1996 4.3 GMC Jimmy voltage drops

My voltage gauge seems fine at idle & low rpms. The voltage drops when I turn on lights, ac & at higher rpms. I replaced the belt tensioner because the old one was weak. Had battery & alternator checked, both tested ok. Any ideas?

Use a good voltmeter, like a Fluke 87 and measure the actual voltage at the battery under different speeds just to verify the voltage is actually dropping. Then we can go from there.

eti engineer

It dropped from 15 to 13 volts, but the car was cold. It's worse on long runs when the engine is hot. I'll check it again when the engine is hot & see what the drop is. The belt looks good, but do you think it could stretch when hot?

Thanks for your help,
Dave

I have a somewhat similiar problem.

Not hijacking the thread, just will be interested to see what the outcome is.

My Voltage when the engine is cold and under normal driving conditions (Lights on, A/C on High,) reads 14.8 Volts across the batt terminals. This includes at idle or at a stop light.

After about 15 minutes of driving the voltage slowly drops down to a steady 13.8 volts. I assuming because there was need to charge up the battery.

I come to a stop light and the voltage drops to 12.8 and there is noticeable decline in the rpm of the ac blower.

I turn the A/C completely off...voltage jumps up to 13.8 Volts.

Battery, Alternator, Belt, Tensioner, ALL NEW.


Will be interesting to see how this issue progresses.

I have a somewhat similiar problem.

Not hijacking the thread, just will be interested to see what the outcome is.

My Voltage when the engine is cold and under normal driving conditions (Lights on, A/C on High,) reads 14.8 Volts across the batt terminals. This includes at idle or at a stop light.

After about 15 minutes of driving the voltage slowly drops down to a steady 13.8 volts. I assuming because there was need to charge up the battery.

I come to a stop light and the voltage drops to 12.8 and there is noticeable decline in the rpm of the ac blower.

I turn the A/C completely off...voltage jumps up to 13.8 Volts.

Battery, Alternator, Belt, Tensioner, ALL NEW.


Will be interesting to see how this issue progresses.
yours sounds like normal operation, i dont see any problem with your description

O.K., I gave up & took it to the garage. My battery had one dead cell, two weak cells, & three good cells. The battery tested o.k. when tested before, but when he tested the cells seperately he found the problem. A new battery fixed the problem.

Thanks for all the help,
Dave