I've tried just about everything I can think. Cleaned grounds. Made sure they're all good. O'Reilly tested and said I have a failed voltage regulator. I checked the voltage of the battery and the alternator. Both are 10-11 with the engine on and off. Is it more likely it's a bad alternator or is the alternator not getting the correct voltage due to a failed voltage regulator? I replaced the PCM 80k ago when I got it due to a misfiring problem. I don't want to spend the money on that if I don't have to. I have a new alternator, it's just a pain to get out to have it tested. But I suppose that's my next logical step

 

There is a fusible link from the alternator to the PDC that can be fried. There is a 2-pin connector on the back that the PCM uses to drive the field coil and energize the alternator. You should see some voltage across there if the PCM is commanding the alternator to charge. (dark-green/orange and dark-green wires if my FSM is correct).

 

I jostled some wires around, tightened the grounds, the battery leads and tightened my belt and it seems to be functioning again. I'm at 161k, should I replace the alternator now or wait until it goes out?

 

Update:
put in a reman alternator. The old one is probably the original. At times it wasn't charging the battery at all and it was sitting around 10V, and then other times it seemed normal, but slightly low around 12.5ish, the new alternator started charging at 13.5-14 immediately. Got it warmed up and restarted it a bunch since that's when the problem was most likely to occur. Haven't been able to replicate the issue with the new alternator. Will drive it through the week and hope it was the issue. The old alternator looks like crap, can hear the brushes on the inside moving and spins very freely. The new one is harder to turn and silent. Will keep the post updated if anything changes.

 

This also highlights why you take Oreilly's test with a grain of salt. I'm guessing the counter jockey hooked up the tester and repeated the first possible cause of no charging shown on the display, without doing any troubleshooting that would have confirmed it was the alternator. Testing that anyone with a voltmeter and a little knowledge can do.

Oreilly, Schmucks, and Autozone around here generally give poor advice (with the exception of that teenage girl with the lifted XJ at Schucks who knew the older Cherokees inside and out!). My local NAPA counter guys/girls and the machine shop guy are awesome.

 

Final update, hopefully.

Had the old alternator tested, failed miserably. New alternator has be back up to normal charge. A bit worried that my battery may have suffered, but bottom line, don't listen to O'Reilly's diagnostics. Had me so worried that I had to replace my PCM.
Should be good to go now

 

Did you replace the PCM?