96 XJ Help with New Motor and ECU

I have been looking all over the internet trying to figure this out with no luck so I'm posting here in hope some one can make sense of this.

1996 XJ Sport
4.0L
225k
Auto


My original 4.0 motor died about a month ago. We went ahead and swapped a Reman Motor from Jasper Engines into it. All new sensors where put in with it along with new Cap/rotor/plugs/wires. When we went to start the jeep it would start and Die, after that we checked all the sensors again even tho they where new and the checked out good, Also made sure that the flex plate was good prior to even putting the new motor in.

The last thing we thought about was a possibility of the 1996 PCM going bad. This is where this whole issue gets really interesting. We have the 96 XJ that has a new motor and wont run, and we have a 1999 Jeep XJ that runs perfectly fine. The 99 PCM technically should not run the 1996 at all. To make this easier to understand im going to just list what PCMs start and run the 1996 and what PCMs start and run the 1999. ** Note I'm not saying Driving just getting the motor to start and run.**

1996 Jeep XJ "STARTS AND DIES" with the following PCMs
1. Original PCM
2. Brand New PCM

1996 Jeep XJ "STARTS AND RUNS" with the following PCMs
1. 1999 PCM


1999 Jeep XJ "STARTS AND RUNS with the following PCMs
1. 1999 PCM
2. Original 1996 PCM
3. Brand New 1996 PCM


so basically it will start and run with a 99 PCM but neither of the 96 PCMs. Which does not make any sense at all. Could we have an incorrect Crank Position sensor?



Thank you all for any help you could provide.
Mike

I blew my 96 pcm and temporarily ran a 97 pcm. The only issue I had was the Gen light on. I'm thinking about swapping my stroker and goodies into a 4-cyl 99 and looked at the 96&99 wiring diagrams. The Gen circuit did change pins and the 99 has the leak detection pump that the 96 doesn't have.

how is it dieing? is it slowly sputtering or is it just cutting off after you let go of the key?

Basically as soon as you let the key go....after about ten tries you get PO320 (no crank reference signal at pcm) but circuit and sensor test good. The odd part is that the 99 PCM runs it.

maybe a loose connection or bad sensor. check to make sure the wire isnt broken anywhere.

90xj06 said:

maybe a loose connection or bad sensor. check to make sure the wire isnt broken anywhere.

Click to expand...

if it had a bad sensor, loose connection or broken wire.. then the 1999 PCM would not run the engine. That is what is making this really odd. He can clear the PO320 code.. try and start the jeep with the 1996 PCM 10 or so times before the PO320 comes back.. then clear the code again and throw the 1999 xj PCM in and it will fire right up.

might be the wrong sensor and sends out a lower signal voltage?