Do PCMs need to be flashed? '95 ZJ

[fattmann]

Buddy picked up a '95 ZJ with the 4.0l in it, and the dealer is telling him it needs a new PCM. It will start, runs like crap for a little bit, like its waaay out of timing, then sometimes die. He took the PCM into the dealer and they said it was bad.

Now, they are saying he'll need a new one (~$350), and they will have to flash it (~$100), but he has to have the vehicle there for them to do it (+$$ for tow).

We've read a few posts saying that you can just plug and play PCM from a vehicle with the same options, and some posts saying you have to get it flashed. On top of that i don't see why you would need the vehicle there, there are performance websites that you can ship your PCM to and have it flashed, car unseen.

We know little to nothing about PCMs in general, and are getting everything from hear-say. Haven't had a chance to check continuity on the whole harness and what not. The PO had replaced just about every sensor in the engine bay before he picked it, but you never know.

Any suggestions are greatly appreciated. I know it's not an XJ, but you guys know the 4.0l so thought this would be a good place to start.

 

[McQue]

by no means do I think I know as much as any Dealership mechanic, but it doesn't sound like you have a bad PCM to me...PCM's can be flashed offsite, that dealership may not be set up to do it that way though. Another junkyard PCM from a similar configuration can be swapped in. Have you checked timing? Many threads here on how to do it.

 

[fattmann]

He claims he did the timing the other day, but i was not present. What Would the symptoms of a bad PCM be (while i'm sure there's many..)? We swapped in one from a '95 XJ that a buddy had laying around, had almost the exact mechanical response, although slightly worse. It was at that point i told him to try everything he could before dropping that much cash at the dealer, as it sounded a bit fishy..

Read a thread on earlier where someone turned out to have a bad factory splice in the loom, told him we needed to check all continuity and ohm-age for the loom.

Mainly just wanted to confirm that they could be direct swapped. I think the dealer is trying to take him for his money..

 

[McQue]

PCM's get replaced for lots of different failure symptons: injector firing circuit(s) dead, ignition/spark circuit dead, 5 volt supply dead, etc. etc. If you swapped in another PCM and the performance only changed slightly, I seriously doubt that you have a bad PCM.

 

[JJacobs]

Proper diagnosis should find the problem. Beware of just hucking parts at it to see what sticks.

 

[winterbeater]

I think the newer ones have to be flashed to read the chip in the key, but your's should preceed that IIRC.

 

[kastein]

Legally speaking I believe they need to be flashed to update the mileage and VIN, but to get the engine running I think as long as it's from the same model year / engine / transmission combo (maybe) it should work.