Just picked up an 89 IROC a week ago, and have been going through basic maintenance. The voltage is at 13.5 to 9 when the car runs. It's kinda random, but it doesn't vary quickly.

I had the charging system tested at a parts store, and the alternator charged outside of the car. When in the car was tested, the charging system was a bit too low, 11 something. So I thought it might be a bad diode in the alternator. The alternator passed in all tests on the machine. The car doesn't have any aftermarket parts, still has the original radio.

The car's voltage seems too low, even though I haven't noticed the lights dim at all. I'm used to my firebird's voltage running at a constant over 13 with 2 amps, 2 12's and 4 aftermarket speakers running with A/C and all the lights on without dimming on an autolite OEM replacement alternator. Is it normal for the voltometer to vary so much or do i have a deeper problem?

Forgot to mention that the battery also checked out healthy, and I've been able to drive it to work and school with lights and A/C without any problems.

 

Where are you seeing the voltage sag, the in dash gauge or by using a meter? It should not go to 9 volts while running. With a charged battery it would take a heck of a load to drop your battery voltage that low.

off car alternator tests are just a little short of worthless, I would encourage you to test voltage in the car when you are seeing the sag. Check at the alternator terminal and the battery. Be sure to check for bad connections.

 

dot know if this is helpful or not,but in my car, a 92 z, my alternator was constantly putting out low volts and it was because of a connection issue at the bottom of he column - apparently the regulator is controlled by those wires, at least thats the only thing i could come up with

 

what column?

 

the steering column

 

I agree check the voltage with a multimeter at the battery - first static(engine off)then with the car running but with nothing on.Static test should be at least 12.5VDC and running 12.8VDC to 13.4VDC.Only time you would see 9VDC would be during starting.You could still have a bad diode under load.Or it could be as simple as a loose connection,a battery cable breaking down(due to age).An aging belt,or tensioner,could be slipping but you would also notice cooling issues.

 

I've gotta check the wires then, cause the belt is fraying a bit but not slipping. I'm broke for now, so the belt is a later fix. No way my dash voltometer is just retarded or cross-eyed, right?

If it were breaking down, it would be at the ends, right? It wouldn't be corroded or messed up in the middle of the line unless the shielding were frayed,I think.

 

Cables can break down at any point but the ends are the most common.Heat and other underhood conditions are harsh on the wire harness in general.And then if you haven't replaced them yourself there's the factor of age.Resistance builds up in wires as they age(big factor for spark plug wires).

If the belt is fraying then you are not far from being left on the side of the road.Also if it's fraying then more than likely it's stretched.