Thread: Odd voltage issues

Base info: 1999 Buick Regal GS.

Lately ive noticed a trend in how my car runs. On a cold start the voltage is fine(14.5 volts). However after a trip (short or long trip gives the same results) ill start the car again and my voltage stays around 11.5 volts and after about 10-15 mins of normal driving it bumps back up to normal. Any ideas guys?

cold start raises the rpm's making the alt spin faster raising the alt volts, warmed up at idle its lower rpm nets less volts.

pretty common for a gm alt.

why would the voltage be so low though? Even if i get down on the car a bit to spin it faster it still takes a bit to charge back up.

your battery could be on the weak side.

Yeah could be. its a 6 year old optima that was ran at 15+ volts for most of its life

dirty terminals or a bad cable also come to mind.

My GP will pull down to 11.5 every now and again, but not very often. Usually when letting off from light throttle, like coasting/pulling into a driveway. I can get it to do it consistently if I ever so slowly try to feather the throttle just off-idle. As I slowly press the throttle, initially I can see the rpms increase slightly (50 rpm) then back to idle (as if Im not pressing the throttle), then as I increase the throttle a little more the motor finally responds. Then as soon as I let off, it surges at 550-650rpm at 11.5 volts for 5-8 sec b4 it recovers back to 750 rpm/14+ volts.

Its done this ever since I had the car (5yrs) and I've had 5 different alts, 2 97-98 cs130's, 1 99-03 cs130, 2 AD244's all of them did the same thing (not the reason for replacements only one alt actually died). In my case its not a rectifier or VR issue, I think its either the sensing wire, or the PCM itself. I notice if I unplug my sensing wire and plug it back in while its running, it does the same thing, it pulls the rpm and voltage way down while it tries to stabilize. All my connections are clean, 0awg big 3, battery is a 3y/o Diehard platinum with a 12.6 surface charge. Ive given up with that gremlin.