1999 XJ Computer Swap

So the history of this is my buddy's 1999 XJ was having issues with starting up, running for only a few seconds then shutting off. We went through every sensor we could think of, tested all electricals and had it scanned with an ODBII scanner. No codes. After re-cabling the battery, thinking it might be a ground issue, the truck ran a bit better but would experience the issue once it had run for more than 10 minutes and was then attempted to be restarted.

This would lead to the situation again where the XJ would start, then shut off after about 3 seconds. It turned out the ECU or PCM or whatever its supposed to be called was extremely hot after a shutdown. Cooling it off would allow the vehicle to be restarted without issue. So the plan was to replace the computer with a matched unit from another XJ. The original was an 56041-493AD so we found a 56041-493AE, understanding this was essentially the same computer with a newer firmware we felt confident it would just swap in. The donor was a 99 XJ with matching specs (4.0, auto etc) but following the swap the XJ wouldn't run for more than 3 seconds with the new PCM.

So the end result is we had to put back in the other PCM, which would allow it to at least run. Is there any other reset process, or re-programming needed to address using a new PCM? Any ideas or paths we should pursue? We're replaced the TPS, CPS and MAP sensor and everything else we could think might be causing this issue. Thanks for any input or ideas,

Tim 'Skorpyo' Kilpatrick

Does the buddy's XJ have the factory installed SKIM anti-theft system ? Simply look at the ignition key, light gray plastic and thicker profile are SKIM, black plastic or plain metal keys are not.

Running for 3 seconds, and then shutting off, is the what the SKIM does to prevent theft. Even when the system has failed it does the same thing.

Tim_MN: thanks for the reply. I followed your info and researched it further and now understand the SKIM and key issues with a ECU swap as you described. Thanks for the info. I found a local jeep dealer who said they could reprogram the new ECU for a reasonable price (compared to online ECU resellers). I'll let you all know how it works out. Thanks again,

Tim 'Skorpyo' Kilpatrick

Take a look at my thread. I highly recommend the place I went with for the PCM.

http://www.naxja.org/forum/showthread.php?t=1106580

Depending on the budget for repairs, I would remove the SKIM module and install a non SKIM enabled PCM from the junkyard. If the PCM part numbers are similar, and the donor had the same engine/transmission, reprogramming the PCM is not required.

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If replacing the PCM with a non SKIM unit. MAKE SURE the SKIM is out of the vehicle prior to powering up the replacement PCM. Once it sees the SKIM, it will have to have it or the PCM shuts down. Another anti-theft feature. This was done, as I understand ti, so that the thief could not just remove the module and drive away happy.

Also, be advised that there are multiple PCMs of every year:
1) Manual Transmission, California emissions.
2) Manual Transmission, 49 State emissions.
3) Manual Transmission, Export.
4) Automatic Transmission, California emissions.
5) Automatic Transmission, 49 State emissions.
6) Automatic Transmission, Export.

All of these will accept the SKIM module as an installed component.

Thanks for the info guys. My buddy, after talking to the dealership, decided to order a replacement online. Should be here in a few days. He ordered before he asked me or I would have recommended your place cause it's $40 cheaper than he paid. Oh well. He's not an internet guy so he didn't read this. Thanks!

I sold the "new" computer to Skorpyp and am trying to get him the SKIM thingy .... but I don't think the donar Jeep has one (at least not the one in the picture above).

Also, the donar Jeep just uses a plain old metal key .... does that mean it doesn't have the SKIM box?

MrSimon, I appreciate it, but you can stand-down. The PCM may not have had the sentry security enabled, but once it was put on the XJ with the SKIM it would have seen the SKIM, enabled security, and then failed to start due to the VIN mismatch. At this point the new PCM coming in the mail will have the VIN programmed in and will match-up allowing it to run the truck. I never knew Jeep put a decent security system in these XJs. Thanks for the info and support guys,

Tim 'Skorpyo' Kilpatrick