Mechanics

CAR DIED WHEN I TURNED FAN ON

2002 Oldsmobile Alero • 130,000 miles

Fans stopped working so got it wired with toggle switch to make it thru until payday. Fuel pump went out last week and had it replaced. Now tonight it started up just fine headed down the road turned fan on low to help rear defrost clear my back window and car puttered a few times and died. It wont start again.
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Desertkiss22
June 12, 2012.



All of these problems could be related to a defective generator. Since the '87 model year GM has had a very poor design that creates huge voltage spikes. Those spikes can destroy the internal diodes and voltage regulator and can confuse the many computers on the car. With low system voltage the fuel pump won't run fast enough.

When one diode out of the six is defective you will lose two thirds of the generator's output capacity. That doesn't leave enough to run the fuel pump, ignition system, fuel injection system, heater fan, and a few lights. When you turn on too many things some of the computers will shut down and that can lead to engine stalling.

The place to start is by charging the battery with a battery charger set to the lowest rate for an hour, then have the charging system load tested by a mechanic. Your generator should typically be able to produce around 90 amps or more. If about 30 - 35 amps is all you can get you will also find "ripple" is very high. Most professional load testers display that as a relative bar graph, not as a voltage.

Low output current and high ripple is a sign of a bad diode inside the generator. It used to be real common to go through four to six generators in the life of a GM vehicle, but to reduce the number of repeat failures, replace the perfectly good battery at the same time. As they age, they lose their ability to dampen and absorb those harmful voltage spikes. The old battery will work fine in an '86 or older model. You shouldn't need to replace the battery if it is less than about two years old.

Caradiodoc
Jun 12, 2012.