OK....

Took the alternator out of the firebird. When the car warmed up or I sat in traffice for more than 5 minutes the voltmeter in the dash showed the alternator putting out 8 volts and the lights (at night) would start to dim.

Took the alternator out and had it tested at the local auto parts store....tested (cold) at 13volts or so.

Guy says..tests fine.

I bought the only alternator they had in stock but kept the original core because it tested good just in case the is another explanation for the low output when warm. I can always return the one I just bought if I don't use it.

My observations. Once I get out of traffic and on the freeway the alternator was putting out at least 12volts, I'm assuming it's because it cooled down alittle on the open road. Does anybody know what else might be causing this or should I just throw the new alternator in?

Thanks for the advise!

marty

 

Weak batt, bad connection between alt and batt. Bad battery ground.
Diode inside alternator blown, which will decrease the avaliable current from the alt., but allow the voltage to read good once it's spinning good and the load is light.

Under-drive pulleys can cause similiar effects if installed.

First, check batt with a voltmeter to verify low voltage condition.

Automotive alternators were designed to live in a high temp enviroment. It's doubtfull that normal eng heat will have any noticeable effect on their performance.

Bad connections and corroded/damaged wires on the other hand, do get worse as they heat up.

Look for splices in the wire from the alt to the batt. They're a common failure item. Look for corosion under the insulation where alt wire connects to batt if you can.

 

Another issue.

Taking the alternator out kinda sucked. Two bolts were easy enough but I didn't see any way of releasing the tension on the belt to allow enough slack to drop the alternator out easily.....

Had to twist it a little. Am I missing an idler pulley or something?


Marty

 

your car (being an 88 model) has a full serpentine belt drive on it. the tension is maintained by a spring loaded tensioner. on the f-bodies, it is directly underneath the throttle body, towards the passenger's side.

you have to rotate the tensioner (counter-clockwise from what i remember)to release the tension on the belt. on my 88 s10, i was able to use a 1/2 inch ratchet to pull the tensioner back.
please, use the ratchet, don't try to pull it back with your hand, because the pulley on the tensioner spins freely, and i got my hand caught between the water pump and tensioner when it slipped.

 

THANKS.

The assistance is GREATLY appreciated!

Marty

 

And always disconnect the Battery cable before you get started!

 

I have a scar on the back of my left hand that is over 20 years old.

Reminds me to double check to make sure the battery is disconnected.

Thought it was....had my hand deep in the bowels of my engine. Tight fit..... Fiddling around the starter area..the starter cranked when I crossed the terminals and I jerked my hand out of the engine bay as fast as I could...SNAGGING EVERY SHARP THING ON THE WAY OUT. Ouch.