Hi Guys, I have a 1989 GTA trans Am with a 5.7 TPI. I am on my third alternator in three years. I have a lifetime alternator warranty through Discount-advanced auto. The problem I am having is when I am driving at night, with the lights on, radio, AC, my gauge dips real low, especially in drive while stopped (at a light) I just put a new alt. in and it is doing the same thing. If I have all the accesories on and I am idling in drive (with the ebrake on) my electric meter reads about 12.44. In park it goes up to about 12.70. When I rev it a little it will go to about 13.05 (at night in park with accesories on) During the day with no accesories on it is about 13.69-14.00 under the hood with the meter. But even when it is there the gauge on the dash is slightly below 13. I guess my gauge on the dash isn't to accurate. But my meter is. When the car sits over night and I start it in the morning, the gauge on the dash is slightly over 13 for a few miles??? Then it drops slightly below 13. What is the problem?? Any alternator electrical gurus out there???? This **** is driving me crazy. Thanks in advance!!!
Also The aternator is 105 amp. Is there a bigger one that I can get? Discount-advanced auto only shows a 105 amp??
thanks!
Mike

 

What you are experiencing is pretty normal. GM has several TSB's regarding this situation. At idle with heavy accessory load the generator does not put out enough to handle the current load. You basically run off the battery. Battery capacity, state of charge and cleanliness of all connections all play into factor. Most generators only put out about 18-20 amps tops below 750rpm. Pull the guage out and clean the contacts, it's common for them to get dirty causing a low guage reading. Just try tapping on the guage face gently and see if it changes. It's also normal for the gen to throttle way up on a cold start then settle down as battery terminal voltage comes up. A larger gen may help a little but not as much as you think. I changed my 89 rock to a CS-130D which is the later version replacing the CS 130. The D uses a more aggressive charging curve and solved the same issues I was unhappy about. The guage is easy to pull out, clean the threads on the guage and the contact fingers it goes into. 105 amps is ample for the cars load. You can get higher capacity gens from places like www.alternatorparts.com however you will still have low output at anything below 750 rpm. A larger capacity battery is probably a more practical approach. Beware of chain store parts, an ACDelco part is still of superior quality.

 

Thanks Danno! I really appreciate the help! I gotta go to work, but I got a ZZ4 question for you later on.
Thanks again!

MIke