I've got a good one. 1996 cherokee 4.0. The generator light came on some time back. I replaced the alternator, put a whole new set of battery cables in, installed an external voltage regulator, and even replaced the PCM. Still have the exact same issues: engine won't stay running, Gen light is on, 20v-40v coming directly off the alternator. Anybody got any idea why it's charging so high?

 

The engine shuts off per design to protect everything from the high voltage. If everything is new and installed correctly, all I can think of is a bad wire or connection somewhere. More specifically a wire with high resistance, meaning its broken, not connected, highly corroded, or any other kind of damage. If its got high resistance, meaning it doesn't let electricity flow easily, it can probably give false readings to the regulator and in turn it freaks out and starts sending out more voltage so it can try to overcome that "resistance". Which in turn shuts the engine off as it should. Check all connections for cleanliness and good ground connections to the frame. The grounds on these jeeps are a big topic when it comes to electrical problems. Matter of fact, just last night my passenger side headlight went super dim for no reason. I took off the ground wire from the frame, sanded it, sanded the spot on the frame, reinstalled with fresh clean surfaces and the light came right back to full brightness. The bolt wasnt loose, no bad wires, just a ground that decided to not work anymore. A little cleaning fixed it right up.

Or maybe you are one of the lucky ones that got a bad regulator from the parts store.

 

Thanks for the advice! I've already checked into some. Like I said new cables, as well as cleaning the harness grounds by the dipstick tube and pcm mounting location. Any other grounds you can think of? Could the alternator itself not be grounded to the block well enough?

 

If you're actually getting 20-40 volts DC off the alternator, then I'm skeptical its connected to the battery. Fusible link or alternator fuse blown? Could also the ground side of the field coil is shorted to the case or your wiring is damaged, causing it to run full-tilt.

 

You might be onto something. I just found a picture online that shows a fuse between the cable studs on the front of the PDC. When I replaced the battery cables I noticed a small, ghetto wire jumped across the studs. Not knowing there was supposed to be a fuse there, I didn't replace the jump wire that I'm now realizing was a ghetto fix for a blown alternator fuse.

 

Update. Figured out the overcharging issue. It was the lack of an alternator fuse. Alternator output is 14-15 volts depending on idles speed. Now the Gen light is intermittent, and it will almost idle on its own. Looks like I'm onto the next issue. Been working on finding and cleaning grounds. Wondering if anybody knows why the field terminals on the alternator and the coil are on the same circuit, if it is supposed to be that way, and any issues associated.

 

The bulk of the grounds are on the side of the engine block near the dipstick mount. I don't recall what year it started, but I think you also have a ground to the body next to the battery.

 

There's a couple harness grounds by the dipstick and the pcm. I installed a ground cable from the battery to fender. I also mounted my external regulator right there so it would have a good ground. Went back through and made sure all that was clean. You mentioned something about the coil maybe is shorted out?

 

I was thinking the field coil in the alternator shorted to ground could cause the alternator high voltage, but that seems to have been caused by the missing alternator fuse.

 

Oh I see what you mean. That is now bypassed with part of the external voltage regulator kit anyway. I've noticed that the ignition coil is on the same circuit as the wires for the field terminals. Gonna investigate this circuit some more