Had a problem the other day, where my battery was failing to charge and the engine shut down while running, i had to get it jumped and keep pumping the gas just to get it down the street, but it would still quit at a stoplight and couldnt get it started without a jump

took the alternator out, got it tested, the computer said it was OK. I also replaced my negative battery cable because the plug was actually cracked so it was not a complete circle around the post.

charged the battery and it seems to be maintaining good voltage with not much load.

my only theory is that perhaps my fan clutch has gone and is putting resistance on the belt, which isn't allowing the alternator to spin quickly enough.

ill try spinning the mechanical fan when its cold tomorow, should it be able to spin without the engine running or not?

 

Charge the battery overnight and have it tested at the parts store.

 

You should be able to spin the fan with the engine off. What is the charging voltage with the engine running? It should run after being jumped unless the battery has a bad cell or something. Have the battery tested.

 

I had the same problem and I replaced all the cables from batt to alt to starter, both power and grounds. How ever i did do larger wire cause i was planning to upgrade anyway. Also the grounding stud on the fender was rusting through its welds.

 

I had the same problem when I got my XJ. It was a bad battery. It was a pretty new battery. I took it back to NAPA & got a free replacement. About a year later I put a alternator on it. Not sure if the two were related.

 

This. Battery has a dead cell. It'll say 12V +/- 10% but the current is garbage.

 

I kept going through batteries that's why I changed my cables, alt kept checking good. Batts would check bad.

 

My voltage stayed the same the following morning and it seems to stay charged when driving around, guess ill just keep an eye on it.

I think replacing the negative cable and giving the posts a good cleaning was all it needed.

 

If you keep having your battery going dead if it sits for awhile you may have a parasitic draw. If so check out the video I attached. It will tell you how to locate it. I know the video helped me out.

 

my problem came back, right at the end of a work day the alternator just quits. It had been working correctly for about 4 hours straight, but eventually my battery starts dying and eventually the car won't run.

it seems to work in the mornings but not once the engine has been working for a while. The engine should still have plenty of voltage without a working battery, so im pretty sure this is a problem with the alternator, or perhaps wiring. Its an intermittent problem so nailing down the exact cause is hard.

like i said i took the alt to oreilly and they said it was putting out a steady 14 volts.

 

day 3 of this problem, had the battery tested finally. battery checked out OK.
Used a circuit tester and all of my fuses look good. So now im thinking its either the voltage regulator in the PCM that has failed or the battery temperature sensor is telling the PCM that my battery is about to boil when its actually not. the battery temp sensor can actually throttle the alternator's output.

next thing im going to try is cleaning all of the alternator's connections, then put a new temp sensor in, and if that doesn't work then ill try a new alternator (because its a quick swap, and free). and then ultimately ill try swapping a PCM.

although its sad, i never thought you could brick a jeep

 

Before you start throwing parts at it clean all the electrical grounds, it's free and more than likely the root cause of the problem. Also important be on the lookout for green corroded wires and/or connections.

 

I ended up putting in a new alternator last week and it fixed my problem, so in the end it was brush contact that failed most likely.

although now i have a new problem, the alternator (im almost sure) likes to squeak when the engine is cold, and I don't believe i put the belt on too tightly.

 

You probably didn't put the belt on tight enough. The 4.0 likes the belt stupidly tight.

 

I think its the alt. i bought a remanufactured alt with a lifetime warranty. ran lovely after i installed it. The next morning it squeaks until the engine warms up and its still squeaking.

best guess is the pulley bearing.