Overcharging Alternator 0n '81

[rockman]

Last week I was driving '81 vette and the battery basically blew up on her. I changed the battery and I noticed that the amp gauge was pegged above 18 amps while the car was running. By the time I got home the new battery was boiling. The alternator in the car was a Delco rebuilt unit and I took it in to test and it did the same thing on the test bench. I replaced the alternator this morning and the amp gauge pegged again with the same results. I am stumped as to what to check next.

The only out of the normal thing prior to this event was my brake light switch went out and I replaced it.
Other than that the car was running fine. Any insight or tips on trouble shooting would be appreciated.

 

[gmjunkie]

Last week I was driving '81 vette and the battery basically blew up on her. I changed the battery and I noticed that the amp gauge was pegged above 18 amps while the car was running. By the time I got home the new battery was boiling. The alternator in the car was a Delco rebuilt unit and I took it in to test and it did the same thing on the test bench. I replaced the alternator this morning and the amp gauge pegged again with the same results. I am stumped as to what to check next.

The only out of the normal thing prior to this event was my brake light switch went out and I replaced it.
Other than that the car was running fine. Any insight or tips on trouble shooting would be appreciated.

If I had to guess with out checking it out myself,I'd say you got a bad replacement alternator!! It happens allot more than it should!!

 

[Vettehead Mikey]

From the little that I know about the smoke tube system (the wires) on cars, your alternator needs to know what voltage is in the system so that it knows when to turn itself on or off- a reference signal so to speak.

Maybe that wire is broken/disconnected and all the smoke is leaking out on the ground.

 

[AKRAY4PLAY]

your voltage regulator is not working. either it's bad or the signal wires are bad. check the voltage coming off the main post to ground, it should be around 14.7 volts for all rpm. rev your motor a little while monitoring, i have seen bad regulators put out perfect numbers at idle and increase voltage with rpm. trace the wires going to the voltage regulator and and check them, if they are good, replace your regulator. also double check your grounds. a bad ground to the regulator will mess it up.

 

[gmjunkie]

your voltage regulator is not working. either it's bad or the signal wires are bad. check the voltage coming off the main post to ground, it should be around 14.7 volts for all rpm. rev your motor a little while monitoring, i have seen bad regulators put out perfect numbers at idle and increase voltage with rpm. trace the wires going to the voltage regulator and and check them, if they are good, replace your regulator. also double check your grounds. a bad ground to the regulator will mess it up.

An 81 has a Internal Regulator!! It's not like your 73 which has a external!! But he still should get around 14.5 volts at the Alt!!

 

[rockman]

Very weird

First wanted to thank you guys for taking time to answer and help with my dilemma. Here's the update...I took the alternator out and took it to a shop that actually rebuilds alternators, I figured they would be more objective. The alternator checked out ok and so did the voltage regulator. I went back home and started nosing around and looking for loose wires etc. as some of you suggested. I did not find any culprits but did find some wires such as the ones that go to my temp sensor that are quite brittle and candidates for replacement. I also found the ground cable from the starter to the frame to be in pretty extensive corroded state. I put the alternator back on and decided to give it one more try and sure as heck the alternator is working as it was prior to this issue. It still reads about 14 or 15 on my amp gauge but I checked the battery and at the alternator post and the readings are consistent. The best part is that the battery is not fizzing any more as it was when it appeared to be overcharged.

This of course is good news and bad news. It appears that the overcharging condition is no longer happening but...I don't know what I did to correct it. I suspect that poking around all the wires may have something to do with it and I really think that the starter to frame ground may be the biggest culprit, just not sure. I am going to replace it and hope that this takes care of it. Thanks again and I will keep you guys posted,

 

[rockman]

Final Solution

So after changing out every ground that I could find on the vette it came down to the alternator. I had to fight with the parts people since the alternator tested ok on no less than 3 testers at 3 different locations. Surely GM would not sell me a defective alternator...well as soon as they gave me another one - presto chango - new alternator charging at 14.5 volts. My gauge still reads high - close to 16 volts but I'm thinking that the gauge is fried.

Thanks for the input now I've got to change out my rear spring...can't wait!!!