How's everyone doing?? My son just bought a 95 Z28. Had it for 2 days and had to replace the battery and alternator due to charging problems. After some troubleshooting, I found that after the car gets warmed up the battery only gets @10 volts (gauge goes into the RED discharge area). If you break off idle it goes to @14.4 volts, let it back to idle it goes back in the red. The idle is @900rpm (according to factory tach). Since it is a used car I really dont know too much about it. Was told the opti-spark was replaced, a new tranny was installed with a stall convertor. The AIR pump was removed, but they removed the fuses and relay for it. The pulley on the original alt. is slightly larger then the one that was bought. My son swapped out the pulleys, keeping the one that came with the car. It's supposed to have underdrive pulleys,.
Will be starting to look over everything this weekend, any advice would be greatly appreciated, since I'am not that great with electrics!!!!

 

Sounds like the pulley is probably the culprit. Check the alt output with a good meter and if it is too low use the pulley that came with the replacement alt and see where that leaves you.

 

I have the same problem & suspect the Bosch rebuilt alternator. Bosch techline said the problem is "Normal" I will try a Delco rebuild as soon as I can.

 

I would put the original pulley back on the alternator(ie the stock pulley). I'm not a fan of underdrive pulleys. Since the voltage gets normal off idle I'm fairly certain that this is your problem. If the problem is not fixed after the swap, take the alternator back to the place of purchase for testing or exchange.

 

I replaced the alternator with a Delco rebuilt and it seems to be ok so far.