87 Accord alternator part 2

Alright, put in the new brushes, took the thing to the local shop...
their machine said it was all good. Shoehorned it back into the car and
fired it up...

I still get the charge light flickering, and the tach hovers around
7000-7500 although the engine isn't going that fast (actually around
2000-2500).

Am I missing some other critical component of the chargine system
somewhere in this car? It's not the ALT fuse; that checks fine, and
besides, it doubles with the fuel pump and the thing would run long at
all if that was gone.

 

at this point, id be checking all the wiring from the alt to the
battery, as well as the battery, engine, and alt ground straps, if so
equipped.

 

at this point, id be checking all the wiring from the alt to the
battery, as well as the battery, engine, and alt ground straps, if so
equipped.

 

Try looking around at idle with a DVM set on AC volts. Check across the
battery, from the battery positive lead to engine, and battery positive to
the chassis. They should all be less than .1 VAC (usually below .03 VAC). In
fact, the battery negative, the engine and the chassis should be firmly
connected together. If any of those readings are high, ensure there is a
good connection among those parts. Then if the voltage from the battery
positive to battery negative and engine ground look similar and high (above
about 1/2 VAC), it still means bad alternator - normally, a diode. The
absolute test is with a scope across those connections if you can get ahold
of one; diodes or bad windings appear as negative spikes with two much
smaller positive humps between them.

If you can't get any farther, the odds favor a bad alternator.

Mike

 

Try looking around at idle with a DVM set on AC volts. Check across the
battery, from the battery positive lead to engine, and battery positive to
the chassis. They should all be less than .1 VAC (usually below .03 VAC). In
fact, the battery negative, the engine and the chassis should be firmly
connected together. If any of those readings are high, ensure there is a
good connection among those parts. Then if the voltage from the battery
positive to battery negative and engine ground look similar and high (above
about 1/2 VAC), it still means bad alternator - normally, a diode. The
absolute test is with a scope across those connections if you can get ahold
of one; diodes or bad windings appear as negative spikes with two much
smaller positive humps between them.

If you can't get any farther, the odds favor a bad alternator.

Mike