Alternating pitch whine accompanies voltage problems Reply Subscribed

Let me just say that I think I know what's wrong, I'd just like another opinion. Last night I noticed when sitting in the car, there was a whine that changed pitch with the RPM's of the engine. Today the voltage on my car was dropping so low that the USB fed stereo was dropping out. I think the issue is the alternator. I replaced it with a pre-owned one 5-7 years ago, so I think that one may now be reaching the end of it's life.

My question is, is it the alternator, or something else on the same belt that's causing the speed of the belt to drop so low that the voltage is dropping out? I looked at the belt while running and you can't hear the whine in the engine bay, only in the cabin. It's also not slipping as far as I can tell. There's no squealing, just the whine in the cabin. It sound like the sound you get when you start the car, only it doesn't go away after a couple seconds when the RPM's come down to idle.

Any ideas?

wmburns said:

Let me answer your questions with a question. Is there any evidence of belt material around any of the pulleys?

IMO it's not possible for a belt to slip so much that the speed of the acc are affected without leaving evidence of the slipping. This will be in the form of ground up rubber belt material.

Take the belt off and spin each of the accessories by hand. How do they feel?

A mechanic's stethoscope is your friend. The amount of information that such a cheap tool can provide has to be experienced to be believed.

Here's some more information that may help.

Howto perform charging system voltage drop test

Howto perform charging system voltage drop test

To anyone else reading any of my posts I usually include the line: Today's cars simply will not run right without a strong battery and charging system! Cut corners here at your own risk I'm a big believer in starting with the basics. As such I...

www.stangnet.com

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No, the belt pulleys all look clean and the belt itself still looks fairly new. I replaced it a couple years ago. The voltage will rise and fall with the RPM of the engine. I rev the engine, the voltage will return to normal (halfway between L and H), but if I let the engine RPM drop to idle, the voltage will drop almost to the L and the stereo head unit will drop out every few seconds. If I turn off the AC the dropping out stops and the voltage goes back to normal, but the whine remains. I think that's just the battery powering the stereo head unit now that the AC isn't draining the battery. I got a "new" (refurbished) alternator in the mail today, so I guess I'll find out for sure tonight.

wmburns said:

Let me answer your questions with a question. Is there any evidence of belt material around any of the pulleys?

IMO it's not possible for a belt to slip so much that the speed of the acc are affected without leaving evidence of the slipping. This will be in the form of ground up rubber belt material.

Take the belt off and spin each of the accessories by hand. How do they feel?

A mechanic's stethoscope is your friend. The amount of information that such a cheap tool can provide has to be experienced to be believed.

Here's some more information that may help.

Howto perform charging system voltage drop test

Howto perform charging system voltage drop test

To anyone else reading any of my posts I usually include the line: Today's cars simply will not run right without a strong battery and charging system! Cut corners here at your own risk I'm a big believer in starting with the basics. As such I...

www.stangnet.com

Click to expand...

Ok, I installed the new alternator and went to start the car, but I think the battery voltage is too low. The lights in the cabin would like up, as did the lights on the speedo cluster. It tried a couple cranks and then it went to that fast kind of "grinding/clicking" noise. I have a battery charger, maintainer, so I disconnected the battery and brought it inside and hooked it up. Unfortunately I live in an apartment complex, so I can't hook it up while on the car. I'm going to leave it on a 2A trickle charge overnight and hook it back up tomorrow.

Also, I'm pretty sure the alternator was causing the whine. I think the bearing on it is shot because it was making a strange noise when I spun the pulley/bearing after removing it from the car. The new one didn't make that noise when I spun it.

Just wanted to let you know that after taking my battery out of the car and putting it on a charger/maintainer overnight in my apartment, it started right up after the battery was reinstalled. Thanks for your help!