Thread: Weird alternator problem

I would say hold on to what ever alts the store said was good trust their test. If you can borrow a battery that might be a good idea now. If the battery is only holding 11.5V that sounds like the problem right there.It should be 12-15V.

you should have left it in there thats probly the best one for you. It will level as you drive , shift ,AC , brake etc.

it will probly go to 14.5 V

Negative, I said it was at 11.5v when it was running. It was under load. It can't sit at 12-15v when nothing is charging it, all the while firing the ignition, illuminating lights, just after starting the car.

When the battery is just sitting there looking pretty, it was at 11.75 volts. The battery was shelfed since September in my cold, cold garage, so I don't expect it to be at 12v exactly. It still cranks strong and hard though, which is my basis for deeming it as not the problem.



On top of that, it was at 15volts and climbing. It was not holding steady, and it DEFINITELY was not going down, despite me turning on all accessories (wipers, lights, high beams, stereo, a/c). Also, normal operating range for the alternator is approximately 12.5 - 14.5 volts. Anything above that, as per the FSM is indicative of a bad voltage regulator (which as I understand it, is internal to the alt.)

If it is over 15.5V at 1500rpm that is bad but 15V that is okay. FSM says 13-15V O.K.

If you still want to put faith in that battery give it a good charging and test it's output again. Since it has been sitting and has seen a bad alt on it and it is cold. But if it is under 12V after charging FSM says N.G. Maybe just borrow a normal battery to see if that helps.
I just had and alternator die that took my wheelchair battery with it a week ago. Having to much power drained from the battery can mess some batteries up like it did mine.

I don't see why you can't just test the voltage difference across the alternator terminals (while it is not hooked into the wiring).. then you will know whether it works or not and can move on to check batteries, wiring, etc.

Better yet, if your alternator is working properly you can pull off the positive battery terminal while the car is running (as long as wires stay connected) and the car should keep running off the alternator.

I'm not really sure why anybody thinks its the battery at all. The car starts on its own with the battery, and the battery keeps the car running with no help at all from the alternator.

Danja, I did check the voltage across the alternator terminal. With the car running or not, its only showing 11.xx volts. The issue I am really having is that I have two alternators sitting here that should be working fine, but put out no voltage at all. Now it seems like you are saying to keep the alt on the car while the engine is running and then test the alternator itself to see if its putting out any charge, but why would that be any different than if it was wired up??

Lastly, if I disconnect the battery with the engine running, the car immediately dies.

I guess at the end of the day (or several days), I just can't believe that i have 2 bum alternators in my garage which were tested only minutes before to be working units.

I'm going to go exchange this stupid 1.6 alternator that I couldn't use back at the junkyard and get the correct 2.0 alternator.

If you don't disconnect it won't the battery voltage interfere? I don't really know it just seemed like it at first thought. Secondly if your car dies when the battery is disconnected then it has to be the alty or its wiring. And if you get output from the one bad one then it's probably the alternator.

Maybe you really did just get that unlucky.. but I'd say if the one you exchange it for doesn't work something tricky is at play.

To see if the alternator is good or bad, while the car is running disconnect the positive on the battery. If the car shuts off, your alternator is bad. Have you also tested the battery? With this cold weather and it sitting around will kill it pretty quickly!

Try checking the positive & negative battery harnesses for corrosion. If they're corroded inside the wires it can cause these types of problems. Also check the cells of the battery individually if it isn't sealed. One could be bad.

Problem solved, gentlemen. I couldn't believe it, but the alternator was no good. I brought it back to exchange it, and they bench tested it AGAIN, and still said it was good. I said I didn't care and wanted another one.

Car works fine now. I just realized something though, what I didn't post before, was that the whole time the battery + brake lights were on. No more!