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  #1  
Old December 4th, 2016, 18:15
Ohsplat Ohsplat is offline
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Another xj missfire thread

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.
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  #2  
Old December 4th, 2016, 18:20
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sinat01 sinat01 is offline
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Re: Another xj missfire thread

Possible vacuum leak somewhere? may sound silly, but it is a jeep...
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  #3  
Old December 4th, 2016, 18:34
Ohsplat Ohsplat is offline
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Re: Another xj missfire thread

If I remember right, the vacuum was -15 at idle
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  #4  
Old December 4th, 2016, 18:47
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Re: Another xj missfire thread

Starting to wander if the intake is cracked
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  #5  
Old December 5th, 2016, 07:14
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90xj06 90xj06 is offline
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Re: Another xj missfire thread

if you shut it down and restart it does it still do it? is your rpms dropping out to 0 and bouncing back up?
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  #6  
Old December 5th, 2016, 07:19
Ohsplat Ohsplat is offline
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Re: Another xj missfire thread

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.
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  #7  
Old December 5th, 2016, 07:20
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Re: Another xj missfire thread

Would the map sensor throw a code? I'm thinking it could be bad
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  #8  
Old December 5th, 2016, 07:23
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Re: Another xj missfire thread

do you know what code it is? sounds like it might be a loose crank sensor.
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  #9  
Old December 5th, 2016, 09:01
Ohsplat Ohsplat is offline
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Re: Another xj missfire thread

P0300 P0301
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  #10  
Old December 5th, 2016, 09:39
Ohsplat Ohsplat is offline
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Re: Another xj missfire thread

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.
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  #11  
Old December 5th, 2016, 10:44
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Re: Another xj missfire thread

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.
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  #12  
Old December 5th, 2016, 10:49
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Re: Another xj missfire thread

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.
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  #13  
Old December 5th, 2016, 11:27
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Re: Another xj missfire thread

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?
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  #14  
Old December 5th, 2016, 12:28
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Re: Another xj missfire thread

Fuel pressure is about 46-47 at idle
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  #15  
Old December 5th, 2016, 13:29
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Re: Another xj missfire thread

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.
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