2001 Chevrolet Silverado Voltage drop

Tiny
SFJ
  • MEMBER
  • 2001 CHEVROLET SILVERADO
  • 6.0L
  • V8
  • 4WD
  • AUTOMATIC
  • 100,000 MILES
The voltage drops off ( lights dim, fans slow down, etc ) and comes back up quickly. The problem happens when you do a short acceleration and let off gas, like driving up a street and stopping for the next stop sign. Does not happen every time. Can not get it to happen on a regular basis. Do not have issue when driving at high speed and come to stop. Battery is 1 year old. Cleaned all terminals and connections to alternator. Voltage at battery when engine is running is around 14.2 when a load was put on system ( AC, wipers, radio, lights ) voltage dropped to around 13.9/14.0 and stayed there. I am the only owner of this truck. This has happened off and on the life of the truck but seems to be doing it more often now.
Saturday, June 20th, 2015 AT 6:02 AM

6 Replies

Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
Is there any way you can hook up a meter and put it where you can see it and drive it and see what the voltage is doing when it happens? How is the belt? Does the alternator make any noises? Let me know what you find and we will go from there
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Saturday, June 20th, 2015 AT 6:48 AM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,004 POSTS
NOT TRYING TO BUTT IN, ONE MORE PIECE OF INFO MIGHT BE HELPFUL WHEN YOU RETURN WITH THE INFO FOR Racefan966

WHAT KINDA ENGINE RPMs ARE BEING TURNED AT THE SAME TIME THAT THE POWER IS GLITCHING ON YOU?

WHAT ARE THEY AT THE EXACT INSTANT THAT THE ACCESSORIES BEGAN TO ACT NORMAL?

THE MEDIC
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Saturday, June 20th, 2015 AT 9:30 AM
Tiny
SFJ
  • MEMBER
  • 3 POSTS
No way to really hook up meter and drive truck. With that said the volt meter in the dash is very close to the reading I got on my hand held meter. The rpms vary from time to time as to when this happens but I would say under 2000 all the times this happened. If I had to guess I would say the volts may drop to around just under 13 volts. Then climbs right back up. When driving the truck never see any kind of up and down on volts as the rpms change.
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Saturday, June 20th, 2015 AT 12:57 PM
Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
How many miles are on this alternator? How old is the belt and have you checked the pulleys for bearing noise?
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Sunday, June 21st, 2015 AT 8:23 AM
Tiny
SFJ
  • MEMBER
  • 3 POSTS
100000 on alternator. Belts and pulley tensioners were replaced about 6000 miles ago. Pulleys on each device were checked and seemed fine.
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Sunday, June 21st, 2015 AT 10:27 AM
Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
It almost sounds like it could be a warn bearing on the alternator. Have you tested the alternator out of the truck? I think I might. Nothing else makes any sense on this one.
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Monday, June 22nd, 2015 AT 8:24 AM

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