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1979-1993 & 94 Conv [Subscribe to Daily Digest] |
I have a problem with my 90 Saab 900s - after a really cold night, it started having intermittent electrical problems that I interpret as being charging problems.
With a reasonably fresh battery I can start the car and let it idle. The voltage light is off. If I measure the voltage at the battery, it looks good, between 13 and 14 volts. If I measure the voltages at the alternator I get battery voltage across the battery terminal and ground. Measuring the voltage across the alt's field voltage terminal and ground I get a voltage between 1 and 2 volts.
Based on the diagnostics described at http://www.swedishwrench.com/battery.htm, I'm not sure how to interpret this field voltage reading. The site says "You should find around 9 volts or so, but the main thing is you find some voltage" - it doesn't go into what a low reading means.
Anyway, the car will idle fine, and the voltage across the battery seems fine. The problem is when I start driving the car, after driving for a few minutes, once the RPMs are around 2.5k - 3, the voltage light will come on. Drop the RPMs and the voltage light will go off.
The belts seem tight enough, and as a test I adjusted them to be really tight, and it had no affect.
I've taken the alternator to AutoZone for a bench test. Their book didn't have the correct diagram in it, so the guy just tested it using the battery and ground terminals (the field voltage terminal wasn't hooked up), and it showed good voltage. I asked, but they didn't know the RPMs their test ran at.
I've taken out the voltage regulator and brush pack, and the brushes are plenty long and the springs are fine.
Anyone have any thoughts? Could a bad voltage regulator have this kind of affect?
Thanks in advance, Dale
posted by 24.61.2...
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