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2001 Jeep cherokee misfire/runs rough!!!

Lanser1999

NAXJA Forum User
NAXJA Member
Location
Wisconsin
I have been chasing this issue for a few months now and it is becoming very annoying.
To start off with my jeep never starts on first try, probably the check valve not a big deal. However, everytime I cold start my jeep it will run rough/misfire for a while unless I shut it back off and restart it, then it will run fine. When its warm it runs fine but my fuel mileage hasn't been that great. Any help would be appreciated trying to have this resolved before Winterfest.

I also have a intermittent loud tea kettle noise coming from inside my engine bay, cant find it and is driving me up the wall!!


I also have a new coil pack, and new spark plugs.
 
Define and explain "fuel mileage hasn't been that great" ? What brand and type of spark plugs are installed ? A 30-40% drop in gas mpg's should make one suspect O2 sensor issues. Have you tested the O2 sensors and sensor fuses ? Have you had the battery Load tested and cleaned/snugged all the battery and alternator connections ? Rough starts can be a faulty check valve, and/or can be one or more drippy fuel injectors.
 
Roughly 10 mpg, I have 2 new o2 sensors. I have copper spark plugs. I have not lid tested battery but connections are snug and clean.
 
The whistling noise leads me to believe that you have a vacuum leak. Grab a can of carb cleaner (or some brake cleaner) and spray around the intake manifold to locate any vacuum leaks.
 
Checked all the O2 sensor fuses, and inspected the O2 sensor wire plugs and wire harnesses for corrosion and damage ? Any bent or pushed back wire plug pins ?



Roughly 10 mpg, I have 2 new o2 sensors.....

Doesn't the 2001 have 4 O2 sensors ?

Bosch or NTK O2 sensors ? It is well proven that the OBD-II Jeep 4.0L and Bosch O2 sensors do not play well together and that Bosch O2 sensors commonly cause the CEL to illuminate and/or cause drivability issues.
 
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Replaced with Bosch then had to replace with NTK. It has 4 o2 sensors. I’ll have to check the fuses, but CEL is not on. Another thing is when I cold start it and it runs rough if I hold the RPMS around 2k the misfire clears up.
 
Have you ever replaced the injectors?
 
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