your TPS, CPS, or Coil on Spark Plug Rail ?
 
What about timing the CPS (Cam Position Sensor) with the toothpick method? There have been many write-up on here for that one. If you need more info on that, let us know. Basically, at TDC #1 compression, the hole in the sensor needs to line up as verified with a toothpick.
 
I think you should stop changing the plugs all the time, if they don't show any abnormalities then they are fine. I am probably wrong, but I believe the NGK plugs are recommended for use with the heat soak problem.

Maybe you should try some of this DEI heat wrap from Summit. Comes in different widths from .625" to 1.5", you could cover the entire fuel rail and all of your injectors with it.
 
My Jeep already has the Heat Sheild. I always use dealer plugs which are NGKs. No I have not tested/replaced the Coil Rail, CKP, CMP or TPS. I believe my TPS is fine because I have good throttle response. The codes were P0300, P0303.

Please help me to understand which sensor CMP or CKP would be better to check first?

I work repairing heavy diesels so Gas engines are a bit foregin to me. Thanks again for help.
 
i'm getting the code P0301. CYL 1 Misfire. Replaced all wires, plugs, cap, rotor, cyl 1 fuel injector, cleaned the throttle body, did a compression test... and nothing.

I am stumpped as well.
 
Did that prodeure last night. And I am keeping my fingers crossed. I can feel a difference in how it runs already. I am going to do a few other little things to my jeep. Like change O2 sensors when I do my cat back exhaust.
 
Well CEL light came on last night as i got home at 1am. I went to Autozone to day and the scanned it. I have codes p0301 Cylinder #1 Misfire, and p1694 Fault in Compantion Mode (whatever that means).
 
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