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fredr1980
01-23-2006, 03:17 AM
Long story short, I went 4 wheeling today out in Hollister Hills, ran a mud pit and I think I killed my alternator and messed up my charging system on my 97 Jeep ZJ 4.0L. My volt gauge normally sits at 14 and after running a mud pit it was sitting at about 11 and about a mile down the trail it finaly went below 9. I barely made it home (60 mile drive) on just the battery's charge. I went to the local parts store and picked up an alternator and swapped it out thinking that would solve the problem. Since my battery was dead after the drive I borrowed the one from my girlfriends truck to start my truck up. Well it started up fine but the volt meter was only sitting at 11 on a brand new battery, and as soon as I disconnected the battery my truck would die. Finally I got my girl to sit in the truck and give it some throttle to keep it from dieing while I swapped the batteries, which worked but as soon as I installed mine the volt meter dipped below 9 again and about 15 seconds later the truck died. Am I missing anything here? Is there anything else that could have gotten messed up in the mud that would prevent the alternator from charging? Any other ideas?

Thanks,
Fred R.
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Dragonfuel
01-23-2006, 11:32 AM
The voltage regulator is more than likely your problem. It is internally located in the PCM, so you have to replace the computer to correct.
I would strongly suggest have it double checked on a machine to verify.
Some places like autozone do it for free.

Dragonfuel
01-23-2006, 11:34 AM
Oh yeah... under your battery tray is heat temp sensor, this may also be telling the computer that the battery it too hot and confusing the computer to think it's over charging. It usually sets a trouble code or SES light

fredr1980
01-23-2006, 02:10 PM
Oh yeah... under your battery tray is heat temp sensor, this may also be telling the computer that the battery it too hot and confusing the computer to think it's over charging. It usually sets a trouble code or SES light

I don't think it's the heat temp sensor under the battery because when I removed it was all muddy and wet. I also went ahead and washed out the entire engine bay and sprayed everything electrical with WD40 to displace any water prior to installing the alternator but that did nothing. With regards to the PCM is it possible to have it tested by removing it and taking it over or do I have to have it in the truck when it gets tested? Also will a PCM from a 97 Jeep XJ 4.0L work since it is the same engine and year? I ask because I can get one for a great deal.

Thanks again,
Fred R.

grnd93
01-23-2006, 02:22 PM
Awhile back I had some trouble with my ZJ (not charging problems). I suspected the PCM, so I pulled it and had it tested. It came back as good. So yes, you can pull it and have it tested, but it takes a couple of days. My local Carquest is where i took it.

Dragonfuel
01-23-2006, 05:25 PM
The easiest way is to have it tested while in the Jeep. Sometimes you can get lucky at the stealership and have them do a quick test. By plugging in a DRB III and doing a quick test

fredr1980
01-27-2006, 11:42 PM
Well the Jeep is finally working right again and I don't know how it fixed itself!!! I went ahead and took the day off from work today to finally have my full attention focused on the jeep. I called my local Carquest and asked them if they could test my PCM and the guy pretended like he didn't know what I was talking about and told me the only places to test out PCM's was the dealership or shipping it back to the manufacture so they can test it out. Frustrated I finally called the stealership and they wanted $110 just to test out the PCM and if found faulter another $565 to replace it. Needless to say I did not go that route. I spend the entire day cleaning out EVERYTHING in the engine compartment, un-wraped cleaned & re-wraped electrical wires, cleaned starter and connections, battery posts, grounding wires, engine fuse box, disconnected PCM and removed it to check for water/mud damage. After I put everything back together and started her up I was STILL reading around 11 on the gauge :(. Finally I gave up and did some MORE research on the web and found that the voltage regulator giving out is fairly common in Jeep ZJ's, and I finally found one site that stated that the Trouble Shoot code #41 (An open or shorted condition in the generator field control circuit.) pops up if the voltage regulator has gone south meaning PCM replacement. So I went out again and since my battery is disconnected to conserve power (but unfortunately this also erased any error codes) I ran the engine about 5 minutes, checked the codes and got nothing. Then I remembered reading somewhere that you have to get the engine to normal opperating temp so the computer can read the codes so I took the truck around the block came back tried again and still nothing and still sitting at 11 on the gauge. So I decided to try one more time turned on the truck popped the hood and started looking everything over again and when I went back in the cab the voltage was sitting at 14!!! I turned the truck off and started it again to make sure it wasn't a fluke and even turned on the high-beam lights, ran the radio, heater, interior lights and rear window defrost and it stayed at 14. So I guess problem solved itself and I don't even know how. I just hope that I don't get stranded somewhere.

SORRY FOR THE LONG POST...
Fred R.