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Unread 11-27-2013, 07:05 AM   #1
sherminator866
Registered User
2006 LJ Wrangler 
 
Join Date: Apr 2010
Location: mass
Posts: 128
another p0300 code

so ive been searching this for a long while now and just cant seem to figure out what is causing this. i would rather not take it to the dealer and most people online say the dealer doesnt really help much either.

so i have a 06 liberty 6spd 4x4. check engine light came on for random misfire blah blah blah. so what i cant seem to understand is what other parts can i look for and test, if possible, that can be causing this? p0142 (o2 bank 1 sensor 1) just came up yesterday, but i get no other codes for single cylinders. i dont see how it could be coils, injectors, or plugs because if this were the case it would throw the cylinder too i would think. ive changed plugs, crank sensor, and fuel pressure was at 60lbs for about 10 mins straight, also swapped the asd relay with blower relay and it didnt help. i know there is a ton of other threads on this, but im not sure what else past what ive done can be checked or looked at by myself.

thanks a ton guys.

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Unread 11-29-2013, 11:25 AM   #2
AVR2
Web Wheeler
1993 ZJ 
 
Join Date: Apr 2007
Location: UK
Posts: 2,221
This won't help you, but FWIW - on my 2005 KJ, I occasionally get a CEL for a random misfire (say, every 500-600 miles or so) that sometimes goes on to be pinned down to cylinder 1 or cylinder 2. If I do nothing, the CEL goes off after the set number of key cycles (I think it's 40), meaning that the problem hasn't recurred - until about 600 miles' time.

I changed all the coils and plugs back at the start of the year, so I don't think it's those. The crank sensor is still the factory original at 125K miles.

I did find the diagnostic manual (note, NOT the FSM - the diagnostic manual is separate) for the KJ online somewhere, which laid out the full factory procedure for chasing down misfires. I think I'll have to try and find it again. It was quite involved and needs the DRB3 to complete in full, but essentially it tests every possible cause, including a leaking fuel injector.
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Unread 11-29-2013, 07:39 PM   #3
flexyxj
Registered User
2009 XK Commander 
 
Join Date: May 2005
Location: Sioux Falls,SD
Posts: 491
Quote:
Originally Posted by sherminator866 View Post
so ive been searching this for a long while now and just cant seem to figure out what is causing this. i would rather not take it to the dealer and most people online say the dealer doesnt really help much either.

so i have a 06 liberty 6spd 4x4. check engine light came on for random misfire blah blah blah. so what i cant seem to understand is what other parts can i look for and test, if possible, that can be causing this? p0142 (o2 bank 1 sensor 1) just came up yesterday, but i get no other codes for single cylinders. i dont see how it could be coils, injectors, or plugs because if this were the case it would throw the cylinder too i would think. ive changed plugs, crank sensor, and fuel pressure was at 60lbs for about 10 mins straight, also swapped the asd relay with blower relay and it didnt help. i know there is a ton of other threads on this, but im not sure what else past what ive done can be checked or looked at by myself.

thanks a ton guys.
We had a similar situation with our '02 KJ. Change the o2 sensor and clear your codes. I chased a random misfire with an occasional o2 sensor code and thought the misfire code was causing the o2 code but it was the other way around. The o2 code was causing the misfire codes.
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