• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Another xj missfire thread

Ohsplat

NAXJA Forum User
Location
florida
Idles very rough after using passing gear. If I'm at around 55-60 and floor it the engine idles very rough for about 30 miles.

Its a 2000 xj 4.0 auto.
Replaced:
Idle conrtrol motor
Tps
Can sensor cap
Coil pack
Plugs new champion copper
Replaced all injectors.
Wrapped injectors and fuel rail with heat tape.
New battery
New alternator
Cyl 1 tests 130# which was the lowest but within 20# of all the others.


Engine code one day will read missfire on cyl 1, and sometimes it says random missfire. The only sensors not yet replaced are map and crank.
 
It still does it after I shut it down and restart. There is a slight bounce on the rpm guage but maybe less then 100 rpm. Its weird because sometimes the cel goes out and when it does the jeep has less power. When the check engine light is on it seems to run better but idles worse. The problem happens after a 10-15 second high rpm run and I pulled the plugs once right after it happened and they were ash grey.
 
OK so I just figured something out. When I put it in park it idles 500-600. When in reverse it Rev's up to 1000 then a steady 800. Shift it from reverse to drive and it drops back down to 500. Something is not telling the computer the car is in drive. I'm sure this is s sensor problem.
 
Another weird thing, when the check engine light is on it has like 30% more power then when it is out. Exhaust fumes are deadly. Also when the cel is off when I let off the gas, the engine has like a cruise control on for a fee seconds.
 
when the light is on it might have turned off the injector to cylinder 1. thus not dumping unburnt fuel down the exhaust.

check to make sure that the crank sensor wiring is not melted on the exhaust. but it sounds like its loose or on its way out.

did you swap out the injectors because of the problem or before the problem?

and if you can do a compression test that would help trouble shoot it.
 
Compression was 120-130 on all cylinders. #1 was the lowest at 120.

The crank sensor looks old as hell but I don't see any issue with the harness. Leakdown test also passed on it. If it turned the injector off wouldn't I have less power?
 
try swaping the spark plug with a different cylinder and see if the problem follows. and if you can use a long screwdriver and try and listen to the injector and see if its still firing.
 
120 isn't great compression. Did you also do a wet test?

As far as having more power when the CEL is on, it may be running open loop (richer).

I would do a vacuum check. Look up what to check for. It isn't just a single value but if it is bouncing around. 15 isn't that great either at your altitude. You could have a vacuum leak or clogged CAT.

I would swap the #1 coil pack with another cylinder and see if the problem moves.
 
All injectors are brand new. Used a noid light and all injectors fire. Same issue with old injectors back in. So the injectors are new and ticking. The plugs are new and putting the old ones in did nothing to help. I'm just throwing parts at it now. No idea if maybe the cps is a OEM or mexico made autozone turd. I've had this issue since I had the jeep.
 
I changed the back o2 sensor when I removed the cat, but the front one is pretty rusted and frozen in. I could not break it loose to change it.
 
120 isn't great compression. Did you also do a wet test?

As far as having more power when the CEL is on, it may be running open loop (richer).

I would do a vacuum check. Look up what to check for. It isn't just a single value but if it is bouncing around. 15 isn't that great either at your altitude. You could have a vacuum leak or clogged CAT.

I would swap the #1 coil pack with another cylinder and see if the problem moves.

The cat is gone, I'm at sea level pretty much in Florida. So your thinking its the engine? I thought dry the pressure of 120 was fine. The manual states 120-150 with no more then a 30 difference I believe.
 
Back
Top