1991 Chevy S-10 electrical noise

Tiny
ROB M
  • MEMBER
  • 1991 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • MANUAL
  • 256,000 MILES
My high mileage 2.5 liter S-10 has developed a crackling/buzzing electrical sound that is heard through the stereo. The noise is much louder during deceleration and almost completely goes away when accelerating. There is no noise at idle. The noise does not appear to change in frequency but only in volume. When decelerating the volt meter on the dash drops to 12 volts and the dash lights dim. It does not matter if the stereo is on or not, the problem still persists.
The more accessories (wipers, signals, fan) That are turned on the worse the problem. The head lights are not, and do not affected by the problem.
Around the same time that the noise began the speedometer failed, so I replaced the instrument cluster with a used one and the noise still persisted
I have temporarily replaced the alternator and the computer(number and letter codes were matched) with used ones. This did not fix the problem.
I have checked the voltage at the battery and there is no loss of voltage during deceleration. The voltage at the fuse panel is also fine.
The stereo is aftermarket and was professionally installed 160000 miles ago. I have disconnected all power to the stereo and it did not change anything.
Several people have been baffled by this problem, I hope you can help.

Rob M.
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Friday, March 27th, 2009 AT 8:17 PM

5 Replies

Tiny
DOCFIXIT
  • EXPERT
Hi
You certainly have a strange problem. Check the battery grounds there is one at right headlight. The cable goes to engine check wire from it to cowl near wiper motor. See if all are tight and free of rust.
Let me know
Thanks for Donate
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Saturday, March 28th, 2009 AT 11:34 AM
Tiny
ROB M
  • MEMBER
I checked the ground connections. They are all good.
The problem seems to me like it might be related to vacuum. I disconnected the MAP sensor but the problems were still there.
The only thing strange to note was when I started the truck up after disconnecting and checking the grounds, the engine idle was very fast. I turned the engine off, put a jumper between terminal A & B on the ALDL, turned the key to "on" to look for a code but there was none, so I started the engine, and it ran fine. I removed the jumpers and everything is still ok. This has never happenned whenever I disconnected the negative on the battery.
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Saturday, March 28th, 2009 AT 7:50 PM
Tiny
DOCFIXIT
  • EXPERT
So you also had an idle problem as well as noise?
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Monday, March 30th, 2009 AT 4:32 PM
Tiny
ROB M
  • MEMBER
The idle problem appears fixed. I do not know if the computer can be reset but when I jumpered terminals A & B with the engine not running, then started the engine it ran fine. I removed the jumper and it seemed to have reset the computer.
You nailed the electrical noise with the grounding diagnosis. I revisited the ground on the back of the engine. The difficult one to clean. It was tight but was covered in oil. I cut the wires and moved the connection to a more accessable location. Problem gone.
THANKS
rob m
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Monday, March 30th, 2009 AT 7:17 PM
Tiny
DOCFIXIT
  • EXPERT
Glad to hear all is well You may have cleared a stored code in ECM and corrected idle.
Hope no more problems
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Wednesday, April 1st, 2009 AT 8:01 AM

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