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Spastic Alternator


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Hello all...Slight problem tonite when starting engine, when the engine idled down after warming up some, lights came on in my dash..oil, battery, brake etc, but not CEL.. I put a meter on the battery and it was charging at about 12.7 at idle but the lights on dash were still on. When I increased the idle the lights went out and it was charging at about 13.5 or so. I let it idle again and no lights. I shut it off for a few minutes and started it again and at idle the lights came on again until I revved it some then they went out.. Do you think my alternator is going south??, or is it something else.. I did have a leaky PS valve about two months ago but I plugged the outlet and have had no trouble since.. Thanks for any input, Bobby

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I would turn on everything electrical you can and then measure battery voltage at idle. Headlights, blow motor, audio, bun warmers, rear window defrost, ...

If the voltage is sagging well below 13 VDC then the alternator isn’t keeping up and the battery will continually discharge.

Possible culprits are:

1) Loose/corroded wiring at battery or alternator charge line

2) Faulty alternator (likely worn out brushes that you can replace yourself). Well-documented problem of PS fluid damaging brushes. Need to fix leak at the same time though.

3) Slipping serpentine belt (you'd hear a lot of squealing if this were the case so less likely).

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Do the lights flicker at all during idle? Putting more load on the system as curiousB suggests is a good way to stress the system and find the weak link.

Keep in mind that sometimes it is difficult to measure the AC on the alternator such as what you might get if one (or more) of the rectification diodes is bad. And computers don't take kindly to AC. Also, the battery could be somewhat weak, aggravating the situation.

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The lights dont flicker no matter what I have on at any time, and the battery is about 6 mo old and is the most cranking power one I could buy.. If the alternator got soaked from the PS leak would it just be the brushes or something more serious? I just got home from work (11pm) so I will try to check the charging rate with everything on in the morning. If its less than around 13V you would guess its the alternator? My next step would probably be take it to Autozone and have them check the alternator with their equipment.. Thanks you both for your replies...Bobby By the way, I fixed the PS leak about 2 months ago, no problems since....

Do the lights flicker at all during idle? Putting more load on the system as curiousB suggests is a good way to stress the system and find the weak link.

Keep in mind that sometimes it is difficult to measure the AC on the alternator such as what you might get if one (or more) of the rectification diodes is bad. And computers don't take kindly to AC. Also, the battery could be somewhat weak, aggravating the situation.

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The alternator just needs a set of brushes. Cheap. The ATF melts the carbon brushes and that's why you have low output. At least that's what happened to my alternator as a result of the PS pump leak.

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