Brenden Rogers

1994 C4 Automatic

I had this problem pop up a little while ago. When ever i'm driving, you can see the display lights dim and the volt reading drop. It seems to be dependent on the the cars rpm. Cruising around at 2500-3000 rpm, the volts gauge reads around 12.5 - 13.7. When the rpm gets lower, you can see the volts pop back up to 14.5. There is also some flux when stopped at red lights, nothing crazy though.

I did a few tests with a volt meter at idle, and everything was showing fine. The alternator has a good ground, the battery shows its getting 14.5.

The car starts good and everything is fine. Any ideas on what to look at next?

65Z01

Do you have on heat/AC, head lights, brake lights, etc.? If running heater under climate control the AC compressor could be cycling.

At night my '88 will idle in the low 12s to hi 11s with brakes On. Then back to ~13.5 when moving.

Brenden Rogers

Actually no, everything was off expect for the radio. The brake lights don't seem to affect the voltage.

Before this, the car never dipped below 14.5. Isn't 11 and 12 a lower than normal voltage? I've always been told that a working alternator should stay above 14.2.

Thanks for your reply.

Churchkey

Possible sulfated battery suggest having it load tested.
@ 200 amps load for 15 seconds the battery should hold 10.6 V no less.
If the voltage drops below 10.6 during the test recharge @ 30 amps for 15 minutes then retest.
Monitor the charging voltage while charging if the charging voltage exceeds 16 V while charging
the battery is sulfated & could fail @ any time = you need a new one.

Good luck