Ok, so my bone-stock '89 305tpi convertible iroc is acting kinda weird on me. My voltage meter reads that most of the time, I'm at just under 12 (figure 10 or 11), and frequently spend my time down around 8-9, which is WAY low. However, periodically it'll skyrocket up to bordering on the redline. While it's doing this (if I happen to have my headlights on) I can SEE the lights getting brighter/dimmer as the voltage jumps around.

I've had the alternator checked out, and my mechanic says it's fine... Is he wrong? Is there something else that could be doing this?

Thanks much all,
Damen

 

Assuming that your gauge is reading correctly I would have to say that the person that told you your alternator is fine is mistaking.

I have custom built alternator on my ride because I found any additions to the standard stock electrical system drained the power. Are you funning any extra electrical equipment - massive car stereo with multiple amps?

Observations-
1. Your volt meter will momentarily drop about two to three (maybe more on the two fan TPI) volts when your rad fan comes on; but it should recover almost instantaneously

2. You'll notice a substantial drop while both windows are being rolled down (assuming power windows)

3. When my stock alternator was in process of biting the dust it would periodically not produce voltage - thus my electrical system was drawing from battery - common to be around 8-10 volts. Though I never had a large spike in voltage...

Maybe that helps; I'd spend the aprox 125 bucks and swap the alternator - takes less than ten minutes...

 

All I have at the moment is a pretty basic cd player installed. No amp or anything. No drops when I just do things like roll down the windows or turn on the headlights. The drops/spikes seem to be completely at random (though I can hear whenever it changes in the way my car idles.. it's much smoother at higher voltages than at lower).

I figured it probably actually was the alternator, I just didnt want to blow the money on the wrong thing. Probably leave it as it is for a while tho. Been running it like this since October without it causing any actual problems, and I dont have a spar $125 laying around just now

Thanks

 

Check the voltage at the battery with the engine running...my dashboard voltmeter isn't very accurate. I'm going to check for voltage drops to the gauge, but haven't gotten around to it yet. My voltage at the battery is 13.9V, but inside the car it reads about 11-12V.

 

I've done that, and the meter shows the same low voltage (I've never left it on long enough to get a spike out of it).