I've been trolling these forums for a few months, and up until this point I have been able to find all the help I need without ever having to post my particular problems. I've had no such luck with my most recent alternator problem, so hopefully someone can help me out.

About two weeks ago my alternator crapped out while I was in the middle of diagnosing a fuel pump issue. I had the car idling for a good 45 minutes when I noticed that the volt reading was way low, at about 10 or 11. After some poking around under the hood, I determined that the alternator was not charging. I pulled it and rebuilt it (I'm in college and broke), replacing the bearings, diodes, regulator, and brushes. After I installed it and started her up, the gauge reading stayed at battery voltage. I was a little confused (and very pissed off, the p/s pump pulley had been a real p.i.t.a.) but I continued to let it idle for a few minutes. I hooked up my DMM to get a better reading of the voltage, and it was just sitting at 11.5. After about two minutes, the voltage jump to 14.5, then right back down to 11.5, like the alternator kicked in for a second, then cut out. It jumped again two or three times, then it stayed at 14.5 for the rest of the time I had it on. I drove it around for an hour or so and it seemed normal.

The next day the same thing happened, and has happened ever since. I start it up, the voltage it aroud 11.5-12, it jumps up a few times, then finally settles in at ~14 volts after a few minutes idling. I've not been able to find anything wrong the wiring or connections and at this point I'm still confused.

Has anyone experienced anything like this before?

BTW it's a 92 TBI RS

 

I am goin thru the same problem kind of my alternator won't charge my battery my volt meter is low I took the alternator off got it tested it check out good I jumped it with my other car and my battery meter jumped up to 14-15 I don't know what's going either lost o_O its a 92 camaro by the way

 

Have either of you converted your pulley''s? I am going through the same thing. The volts drop at idle and all electrical components run sluggish i.e. lights, wipers, windows, door locks... I checked everything - alternator, cables, grounds etc. It turns out the problem may be caused by a pulley serpentine conversion I did when I dropped a replacement crate engine. The new performance crank pulley is smaller in diameter 5 1/4". This makes the belts spin slower. Consequently, the volts at idle drop and the car runs hotter in the summer. I just ordered a 7" diameter crank pulley set to replace the ones currently on the car. I will let you guys know how it turns out.

 

Bbraves7: I assume you have the stock 3-wire alt, and that you have checked the cable to batt + and alt ground are solid. Check them again, especially all engine grounds. Then - have you checked for connection of the 2 smaller wires?

The red one on alt terminal '2' should have constant 12v. The brown wire on terminal '1' should have 12v on it in ign run, supplied thru the idiot light if you have one or resistance wire if you have a volts gauge. If either of these two is not connected, the alt won't charge. Maybe one of them may be intermittent.

 

Thanks for the reply TreeFiddy. I have checked the bat. cable and grounds numerous times and they are all good. I was doing some work on the car yesterday and this is what I found.

When I started the car up the alternator was not charging according to the volts gague on the dash, and confirmed by my DMM. I shut it off and tested the brown wire (P terminal IIRC) and the red wire on the alt. connector. The red wire had battery voltage at all times, and the brown wire had battery voltage when the ignition was in the run position. I plugged it back in and started it again. Still not charging. I let it run for a few minutes and it eventually started charging.

According to what you have said (and also the service manual), everything seems to be operating normally. This makes me think that either the voltage regulator is bad, or there's something screwy going on with the windings. I did replace the regulator when I rebuilt it, but I've read plenty of stories on here about people getting faulty "new" parts.

Is there anything else I can check? Should I back probe the brown wire while it's running to make sure the regulator is getting 12v when the engine is running?

 

Yep, measure while running - that's when the fault is occurring, might still be something oddball with the wiring. If the wiring's good, like u said the next guess would be regulator or brushes/windings, but you've already been there. Does it always kick in after a couple of minutes?

 

I'll see if I can get out there later today and test it while it's running. It's been raining the last two days so hopefully it will let up soon.

It always kicks in after a couple of minutes. It never takes longer then four or five minutes, just long enough for the temp gauge to start moving.

 

I went out this morning and back probed the brown wire while the car was running and the alternator was not charging. It had battery voltage the entire time. I left the dmm on the alternator to see how long it would take to start charging and after about 7 minutes nothing happened (it has never taken that long before). As soon as I put it in drive, the volt gauge shot up and it was fine after that. Could it be belt slippage that's causing it? I checked the belt when I put the alternator on, and it seemed ok (no cracks or anything). How do I check for slippage?

 

I doubt it, would have to be a helluva slippage and theres no squealing, smoking, vibration or other signs of belt distress (is there?). The off/on and predictable nature of the problem sounds most likely electrical.

Out of curiousity, does putting it in drive fix it every time?

Wiring sounds fine, sounds most likely the regulator's bought it. Can u get a cheap jy one to compare?

 

Nope, no squealing, smoking etc. As far as putting it in drive fixing it every time, I'm not sure. Usually I let it run for a few minutes before I have to leave and by the time I get in the car its good to go. A few times I have just gotten in and driven it without letting it warm up, and it acts even weirder. I think at this point I'm just going to throw a new alternator (or at least a known good one) in and see what happens. Thanks for all your help. I'll make sure to post what happens after I swap it out.

 

My jeep does the same thing every now and again while sitting at a light. All I did is stab the gas to rev it up, and the alternator "wakes up". Have you tried upping the rev's while it's not charging?

What I understand is that when the Regulator goes out, the voltage output increases. Did you clean the brushes and the stator real well?

 

Yeah sometimes if it's not charging I'll stab it and it will kick on for a second and then go down again. I changed the brushes when I rebuilt it. As far as cleaning the stator, the only thing I did was wipe it off. I did test both the stator and rotor for shorts and they were both fine.

 

So just to close this up, I wanted to post my solution. It turned out that the wire going from the battery to the junction box by the radiator was toast. After almost 20 years, corrosion go the best of it. I found out what it was when I was messing around with the battery cable and realized that whenever I moved it around even the tiniest bit, I could here all the relays click on. Once I narrowed it down to the junction wire, the repair was pretty easy. I picked up a new battery cable from autozone that had the junction wire built in. I soldered and skrink wrapped that bad boy (junction wire) so hopefully it will stand up to another 20 years. While I was at it I replaced the alternator cable with a 4 AWG section that I had already. The lights are definitely brighter and it charges every time as soon as I start it. Thanks for everyones help who posted on here.