PCM from working Jeep not working in other Jeep

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OlTrustyYJ

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Pennsylvania
Hello:

I have 2 1995 YJ 2.5 with 5 speed manual transmissions (and a 95 yj 2.5 with an automatic transmission).

My daily driver started intermittently chugging and few months ago. After all the normal replacements of Cap, rotor, fuel pump, etc, I narrowed it down to the PCM. My parts jeep, which now looks picked over like the thanksgiving turkey by Sunday, has been sitting for 4 years. last started 3 years ago. I took the PCM off it and on the daily driver and no start. Put the original back in and fired up. Same 828 part number.

Anyone have an idea why it wouldn't start with the spare PCM?

Pulled the cover off the spare and saw some cracks in the goo. other than that, all the capacitors are good.

Only thing I can think of is that the daily driver is a rio grande and the parts jeep is a regular wrangler, but the part is the same number.
 
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If they're the exact same part number, then they are the same part. There is no programming, all the different PCMs in the YJs are differentiated by part number only, so similar and same part numbers are the same. Sounds like the spare went bad while sitting, and bad in a different way than the original. If I read your post right, you have three 2.5 YJs? If so, grab the one out of the automatic and see if it works. I read it as you have 2 manuals and an automatic.
 
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As macho said, that one PCM is probably bad. I would do like he said and swap the auto pcm in. If it runs on that one, than that pretty much narrows down your issue.

When you swapped in the parts PCM, did the check engine light come on when you turn the key?
 
Thought about pulling from the auto; however, auto's get a different programming (if I understand it correctly). That jeeps runs flawlessly (just made a 1500 mile trip and back with no problems), so I'm a little leary about touching it. I'm assuming that you are all correct that the part went bad. It's been outside and a good chunk of the time the hood was open. When I pulled the PCM apart, I did see that there are many cracks in the resin. Could have gotten water damage.

Thanks for your thoughts.
 
Not in a YJ. Same programming. Other than things like the shift light or torque converter lockup. But either pcm will run either transmission fine, except a manual PCM will not lock up an auto torque converter on a 94-95. It would be a totally valid way to test and prove a pcm bad at the bare minimum.
 
machoheadgames said:
Not in a YJ. Same programming. Other than things like the shift light or torque converter lockup. But either pcm will run either transmission fine, except a manual PCM will not lock up an auto torque converter on a 94-95. It would be a totally valid way to test and prove a pcm bad at the bare minimum.
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Interesting. When I looked online for PCMs, the listings said they must be factory programmed for automatics.
Worth a try though.
 
OlTrustyYJ said:
Interesting. When I looked online for PCMs, the listings said they must be factory programmed for automatics.
Worth a try though.
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It’s a CYA thing, lots of people have swapped them back and forth. The only thing I wouldn’t do would be to run the manual PCM on a 94-95 auto long term because the TCC could technically overheat if it isn’t locked. Though that can be wired up to be operated manually in a pinch. But anyways it will work fine for testing, I’d give it a shot.
 
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