Need some serious help with charging system!! Something makes no sense!
 

I have a 93 ZJ that I just REFUSE to give up on! I've put a lot into it over the years, but one problem I've never been able to fix is this weird problem its always had with its charging system. I'm constantly frying batteries and alternators! I used to get a couple years before one or the other needed to get changed. Now it seems like, 3 months later, both battery and alternator are shot! This problem is causing the ECU to cook as well.

And here's the thing... The volt gauge in the dash always reported way lower then what the battery and alt were actually putting out. With brand new battery and alternator I've tested them myself and even had it tested by a mechanic. With the gauge in the dash reading 11ish volts, sometimes down to 9, while the motor was running. I would also test with a multimeter at the battery AND the alternator and get the usual... 13.5-14.4 that its supposed to be.

I just figured that the gauge was faulty, so I ignored it! Head lights didn't seem dim, everything electrical seemed to be working perfectly... and with a secondary gauge everything looked fine! But something I just learned the other day made me think the problem is elsewhere... The problem has to be between the charging system and the computer. I never new till yesterday that the ECU acts as the voltage regulator. So shouldn't that mean if the ECU is getting funky voltage it would make the alternator act crazy, which would cook the battery, and then ultimately toast both the alternator and the ECU?

WHAT THE HECK ELSE DO I TEST?!?! I mean... could there be a short someplace in the fuse box under the hood going to the ECU? I don't see how! Anyone have any ideas?

Just figured I would add this in... Battery terminal connections are all new, wires between alternator and battery have been changed to 4gauge wire. Grounds are perfect, even added an extra ground cable from battery to frame just for extra measure!

It could be in the black moulded plastic connector at the back of the alternator, those terminals are for the field circuit and there could be something going on in that black moulded thing. Is the check engine light on?

Nope, no check engine light. I've thought about it maybe being the "black molded thing" as well, never changed it tho. I just suspected it to be a relay that was controlled to act as a regulator. And since checking the voltage with the multimeter and never seeing it spike or dip, I assumed whatever its job is that it was doing it properly.

So theres no voltage regulator aside from the ECU? Cause i have a 93 ZJ and i could have sworn there was a VR on there.

Not that I know of. But like I said, I only heard of this yesterday so I could be wrong. From what I'm gathering out of the information I've heard over the past few days... it sounds like the "black thing" is a relay controlled by the ECU to regulate the voltage. I always thought regulators were built into the alternators.

some are built in, some bolt onto the car or the alternator back side, some are ecu controlled, etc etc

edit: seems its built into the PCM not the ECU

edit 2: aren't there alternator related fuses in the PDC by the battery?

The voltage regulator is in fact controlled by the PCM, SBEC, ECU, PCU, or computer as some call it.

I'm wondering if this is a possibility... The 93 ZJ I have now is actually my second one. It's had the same voltage problem since I got it. Coincidentally the 93 ZJ I had before this one had the exact same problem. The first one got wrecked in an accident so I stripped out just about everything there was to take from it which is why I got the second ZJ....

Anyhow, Now knowing that the comp controls the regulator and both Jeeps had the same problem and I had replaced the comp with the one from the first one and saw no difference... could a new computer potentially solve this problem? I have no choice but to change the comp anyway since both have fried... I just really don't feel like replacing it and frying another one!