Intermitted Alternator or something ( 1992 vette)

[ReggieD]

Intermitted Alternator or something ( 1992 vette)

Had problem earlier, I thought I fixed it.

New Battery (1 week old)

New Alternator. (1 week old)

Problem still here.



While driving the voltage meter in the car erratically jumps from 14.1 volt to 12.2 or lower.

Sometimes the alternator can handle full load (AC on, headlights on, etc.) with no problem and still supply car with 14.2 volts. On other occasions the alternator will be putting out 14.2 volts once I turn on something (AC, brake lights, head lights, or etc.) the voltage begins to jump around and drop back to a lower voltage around 12.2 or lower.



I have no idea what the problem could be.

Can it be another bad alternator? I want to check other components within the car which might cause the problem. Keep in mind the battery is one day newer than the alternator. I measured 78 amps drawing from the alternator with the AC on, headlights on, hood lights, and radio. During this test the alternator was still putting out 14.2 volts. Tomorrow I try to get the car to repeat the failure of the voltage dropping to around 12.2 voltages. At that time I will re-measure the current draw at the alternator. This might help me find what the problem may be.
I purchased my alternator from "The Last Detail" in Atlanta GA. it's a AC Delco rebuilt. I paid $144.00. Do I need to spend more money fro a better one?


Any ideas

 

[ReggieD]

more

Upon the voltage dropping.
The dash showed 12.9
At battery 12.8v (+) (-)
At Alternator 12.9v (+) (frame of Alt)

New test (done later)
The dash showed (I forgot)
From battery (+) to Alternator (+) = 0.5v
From battery (-) to Alt frame (-) = NO Voltage drop.


In all cases of my testing the Alternator voltage has alway been very close to the battery voltage and dash voltage. Something is causing the alternator to put out lower voltages erratically. I can't determine what causes the tripping of this problem. It's Hard to repeat.

I tried to find the ground connection. VERY HARD TO FIND OR REACH.
I need ideas. I even try to find it by lifting up the car. How do I find this connection? I did find the jump start point located behind the battery.. It looked OK.

I will do more testing today before I replace the alternator.

 

[ReggieD]

I do not think its a wiring problem, here's why

Today..
Drove car...Car dash reads 14.1 to 14.2 constantly.
Load: AC, Radio.
Drive for about 20mins...Engine nice and hot.
Drive average 30 to 45 MPH.

PUNCH IT to 80 to 90 MPH for 10 to 15 seconds.
Problem back. Voltage drops..13v, 12.8, then 12.2.....
Drives back home about 3 miles @ 12.2 voltages.

AT Home...
Car dash reads 11.8 volts
Check current from battery (~20amps)
Check current from Alternator ( 0 amps)
Battery voltage read 11.9v (across battery post)
Alternator voltage reads 11.8v ( at alternator "+" and frame of alternator)

If I had a wiring problem the voltage across the battery would be ~12V and the alternator voltage would be ~14.2V. Since both devices are reading close to the same voltage indicates the wiring between the two are solid.
Something is causing the alternator to shut down (over-current, over-heat, or something) ALL I can think it to be is bad alternator or something in my car pulls a lot of current then shuts down the alternator.

 

[ReggieD]

Getting closer to a solution

I let car sit for 3 hours.
Re-started car.
Load: No AC, No radio,
Battery at 12.2v (42 amps measure )
Alternator at 12.2v ( 0 amps measure )

Drive around for about 10 mins.
45 to 60 mph.
Kept current meter on alternator.
Watched current 0amps, 1 amps, 4amps, 0amps
After 2 to 3 miles of driving, push it to higher speeds for about 3 seconds.
Instanteously dash voltages jumps to 13V then 14.2V
Now current is at 86 amps. Dash meter 14.2V
Drive home.
While car is sitting idle, I turn on AC, High beam, fog lights, radio, lower window. Current at alternator rise to ~110amps.
Next I raise the engine rpm and the current rises even higher.
THe alternator is rated at 124amps.
I think I am exceeding the rating of the alternator which causes it to shut down.
Is it a problem that my car is pulling this much current or is the alternator under-rated. Why is this a problem now?

Is there an internal circuit in the alternator that shuts down the alternator at over-current. What resets it?

 

[G Winter]

I hope you find the solution . I have the same problem with an old 82 chevy pickup . I have been thinking it could be a ground connection but can't seem to fix it .
Glenn