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Old 10-17-2016, 09:38 PM
My Jeep: 2000 4.7L WJ
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2001 grand cherokee misfiring

My niece brought her jeep by and dropped it off saturday for me to check it out. It has 297,000 miles on it so it has seen it's better days but it is a 4.0 and they seem's to outlive almost anything but it was running really rough and erratic. Put the scanner on it and it had several misfire codes in it. P0300, P0301 and P0306. I started checking the injector's to see if they were firing and injector's 1 and 6 were not firing. I got the FSM out and started digging through but really didn't come upon a solution and my scanner has code connect which give's me the most popular fix and one of those was to replace the TPS. I have a 2000 grand with the engine out of it so I swapped out the TPS and cleaned the throttle body and the #1 injector started firing after that but #6 was still dead.

Looking at the back of the engine I found the PCV plastic line from the valve cover to the intake was broke. Spliced that back together and checked out the wiring around the back side of the valve cover and then the #6 injector started firing again as I was checking them often with a mechanic's stethiscope.

With all the injectors firing the engine was running better but still seemed to be misfiring so I decided to check the spark plugs and they were pretty crappy so I stuck in a new set of plugs and put it back together and fired it up and it ran great!!! No skipping or fluttering at all.

I know it needed a set of spark plugs but i'm sure that's not all that was going on with this thing. I was sure the PCM was bad or something but the more I kept tinkering with it the better it finally decided to do.

It usually doesn't work that way, normally the more I keep messing with something the worse it get's!!

I drove it around the block and it actually ran out great, no spitting or sputtering at all. Not really sure what I did that got it running good but she came and got it and said it ran good going home so who know's??

Anybody had something similar like this happen on their WJ??

I feel like it may have some wiring issues around the back of the valve cover and me moving it around got it working again but I looked at the harness good and it didn't look bad at all but time will tell I guess.

It's got an oil pan gasket leaking at the front so she is going to bring it back in a couple of weeks for me to put a pan gasket on it and I will see if it's still running good then!!

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