Freefallin

For a while now my voltage has been on average around 12.9.

When the engine is cool like when I first start the car in the morning it is at 14.0-14.3.
A little later when the engine is nice and warm, the voltage will be between 12.5-13.5. Mostly between 12.5-13.0

*Reving the engine hardly makes any difference. It will probably go up 0.2 volts or nothing.
*I don't see any symptoms like headlights dimming.
*Battery is brand new. Tried 2 other batteries as well, same thing.
*Wires are all new. Both the + and - leads.

I'm checking the voltage both thru the instrument panel and a multimeter.

Now my question is...is this normal on a GTO or is my alternator failing...or is there some other problem?

GSAWYERS

Sounds like your alternator is weak. While checking voltage with a good meter, car warmed up and idling, turn on every accessory. If voltage drops into the 10-11 volt range you need an alternator. If voltage goes up or stays the same you're kinda ok. Your voltage is low compared to other cars, I've never tested a GTO charging system before. Good luck

99z28383

iTrader: (1)

I agree, your alternator is probably about to give up. Mine just did the other day and it was a slow process of the voltage getting lower till finally it put nothing out.

Freefallin

Ok folks! Just changed my alternator with another one from the junk yard, which looked pretty new, but the exact same thing is happening!

Any idea what's going on?

Freefallin

C'mon guys! Nobody on this one??
You must have monitored your voltage through that "holding-down-mode-and-set-button-while-turning-the-key-feature" at some point.

steamwalker

Mine's usually around 13.4. Did the junkyard not test the alternator before they sold it to you?

99z28383

iTrader: (1)

I bought one off eBay for like $80 from dB electrical. It's new, probably Chinese and working like a champ.

Freefallin

Haha! That's a joke! Around here, junk yard parts are more "as is". They do give you a guarantee thou...if it turns out to be defective, the hassle of installing and uninstalling is on you.

Freefallin

UPDATE: The voltage is dropping when the fans come on.
When they are not working, the voltage stays steady at 14.0-13.9.

Aside from the alternator, wires/connection and battery, what could be causing this?

Canada

iTrader: (2)

The GTO has a high parasitic draw. I'm seeing 12.9 also and have been. I haven't messed with the alternator, i think its the only stock part left but only have 50k miles on my car. I wouldn't worry too much about it but I would suggest picking up a battery tender.

Buzzmanb12

iTrader: (11)

That is normal voltage drop when the car is at idle or low rpm and the fans come on.

Grenade19

This. Try cleaning the ground points on the battery and car.

ViceCityPerformance

I had the same problem.

The alternator is not the problem. The battery cables are the issue. The cables are not thick enough to conduct the amount of electricity needed to feed the fans, accessories, AC, ect...

And as our cars get older the conductivity of our battery cables diminshes due to rust and deterioration.

The solution is to run an extra cable from the alternator to the battery and also add an extra grounding. It will improve the efficiency of the charging system.

On my car I run HIDs, Interior LEDs, Gauges, Headunit, upgraded sound system, back up cameras. All this with a 25% underdrive pulley and headers in the miami heat. My voltage now never drops below 13.4. After i did the extra cable and ground

svede1212

iTrader: (3)

It's normal for voltage to be high after starting as the battery is more discharged and the alternator puts out a higher voltage to charge it. After it replenishes it only needs a little above 12v to "trickle" charge it. I think mine is around 13V after it "recharges".