MS Fowler

Is there a "normal" mode of failure for Jeep alternators?
My "volts" gauge went to 9 volts on the way home today. I wiggled the key, but it made no difference. I did not want to shut off the engine and restart as 9 volts won't make that happen.
As I pulled in, the radio went out, so I assume volts had dropped to less than 9. Turned it off in the driveway, and no start--only solenoid clicks.
Put the charger on it for a few minutes, and the battery tester showed OK under load. Charged it a few more minutes and it started right up, and volts went right to 13-14.
Do these alternators give some other signs before they fail, or is it time to replace it now?

Gee oh Dee

Is it getting really, really hot?

That's usually a bad sign.

scheetz_21

mine did the same thing! i made it an hr after it dropped of the rest of my 2 hr drive back to college.. and it just did it again today... so it is in the shop getting looked at now its really good friend of ours so he fixes stuff in exchange for wood lol!! fire wood.. and ill let ya know what he says..i put a new battery in mine when i got to school cuz my alternator tested fine when i had it tested...so if ya can wait ill let ya no lol

Blackolive

Yes, that's what happened to me three weeks ago. But it K.O.'d the battery in the process. I got the 9 volt reading and almost no lights.

MoZee

Same thing when mine went. I would go hit the s.o.b a couple tines and it was good, untill one day there was no more life in it

caged

see if a screwdriver sticks to it (alternator) like a magnet. if it sticks, it's good. no stick, no good.

Niac

That would be the brushes for the rotor sticking or probably worn out

Niac

The DC field is the rotor. The casing is an alternating field. I really doubt a screw driver would stick anywhere on the outside of an alternator.

The way to check is with a fully charged battery. Start the engine. Measure the volts with a meter and not the one on the dash. It should be between 13.5 and 14.5 volts across the battery.

scheetz_21

My PCM went bad!

MS Fowler

Thanks all.
I will slow charge all night, then tomorrow, I'll check the voltage at the battery before I start it. and while its running. If they are they same, then the alternator is not working.
I know this stuff---it sucks getting old--it jusr takes a while until the right answer bubbles to the surface.

caged

try it.

scheetz_21

I'd pull the alt. and get it tested much faster n easier.. And if not the alt. could be ur PCM like mine! Damn ..

MS Fowler

When I checked it in the morning, I had 13.0 volts on the battery. After starting the engine, I read 12.9 volts at the battery.
Calls for a new Alternator.
I replaced the Alternator--taking the old one with me to avoid the core charge, and to verify that the new Alt comes with pulley, and the bushing. Everything was attached.
About 45 minutes later, I was done 14.1 volts at the battery
Trouble shooting remains a basic skill.

jeep19xj91

My alternator let go on me 3 weeks ago. I left school and about 5 minutes on the road my battery light came on. A little over an hour later my speedometer quit working and the radio started popping and shut down. About 10 minutes later it began cutting, backfiring, and to summarize the story i sat along the highway for 3 hours while i waited for AAA to send the tow truck. Got home, new alternator, charged the battery back up, good as new.

MS Fowler

Its always a bad sign when the voltage is too low to operate the radio.