My buddy's '91 Cutlass Ciera 3.3L has a charging problem. The original alternator wasn't charging the battery, only showed 11.9 volts when running. Changed alternator, now overcharges at 16.7 volts and the check engine light is on w/ a high battery voltage code!!! What's going on, bad replacement alternator perhaps? Anything else that can cause overcharging? Battery starts the car fine. Battery cables seem to be ok.

Its probably the voltage regulator thats bad, theyre built in to those alternators IIRC, try replacing the alternator again.

Its probably the voltage regulator thats bad, theyre built in to those alternators IIRC, try replacing the alternator again.
Well I didn't know he was going to drive it to his work, but he did and it wouldn't start up after sitting for 8 hrs. So I went up to meet him and the battery was only showing 4.9 volts! So, I hooked my truck up to his battery and let it run for a while and then jumped his car. It started and ran fine by itself, but again the volts kept climbing into the 16v range. So we got it home and did some checks. The battery was showing 13.9 volts with the engine shut off and after about 10 mins. it dropped down to 12.95v, so I'm pretty sure the alternator is plain & simple not letting off on its charge. Also, the voltage drop from the alt. battery connection to the battery cable shows about a 0.4 v drop. I then used the jumper cables to connect the alt to the battery and it showed a 0.3 v drop, so not much change. Then I checked the batt. voltage at the alt. post and then at the battery and they both showed exactly 12.94v. Then checked using an engine ground instead of battery, again 12.94v, verifying a good battery ground connection. So I'm thinking another alternator will take care of the problem (crosses fingers). He is taking it in to Advance Auto to get it bench tested as I type this and will find out tomorrow if he has better luck w/ another one. Thanks for the reply.:cool:

you should be able to exchange it no problem, thoses things are rebuilt and sometimes you get a bad one. Its probably the voltage regulator, they used to be external back in the old days and you could replace them seperate but now theyre built into the alternators and arent servicable. Try replacing it and let me know if it fixes the problem.

you should be able to exchange it no problem, thoses things are rebuilt and sometimes you get a bad one. Its probably the voltage regulator, they used to be external back in the old days and you could replace them seperate but now theyre built into the alternators and arent servicable. Try replacing it and let me know if it fixes the problem.
They bench tested it and they said it was producing 17v, instead of the typical 14.4. So, he got another one. I'm afraid his battery may have gotten damaged out this ordeal. I will talk to him later today to see how the install went (I installed/removed it for him, but couldn't install this latest one as I had to get to bed to go to work today). I'll let you know if anything comes up...thanks.