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2000 XJ 4.0 misfire problems

2kXJ4wd

NAXJA Forum User
Location
Louisiana
Hello everyone. This is my first post on the forums but I have certainly been digging through every post related to my problems over the last 2 weeks. After exhausting all of my knowledge I have decided to turn to the vast experience of the XJ community. Here is my problem, I have a 2000 XJ Sport 4.0 4WD Auto, I have a cylinder 2 misfire and other random misfires. I have read the codes and I got p1694 I think it was and also p300 p302 and 1 for each O2 sensor heater circuit. The XJ runs fine if I remove the battery cable for about 10 minutes and put it back on. The problems come back after 1-50 miles of driving. The Jeep idles rough but seems smoother at speed. There are puddles of condensation with a lot of black specs in it under the tailpipe. I have ran seafoam through it, drove at 4k rpms for 30 seconds a few times, checked adjustment of cam sensor, moved injector and replaced number 2 injector, installed heat shield and wrapped fuel rail and all injectors, cleaned throttle body, checked all connectors and applied dielectric, checked and changed all spark plugs. I changed every fluid in the vehicle. When I changed the plugs I noticed the number 2 plug was completely covered in buildup. After I put the new plugs in I checked them 2 days and 100 miles later and number 2 was covered again. The CEL is on and randomly starts blinking while driving. When it starts blinking the Jeep has almost no power and won't go above 3k rpms. This issue happens if it is hot or cold. Any guidance would be much appreciated!
 
Since I saw that all of them had a failure for the exact same thing I figured it was a ground or something because it affected them all.
 
If it shorts the sensor it wont power the pcm up and will say no bus on the odometer. It sounds like you have multiple issues causing the symptoms. Take care of the codes and continue diagnosis from there. A 2000+ 4.0 with bad o2 sensors will run like crap and miss enough to kick a misfire code
 
The jeep starts and drives fine. The odometer works as it should. The only time that the misfire is noticeable is while stopped and idling. I don't want to put in a new sensor and short it out immediately. If it was the 4 O2 sensors wouldn't it affect more than 1 cylinder?
 
The only time that the misfire is noticeable is while stopped and idling.



Because thats what a 2000+ jeep does when it has 1 or more bad o2 sensors. The computer is telling you where to start you should pay more attention to it. You wont short the sensor straight out, if it was killing sensors from the jeep side it would have other major issues

The single cylinder misfire could be a result of a number of things exposed as a result of the running rich with bad o2 sensors. Could be a leaky valve or seal letting oil through.


Fix what you know isnt right first and then evaluate it
 
it took me a long time to figure it out, I put noid light on the injector and started looking at harness wiring , but one day it wouldn't start and it was the crank pos sensor and replaced it with a new one and has ran fine since
 
Thanks for the reply, I have put in a new cam sensor and I have a new crank sensor on the way. Hopefully it works, I have never had a problem starting though.
 
I never had a problem starting either but would drive and it would give all the random mis fire codes 300 301 302 ext... and then go into limp mode.. then one day it wouldn't start.. no fire so replaced cps and haven't had a issue since..
 
That is great info. Thank you all very much. I will post my results when the new crank sensor arrives. After it runs normal I will install my 3" lift and 33" super swampers. Next week the new radiator, water pump and t-stat and hoses go in also. After that I'm doing bumpers, winch, and some music. Can't wait to hit some trails!
 
Pull the coil rail off & look for any tiny cracks / chalky white stuff on or around #2. If present, replace the coil rail. If not... I'd still lean towards coil rail being the most common cause of misfire on COP engines.
 
No chalky stuff anywhere. With the new CPS it idles about the same but it is intermittent. Sometimes I will stop at a light and it will idle fine, the next light it idles like it has a cam. Also it will idle at about 700 then for a half second it will jump up about 50 rpm like I tapped the gas pedal then go back to where it was. I will check codes again tomorrow and report back.
 
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