I have a 1990 Olds Cutlass Supreme SL 3.1 V6. My car went in the shop
about a month ago to replace a leaky intake gasket and head gasket. When I
got it back a very interesting scenerio developed the next day. Drove it
in town just fine. Drove about 20 minutes on the interstate, no problem.
A few minutes after getting back to in town driving, the charge light would
go on and off on the dash panel. Thinking my alternator was dying, I
checked the driver information center and saw I was spiking up 16, 17, 18
volts and going back down to 13.8-14.2 volts.
I got to where I was going, turned off the car, waited a few moments, turned it back on. No problem. Did some more in town driving, no problem. Went back on the interstate, no problem. Few minutes after leaving the interstate, overvolt spikes again. I brought it back to the shop the next day and they tested what they could and found no problems.
I can drive through it... typically only lasts a few minutes, but I don't like that idea.
I replaced the alternator with one from a junkyard and the exact same symptoms happened. I also replaced the computer. No change. What else can I look at or what should I tell the shop to fix?
I'm leaning towards two things. One: bad grounds. Check/clean all grounds
and battery terminals.
Two: A bad battery can cause this. Have it checked out.