battery goes dead while car is in operation

1993 DODGE SPIRIT
135,000 MILES
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FRED4116
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When in the process of driving the battery indicator, battery has been replaced twice, indicates that the voltage is dropping and the check engine light comes on, the speedomotor goes to zero and then begins to operate again.
Car appears to be running only on the battery, but a mechanic who worked on the car said that it is not a problem with the alternator. What could the problem be if it is not the alternator.
Oct 28, 2011 at 10:54 PM
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CARADIODOC
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It IS likely the alternator. Intermittent problems have to be tested while the problem is occurring. If you have the little silver Nippendenso alternator, worn brushes are real common and real easy to repair, if you have the four cylinder engine. They can be replaced without removing the alternator from the engine.

Use an inexpensive digital voltmeter to measure the voltages on the two small terminals on the back of the unit. There will be a black plastic block with two terminals under two tiny nuts. Scratch through the rust on the nuts to take the readings. Those must be taken while the engine is running. One terminal will have full battery voltage. The other one should have less but not 0 volts. 4 - 11 volts is typical. If you find 0 volts only on the second terminal, the brushes are making intermittent contact. I can walk you through the repair procedure. You most likely won't find replacement brushes at the auto parts stores. I get mine from a local rebuilder. They might be available from the dealer too.

If you find full battery voltage on both wires, there is a break in the wire going to the voltage regulator inside the Engine Computer. The regulator could be defective too, but Chrysler had extremely little computer trouble back then.
Oct 30, 2011 at 6:04 AM