My car is getting fairly old but still runs.

ANONYMOUS

MEMBER
1995 PONTIAC GRAND PRIX
180,000 MILES

My car is getting fairly old but still runs pretty good. I had the starter replaced but then I was having problems with it continuously dying on me while I was driving. It seemed to only do it when it was hot out and I came to a stop. I had the battery and alternator replaced. Because neither seemed to fixed the problem. The car sat for a few months before I was able to drive it again and then I changed the spark plugs, oil filter/oil, and air filter. It seemed to run fine until I drove it at night. The lights started to flicker on and off and the interior lights were doing the same or at least getting very dim. The lights on my car dim whenever I use the power windows or cruise control. I get very scared about driving at night considering my lights turn on and off by themselves whenever I run the radio, heater, dashboard lights, or cruise control. I was told it was probably the alternator but I just replaced it and it cant have more then 300 miles on it at this point. It seems to be getting better sometimes but other days I have to drive with no interior lights in the cold with no radio. I hate to keep driving it like this but no one can tell me what could be wrong. Any thoughts? I have gotten many suggestions everywhere from a little sensor to an ignition module to a fuel pump. The service engine light is not on. The only light that comes on is the low coolant and that I know is just a faulty sensor. I would really appreciate any help!

1 Reply

CARADIODOC

MECHANIC
33,741 POSTS

Have the generator load-tested. I suspect you're going to find it can only develop exactly one third of its rated output current, and "ripple" will be very high.

When one of the six diodes fails, "ripple" will be very high and the unit will only be able to produce exactly one third of its rated output current. That's not enough to meet the demands of the electrical system under all conditions. This is a real common problem on GM vehicles and you can expect to go through four to six generators in the life of the car. To reduce the number of repeat failures, replace the battery at the same time, which you already did, unless it is less than about two years old. Due to their design, these generators produce huge voltage spikes that can destroy the internal diodes and voltage regulator, and interfere with the many computers on the car. As the battery ages it loses its ability to dampen and absorb those spikes.