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-   -   PCM failure? (https://www.jeepforum.com/forum/f11/pcm-failure-3919650/)

Bradahman 11-07-2016 06:30 PM

PCM failure?
 
I got a decent (134K miles) 1998 Limited with 4.5" lift w/ 33's, lockers, fenders cut out and plenty of evidence it has been off-roaded regularly in barter. Owner told me all I needed to do was fix the broken frame and I could drive it home. The rig is an hour away from home and with little time to spare took me a few weekends to completely box in the frame. When it gets home I will fab the brace.


Welding done, only two fires in the grasslands from welding and grinding... I do a complete electrical tuneup thinking I can drive it home. No go. Fuel pressure but no spark. Owner tells me then that they had driven it to where it was parked but that it was having an issue of popping a relay (three were laying on the floor, 2 tested good later). I leave and grab a few for the next visit.


I went back this last Saturday and find these: no fuse in pcm slot interior fuse block (I put a new 20amp in), I swapped all 7 (I think) relays for ones that tested good, the input wires for the coil were bare for 1/4" at the plug and twisted into one wire (I separated and cleaned them), CPS tested good. After all that still no spark. I have to admit I screwed up the test on the inputs so my deduction that there is no 12v is suspect. Pulled the coil and got 2.4ohms at the primaries and 12.2 ohms at the secondary, out of spec from the info I got here and indicates a weak, on the way out coil?


I looked up repair on the PCM and got exited by all the posts on fixing them, Grand Cherokees that is... I can't figure out how to open the PCM with the three sided single panel. Can it be worked on?


My main question is can those bridged wires from the input cause backfeeds to the pcm that would have allowed to drive for a time, very badly, and then ultimately not send the signals to the coil? I didn't bother with the cam sensor or O2 sensor as there was no 12v at the inputs (recall my test was flawed).


Thanks in advance, and I tried to be as comprehensive and succinct as possible.


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