Maybe someone can help me out with this one.

I have a 87 IROC with a 5.7L. What is going on is when I stp at a stop light or stop sign the gaudge starts to read that the alternantor is only charging at or around 9-10 volts. And the dash and head lights will start to flicker alittle if they are on. It will happen with or without anything on except the motor. Whith my foot on the gas going down the road it is usually fine and stays at 13-14 volts. but once I stop it drops to like 9-10 volts. Usually it will make the lights flicker if I have the A/C on with the headlights. I have replaced the battery, and the alternator with no luck. And if it helps the alternantor is as hot as say the valve cover after I check it when I turn the car off after driving around. I don't know what else to check, I have done what I mentioned above and checked for bad grounds and found none. Any advice would be helpful.

Thanks in advance.

 

do you have an internal or external voltage regulator?? the regulator may be bad.

 

It is internal. I am starting to think it may be a bad new alternator. It wouldn't be the first time I bought a new part only to find out it was bad as well.

 

A new and good battery should hold 12V for hours of running without the alternator charging.. So if you get less than 10V immediately after making a stop, then I'd rather suspect there's a loose connection that responds to the torque and shaking of the engine. Check the ground wires between battery, - frame, - and engine, and the positive wires to and from the starter.

 

Not that it should make much of a difference, but everything is fine when the engine is cool, but once it gets hot is when the problem occurs.

 

Do you have access to a voltmeter?

Being able to check voltage across the battery, at the alternator, and where the alternator connects to the battery could be very beneficial to tracking down the issue.

As always, verify good secure connections between all electrical components, and since you're dealing with a belt driven accessory, verify belt tension.

 

 

All I have is a battery tester. Also i can't find any loose or corroded connections on the wires.

 

I have the same problem. I've got the voltage gauge in the dash showing the battery down to 10.5V when I'm idleling at a stop light with headlights ON and Rad Fan ON. While reading the actual voltage with my digital meter I've got 12V and when the gauge in the dashboard shows 13V, my digital meter reads 14V.
When voltage is low, my alt will whine but only when the alt is as hot as the valve covers (as you put it).
Replaced old alt with newly rebuilt alt, same problem, whining!
Rechecked newly rebuilt alt at the store where I bought it, Checked OK.
Tested battery, Checked OK
Tried a brand new battery (fully charged), same problem, whining!
Replaced alt belt, same problem, whining!
Loosen alt belt a bit, same problem,
I've checked all voltage drops, from lights -0.5V and rad fan -0.5V, the alt will recharge the battery up to 14V but only when it's hot, it'll whine.
If I take the Field Sensing terminal out of the alt, it stops whining. But then the alt is not working.
I'm also at a loss, I can't find a short anywhere, then again, I've got a lot of wires everywhere.
Let me know what you come up with.
Rob