1991 Buick Regal • 82,300 miles

I am expierencing low voltage on my 1991 Buick Regal 3.8. I have replaced both the battery and altenator. While I am in the city volts gauge will suddenly drop and then pick back up. After being on the road for a few minutes it wilm read normal. But as I come to stop and take back off it will drop. When taking off and immediately stopping my car feels like it wants to. Stall out. Could this be a bad connection? Did I do something wrong? Before any of this it ran great. Now it feels like it has lost power.
November 4, 2012.

GM cars since the '87 models have had a very poor generator design that causes a lot of trouble. It is common to go through four to six of them in the life of the car, but you already did the best thing to reduce the number of those repeat failures. That is to replace the battery at the same time unless it is less than about two years old. In this case though, you have something else going on. These generators produce large voltage spikes that destroy the internal diodes and voltage regulator, (a good battery will dampen and absorb those spikes but they lose their ability to do that as they age), but those failures are almost always permanent.

You have an intermittent problem and any testing must be done while the problem is occurring. First of all look if the battery warning light turns on when the voltage drops. If it does, the voltage regulator knows there's a problem. If the light doesn't turn on, stop the engine, then turn the ignition switch back on. If the battery light does not turn on, there is a break in the wire going from the instrument cluster to it.

Restart the engine. If the warning light goes out but the gauge still shows low voltage, most likely the generator is working but the current isn't getting back to the battery. Measure the voltage at the battery and at the large bolted-on output terminal on the back of the generator. The two must be the same, and must be between 13.75 and 14.75 volts. If the generator voltage is higher, there is a break in that wire. Look for a large bolted-in fuse in the under-hood fuse box. Be sure those nuts are tight.

Another way to do the same thing is to stop the engine, then measure the voltage at the generator's output terminal. If you find 0 volts or something lower than the battery's voltage, there's a break in that wire or that fuse has a bad connection.

Nov 4, 2012.
Well I did as you said. I checked the voltage on both generator and battery, both outputs read the same but they gradually drop. Readings were about 13.95 then shortly after it starts decreasing. It seems to me like there is probably a short? Should there be anything else I need to overlook? All the wires seem to be in tact, but for some reason current won't stay flowing without interruption. My check gauge comes on when the current stops. But when its flowing normal the check gauge goes away.

It sure sounds like your new generator is defective. It could have one bad diode of the six. That will reduce its output current capacity to exactly one third of its rating. If it can only produce around 30 amps, that is not enough to run all the stuff on the car like the fuel pump, heater fan, lights, ignition system, and all the computers. The battery will have to make up the difference but the symptom would be the voltage is gradually falling. It isn't likely it would suddenly pop back up unless a diode has a bad connection. Shorted diodes don't suddenly get better.

The internal voltage regulator is another prime suspect but they too generally fail, then they're done for. They are rarely intermittent.

I would start with a load test but they would have to catch it while the problem is occurring. That will show if it can deliver the full typical 90 or more amps, and it will show "ripple". With one bad diode ripple will be very high and maximum output current will be real low. If the output is 0 amps, the voltage regulator is quitting intermittently.

Nov 6, 2012.
Well problem solved. New generator, However now I'm trouble starting my car. It turns over but it doesn't start immediately. It takes a few tries till it actually catches. But once over its fine. Im thinking starter is going bad? You can somewhat hear when it actually catches to turn over.