XJ charging issue and PCM replacement compatibility

I have a 98 4.0 AW4 that was having a charging issue. Replaced Alternator, no change (it did bench test as bad)., Then replaced all power cables with new ones from Kelly WIP (old ones had some corrosion, so thought they might be causing problems). I was still was not getting a charge, only 11.7 volts when running according to a voltmeter. Read something that said next would be to try a different PCM. Checked a few local pick and pulls and could not find a 98 4.0 AW4 that still had a PCM in it. I did find a 99 4.0 AW4, so grabbed that PCM to try it out. With the 99 PCM the XJ charges fine, so I was able to confirm that the 98 PCM was bad.

I read that the 99 PCM uses a different oil pressure sender, so my oil pressure idiot light did turn on. I have the cheap style cluster with only idiot guages. Is there any other issues i need to worry about if running a 99 PCM? and can i simply install a oil pressure sender for a 99 and be all good to go? Or do i really need to keep looking and use a 98 PCM?

Another unrelated question, the 99 had a full cluster instead of just the idiot lights, if i go back there, would the cluster from a 99 work in a 98?

dysfunctionaljd said:

I have a 98 4.0 AW4 that was having a charging issue. Replaced Alternator, no change (it did bench test as bad)., Then replaced all power cables with new ones from Kelly WIP (old ones had some corrosion, so thought they might be causing problems). I was still was not getting a charge, only 11.7 volts when running according to a voltmeter. Read something that said next would be to try a different PCM. Checked a few local pick and pulls and could not find a 98 4.0 AW4 that still had a PCM in it. I did find a 99 4.0 AW4, so grabbed that PCM to try it out. With the 99 PCM the XJ charges fine, so I was able to confirm that the 98 PCM was bad.

Click to expand...

Sounds like a bad PCM

dysfunctionaljd said:

I read that the 99 PCM uses a different oil pressure sender, so my oil pressure idiot light did turn on. I have the cheap style cluster with only idiot guages. Is there any other issues i need to worry about if running a 99 PCM? and can i simply install a oil pressure sender for a 99 and be all good to go? Or do i really need to keep looking and use a 98 PCM?

Click to expand...

The 98 harness only has 2 pins for the oil pressure sensor and the 99 uses 3 pins.

dysfunctionaljd said:

Another unrelated question, the 99 had a full cluster instead of just the idiot lights, if i go back there, would the cluster from a 99 work in a 98?

Click to expand...

Yes, it will work on your 98.

OK, so i have to get a 98 PCM, because the oil sensors will not simply swap out, as the plugs are different. Guess i'll take back the 99 PCM, and grab that 99 instrument cluster instead.