[sideshowbob]

I've got a 92 Deville. I had a problem with the battery going dead. I had it tested and was told the battery and alternator were good. The starter was suggested. There have been quite a few times when I turned the key and the starter didn't engage, so I had known I was going to need to replace it. Well I did and the battery still went dead. I changed the battery and all was fine for a while. I went up town and the car died when I was slowing down for a turn. The lights dim when I hit the brakes and all the common bad alternator clues. I was wondering if it's possible for an alternator to test good and not be working right. Can an alternator fail intermittently? Any help is appreciated. I will replace it if it's bad. I have a winding sound when the engine is running and I think it's the alternator making the sound. Not sure of that though.

 

[Submariner409]

If the alternator/voltage regulator and battery have been tested and declared "good", then you're in the wiring troubleshoot mode. If the lights dim when the brakes are applied then either the voltage regulator (built into the alternator) or the wiring to the alternator is faulty. Same for the battery cables - both ends of both cables as well as the alternator connection for the heavy (red ?) wire - about 10 gauge - which carries charging current to a positive connection or block to charge the battery.

Every connection has to be clean and tight, with body grounds opened and cleaned, retightened, and shot with Boeshield or CRC Marine Corrosion Protector (looks like brown, runny wax).

If the alternator is whining as the engine runs, it is trying to charge something..........If the battery is more than 4 or even 5 years old, it's on its last legs.

 

[sideshowbob]

Well, I think I got it fixed. The battery terminals had quite a bit of corrosion on them. I got them cleaned and the lights don't dim no matter how much of a load I put on it. The winding sound I'm talking about sounds like a bad power steering pump. I don't think that's where the sound is coming from but it's that sort of sound.

 

[Submariner409]

Some alternators make a whining sound, particularly if they're cranking out a lot of volts and amps into a somewhat discharged battery. The 160 amp unit in my boat will wake the dead above 3000 rpm with all 3 batteries paralleled after a night of whooppee !!!

It's a high-pitched whine that rises and falls with engine speed. It may subside as the battery gets back near full charge again.

You should now see about 14.4 to 14.7 volts on your dash display (if equipped) at highway cruise.

 

[dchavezo]

Ive noticed a whining coming from my engine bay at highway speeds. new battery recently and all cables clean and tight.

I can really hear it when going under an overpass where the sound reflects off a flat plane above me (windows down). Battery and alternator were both tested and the battery was bad so I replaced it. Been hearing the sound before and after this. Im getting a solid 19 inches of vacuum from the throttle body so I dont think its a vac leak.

Alternator?
distributor?

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(oh also, if i press all the window up or down buttons the headlights do dim a tiny bit)

 

[still_walkin]

Ive noticed a whining coming from my engine bay at highway speeds. new battery recently and all cables clean and tight.

I can really hear it when going under an overpass where the sound reflects off a flat plane above me (windows down). Battery and alternator were both tested and the battery was bad so I replaced it. Been hearing the sound before and after this. Im getting a solid 19 inches of vacuum from the throttle body so I dont think its a vac leak.

Alternator?
distributor?

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(oh also, if i press all the window up or down buttons the headlights do dim a tiny bit)

any aftermarket equipment in the car