Misfire/Shifting Issue - HELP - Jeep Wrangler Forum

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Old 12-01-2012, 01:25 PM
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Misfire/Shifting Issue - HELP

2002 TJ 4.0L 32RH Automatic Transmission 142k Miles

Since mid summer my jeep has been acting up on, I believe it may be the Fuel Pump/Regulator going. When I go to start it up in the morning, it would stumble at first and then eventually fix itself and run fine. After I would run it for a bit and let the engine get up to temp, if I turned it off and went to go restart it, it would stumble again for a few moments.

Also, I noticed that when taking long trips at high speeds, the check engine light would come on for P0300 Random Misfire, sometimes it would be a code for a single cylinder and other times it would be multiple which is telling me it cant be a single bad fuel injector if its always different.

Just yesterday, I took a long trip to MSU, roughly 90 miles from my house, and it got there with no problems. As soon as I got there I went to run out somewhere and it stumbled a bit, finally fixing itself. When I started going the engine light turned on, from what it seemed, it would nt shift into 3rd gear. I would press all the way down on the gas and it would just rev rpms but would not shift over into 3rd. It had trouble even going 35mph.

I am obviously really hopeing the trans is not the issue, but when I checked the code once again it was random misfire and nothing trans related...

Things Ive done:
Cleaned the throttle body and IAC Sensor
Checked the resistance of the Coils (while it was cold) came out fine
Changed the spark plugs (OE Champion)

Lastly I did a fuel pressure test, when I would turn the key to the ON position before starting it, the gauge read 20 psi...obviously there is an issue with the fuel system.

The obvious answer would be to just put in a whole new fuel pump but my question is, could a pump/regulator get so bad that it wont give enough power to let you shift? I am wondering if this is a transmission issue, or if it just wasnt getting enough power to go over into 3rd, even though the pedal was to the floor and rpms were high.

Note: Ive never encountered any problems with the trans before, just changed the fluid about 3 months ago and has been fine.

Any information would be greatly appreciated!!!
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