Kmadr1

I had a low voltage problem the beginning of summer, start up voltage would read 13.8 but after engine warm up would drop to 11.4 to 12.5 on DIC. Could not get the car into my regular dealer so I took it to the dealer I purchased it from ( non Chevrolet) expecting to replace the alternator good thing I have a warranty. Dealer could not find any problems with battery or alternator, after much research they found a GM service bulletin where for some reason the Gages would go out of sync ( I did not find out the reason) after they reset gauges have not had a problem since, voltage reads 14.6 to 13.8 under load.

GCG

By any chance, do you have the technical bulletin number?

3sACROWD

Kmadr1

I will try to get more information from the dealer in the next couple of days and let you know

Kmadr1

I know, I said the same thing

elayhotajohnson

9-10-16 update: Ok i revcieved my replacement voltage regulator M530 on 9-6-16. Installed it into my GM original altenator and placed it onto the vette. Well i have not notice much improvment than before. The vlotage still drops to 12.9 at idle with AC and head lights on and the car is at temp. When car is cold I read 14.1v with AC and lights on. I can tell the gages seams to be close because the AC fan motor will change speeds when the voltage drops to 11.9. Now I can speed the idle (with my foot) and the voltage will climb. At speeds above 30, I read about 13.3 to 13.6v. for now I will just keep driving it to see if things improve. The voltage between the + battery and the + on the altenator to ground both read 12.3v. The voltage read between the + on the battery and the + on the altnator is zero.

sirdano

Here is your problem
on the altenator to ground both read 12.3v

Check what you get with car off at battery. If it is the same bad battery. Someone will post the bad voltage levels

gimp

Disagree, sirdano. Usually, even a moderately bad battery won't prevent the alternator output from being high. We know this because a good battery with, say, 12.7v, will still allow the alternator to put out a solid 14v. A battery is a complicated chemical device and doesn't simply limit the applied voltage across its terminals to its generating voltage.

However, if the alternator has been running at 12.3v, which is below good battery charge level, the battery will have slowly discharged until its internal voltage (chemical driven) was 12.3v - that is, pretty discharged.

The better test would be to turn the car off, hook up the battery to a battery tender, then the next day, turn off the tender, and check to see if the battery is properly charged up. A proper load test would be even better.

sirdano

12-30-2012, 01:15 PM #8
AlfredMay
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As stated by the gentleman from the Cumberland Plateau.... a new battery should register 12.8 volts when not being charged. The older it gets the lower the voltage will be. The chart below shows that your battery is dead It could also be that your volt meter is off....... or your battery still has a parasitic draw. None of this is good news.

State of Charge Specific Gravity Voltage
12V 6V
100% 1.265 12.7 6.3
75% 1.225 12.4 6.2
50% 1.190 12.2 6.1
25% 1.155 12.0 6.0
Discharged 1.120 11.9 6.0

GCG

Were these readings taken with the engine running, or with the engine off?

This test requires that measurements are taken with the engine running and, in your case, when it is at operating temperature, idling and showing low voltage.

gimp

That is correct, sirdano. But what you've missed is that if the alternator is running at 12.3v, the battery will become discharged, but not because it's bad.