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Battery drain even after changing alternator twice

Tiny
AB AUTOMOTIVEREPAIR TRANSMISSIONS
  • MEMBER
  • 2000 CADILLAC DEVILLE
  • 4.6L
  • V8
  • AUTOMATIC
  • 108,415 MILES
We have changed the alternator twice and the battery is still being drained. Any idea of what is happening before we go in a third time?
Friday, November 29th, 2019 AT 7:39 AM

15 Replies

Tiny
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Good morning,

Do you mean the alternator is not charging the battery when running or do you mean the battery goes dead overnight?

https://www.2carpros.com/articles/how-to-check-a-car-alternator

https://www.2carpros.com/articles/car-battery-dead-overnight

Roy
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Friday, November 29th, 2019 AT 8:27 AM
Tiny
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Not charging why car is running.
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Friday, November 29th, 2019 AT 8:27 AM
Tiny
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Okay, I attached a wiring diagram for you to view.

Make sure the red and the orange wires are hot at all times.

If they are, the PCM controls turning on and off the alternator regulator as load increases.

Roy
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Friday, November 29th, 2019 AT 8:32 AM
Tiny
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It doesn't charge at idle.
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Friday, November 29th, 2019 AT 8:46 AM
Tiny
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Okay. What is the charge rate at idle and at 1,200 RPM's?

Roy
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Friday, November 29th, 2019 AT 8:47 AM
Tiny
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At 1,200 it wakes up and charges from 13.2 to 14.8 with no load, has new battery and rebuilt alternator, i'm going right now to check the ground underneath the backseat by the battery and I'm going to disconnect the ground on the frame by the engine, under 900 rpm it runs strictly on battery voltage and drops as low as 11.9, had my alternator re-builders check for battery drains and they tell me it has no battery drain, I repaired the oil leak at valve cover above alternator which was original cause of alternator going bad from hot oil leaking into it. I'm scratching my head it acts weird - it seems like PCM is turning it on a little too late. It does not react instantly to load- if I put a window down it dumps half a volt and needs rpm increase in order to respond to a load. Any help would be appreciated greatly, I also went ahead and put in a brand new belt.
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Friday, November 29th, 2019 AT 9:06 AM
Tiny
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Got it.

Just something simple, is the belt tensioner in good shape? The alternator is not slipping around the belt?

If all that is good, then looks like you need a PCM.

Roy
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Friday, November 29th, 2019 AT 9:37 AM
Tiny
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I cleaned ground on body by the battery. Removed paint, and cleaned battery positive terminal at battery, tightened everything up, still same song and dance, ordering a tensioner, and changing it as soon as possible, will touch base later. Thank you
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Friday, November 29th, 2019 AT 9:51 AM
Tiny
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You are welcome.

Keep me updated.

Roy
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Friday, November 29th, 2019 AT 9:53 AM
Tiny
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:( Just changed the tensioner, cleaned the alternator pulley, cleaned smooth idler pulley alt pulley is grooved, clean it off. It just does not charge at low rpm head lights are getting dim. Going to try an original Delco/Delphi alternator. I hope it's avail so I can have it done by tomorrow.
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Friday, November 29th, 2019 AT 3:09 PM
Tiny
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Sounds good.

Please use lower case for typing. It looks like you are yelling at me.

Roy
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Friday, November 29th, 2019 AT 3:14 PM
Tiny
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I'm so sorry definitely wasn't yelling, working on another project where it requires caps. Apologies
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Friday, November 29th, 2019 AT 3:20 PM
Tiny
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No worries at all.

Roy
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Friday, November 29th, 2019 AT 3:23 PM
Tiny
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Crazy business- my alternator guy would bench test unit at his shop, with all diff loads and speeds and let it run for 15 minutes to warm it up and swore to me it was good. I saw it with my own two eyes. I just finished putting in a rebuilt alt from a local jobber- Delco Remy made in Mexico and the charging system is working fine now. Steady voltage at diff RPM's and diff loads. Thank you so much for all your help. Happy motoring :)

Alex Barsanti- AB Automotive & Transmissions New Jersey- (a state with all four seasons)
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Saturday, November 30th, 2019 AT 1:41 PM
Tiny
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Good deal.

You are welcome.

Always glad to help.

Roy
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Saturday, November 30th, 2019 AT 1:48 PM

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