nwoods
Expedition Leader
Okay guys, I replaced the alternator back in November 2014 per the recommendations of this thread, and the issue seemed to have gone away for a bit, then it resumed. So I replaced the alternator again in March 2015. Now it's reoccurring. This is crazy. I can't keep replacing alternators every 6 months. Well, I can, but I shouldn't have to. Clearly this is a bandaid for something more significant, and I think maybe I found it. But I'm an idiot when it comes to mechanical things, and particularly with electrical things, so let me report my findings and see what you guys think.
1. Battery with engine off: 12.75 volts
2. Battery with engine at low idle: 14.7 or so (fluctuates a fair amount between 14.2 and 14.8). Similar readings at high load (all lights, radio, ac on)
3. Battery tested at Sears, OKAY.
4. Alternator pulled, tested at Autozone, OKAY. Ran test 4 times, all OKAY
5. Alternator tested in car, under load by Sears, tested OKAY
6. As an experiment, pulled positive battery lead off terminal while engine was running. Voltage dropped to 13.75 rock steady, no flucuations. Interior lights stopped doing the disco fever thing. Everything was perfect, car ran great, all electrical readings totally solid.
7. Thinking that perhaps battery was bad after all, I swapped in new battery from another vehicle, no change, all disco fever symptoms remain.
8. Car dies a few hours after experiment. Won't idle, stalls at low idle. I later read on web that I might have nuked my ECU by running it without the battery in the loop.
9. Next day (today) take it to a local guy who says removing the battery terminal while running is really, REALLY bad, and probably just need to let the car idle for a while so that the ECU can remap it and learn how to keep the engine running again. (?)
10. Local guy connects a clamp thing to the positive lead and read amps off the alternator (bench tests only read voltage apparently). Amp readings all over the place. Positive 25 and negative 6 amps, fluctuating amperage is bad he says. Probably a bad alternator he says.
Now, it's possible I have been lucky enough to have 4 bad alternators in a row, but I suspect not. So I did some more digging. Found two helpful links about alternator circuit testing:
- http://www.aa1car.com/library/charging_checks.htm
- https://youtu.be/LGB6ZEjGm7Q
CRITICAL FACT: Instead of .2 volts, I am reading 14.x volts positive between the alternator housing and the positive battery terminal. When I read from the alternator output stud connection on back of alternator, and positive battery post when the engine is running, I get an odd negative 20 millivolts.
When i did the negative side ground circuit test, I got a similar high reading of -12.x volts, not the expected .2 volts or less.
Theory:
Do I have a bad cable from the alternator to the positive battery post? I ran an impedance (ohms) test on the cable and its 3.9ohms, and I get a tiny 3 to 4 millivolts with the engine off. This bewilders me. I don't know enough to connect the dots and figure out what's wrong.
Also, I checked impedance from negative terminal to ground post on fender, and its 0.0000, and between positive and negative terminal posts its O.L (totally open between posts, no connection)
I think my battery fine. I think my alternator is good. I think I have totally and utterly failed the Voltage drop test between alternator and battery, but I'm not sure what to do about it.
It appears that replacing that cable might require pulling the entire engine out.
1. Battery with engine off: 12.75 volts
2. Battery with engine at low idle: 14.7 or so (fluctuates a fair amount between 14.2 and 14.8). Similar readings at high load (all lights, radio, ac on)
3. Battery tested at Sears, OKAY.
4. Alternator pulled, tested at Autozone, OKAY. Ran test 4 times, all OKAY
5. Alternator tested in car, under load by Sears, tested OKAY
6. As an experiment, pulled positive battery lead off terminal while engine was running. Voltage dropped to 13.75 rock steady, no flucuations. Interior lights stopped doing the disco fever thing. Everything was perfect, car ran great, all electrical readings totally solid.
7. Thinking that perhaps battery was bad after all, I swapped in new battery from another vehicle, no change, all disco fever symptoms remain.
8. Car dies a few hours after experiment. Won't idle, stalls at low idle. I later read on web that I might have nuked my ECU by running it without the battery in the loop.
9. Next day (today) take it to a local guy who says removing the battery terminal while running is really, REALLY bad, and probably just need to let the car idle for a while so that the ECU can remap it and learn how to keep the engine running again. (?)
10. Local guy connects a clamp thing to the positive lead and read amps off the alternator (bench tests only read voltage apparently). Amp readings all over the place. Positive 25 and negative 6 amps, fluctuating amperage is bad he says. Probably a bad alternator he says.
Now, it's possible I have been lucky enough to have 4 bad alternators in a row, but I suspect not. So I did some more digging. Found two helpful links about alternator circuit testing:
- http://www.aa1car.com/library/charging_checks.htm
- https://youtu.be/LGB6ZEjGm7Q
CRITICAL FACT: Instead of .2 volts, I am reading 14.x volts positive between the alternator housing and the positive battery terminal. When I read from the alternator output stud connection on back of alternator, and positive battery post when the engine is running, I get an odd negative 20 millivolts.
When i did the negative side ground circuit test, I got a similar high reading of -12.x volts, not the expected .2 volts or less.
Theory:
Do I have a bad cable from the alternator to the positive battery post? I ran an impedance (ohms) test on the cable and its 3.9ohms, and I get a tiny 3 to 4 millivolts with the engine off. This bewilders me. I don't know enough to connect the dots and figure out what's wrong.
Also, I checked impedance from negative terminal to ground post on fender, and its 0.0000, and between positive and negative terminal posts its O.L (totally open between posts, no connection)
I think my battery fine. I think my alternator is good. I think I have totally and utterly failed the Voltage drop test between alternator and battery, but I'm not sure what to do about it.
It appears that replacing that cable might require pulling the entire engine out.
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