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Old 09-20-2006, 12:12 PM
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alternator help

1996 Ford Ranger pickup....4 cly, 5 speed, with AC. All stock FOMOCO.....Problem: After driving a few minutes and killing the engine, upon resart, the charge gauge reads discharge. Sometimes it continues to discharge untill the battery is dead and the vehicle stops running. Sometimes it will jump back up to normal charge after driving awhile.

Diagnosis so far. Battery reads 12.8 (sitting, engine off)
When charging properly, battery reads 14.2
When gauge shows discharge, battery reads 11.6 (and
slowly drops lower and lower)
I have tried loading the system (i.e., turn on AC, radio, lights, flashers, etc., but no change.

Since the battery checks good and the alternator/regulator checks good (when charging), where do I go next. Is it possible to have a brush sticking in the alternator, or is someting not exciting the circut, etc.?

I know this is not a hot rod, but it is the only vehlicle i have to drive right now, as my 37 plymouth coupe is getting a front end rebuild. Thanks

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Old 09-20-2006, 01:29 PM
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Quote:
Originally Posted by 37 plymouth coupe
1996 Ford Ranger pickup....4 cly, 5 speed, with AC. All stock FOMOCO.....Problem: After driving a few minutes and killing the engine, upon resart, the charge gauge reads discharge. Sometimes it continues to discharge untill the battery is dead and the vehicle stops running. Sometimes it will jump back up to normal charge after driving awhile.

Diagnosis so far. Battery reads 12.8 (sitting, engine off)
When charging properly, battery reads 14.2
When gauge shows discharge, battery reads 11.6 (and
slowly drops lower and lower)
I have tried loading the system (i.e., turn on AC, radio, lights, flashers, etc., but no change.

Since the battery checks good and the alternator/regulator checks good (when charging), where do I go next. Is it possible to have a brush sticking in the alternator, or is someting not exciting the circut, etc.?

I know this is not a hot rod, but it is the only vehlicle i have to drive right now, as my 37 plymouth coupe is getting a front end rebuild. Thanks
"Charging Properly" at 14.2 sounds low to me, but I'm a partsman by trade ... not a technician. I believe it should be higher ... around 15.4 V.

Reduced output is usually due (I think) to a bad rectifier / diodes in the alternator. I suspect that this may also be what is causing the drain.

Take the alternator off, and into your local parts store. Most places can test them and recommend a replacement if bad. Again, some stores will "waive" the test fee if you buy a new unit. We used to charge $9.00 for a "bench test" on an integrally regulated alternator.

HTH,
Don
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Old 09-20-2006, 05:09 PM
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My 94 T-Bird was hving charging issues some time back
New Battery
Kept failing---would not start--every couple of days

had the alternator tested---good
did this about 4 times and FINALLY--the Alt wigged out while they were testing.

I was told something about a flakey diode inside

Changed the alt--car has worked fine ever since.

Bryan

Last edited by Bryan59EC; 09-20-2006 at 05:10 PM. Reason: misspelling
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Old 09-20-2006, 05:13 PM
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Doc here,

Next time it shows a drain, (duplicate the problem) , pull the wires from the alternator and see if it goes to zero..If so, you have a bad regulator Diode pack..(reverse biasing , or leaking backwards)

Either get a rebuild kit, or A new alternator..

If the drain does not change, pull a battery cable , with your DVOM set for AMPS and highest scale, place one probe on the cable the other on the battery and observe the reading, scale it back until the meter barely tops out the readout, this will be your true draw. If you have a computer, CD radio with active presets, Clock, alarm..it should read around 0.3 to 0.8 amps (less than an amp to be normal..If not:

If the fuse box is well marked pull all the fuses and relays, with your meter still hooked up, it should read zero..If so plug the fuses and relays back in until the current jumps up..follow that branch circuit, it is the offender, and repair / disable as required..

14.4 volts on a charging circuit is Perfect..exactly where it needs to be.

Doc
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