Flaky alt.? Lots of info,please help daignose!

[dpok69]

I've been having the problem of the car not starting after driving and parking somewhere. This happens off and on since i owned the car. Also it always seems to happen when it is raining hard.I suspected my batt since i did not know about its history. I brought it to a shop and they said my charging system is fine.

Well today, while driving the car around my radio blanked out for a second and restarted. I checked my scanmaster reading for batt. voltage and it was 9.9-10.1v. I then shut off all the lights and accessories. I stopped for gas, but before i shut the car off i reved the engine for 30 seconds. When time to restart, car did not start!!! .

An attempt at battery boost was performed, but there was not enough juice to start the car. i though for sure my battery had an internal short or sumthing. There was a shop near by and i bought a battery. The car started instantly.

While driving back home i noticed SM volt. readings would go low sometimes and stay that way for a few seconds.

Here are some voltage measurements made from the battery using a digital volt meter with car idling:

All accessories on-->11.7v
Rear defrost shut off--> 12.0v
Headlights shut off--> 12.3v
Front window defroster shut off--> 13.3v
Car shutoff 12.7v

----Measurements made a second time----
All accessories on-->12.0v
Rear defrost shut off--> 12.3v
Headlights shut off--> 12.7v
Front window defroster shut off--> 13.88v
Car shutoff 12.7v

Defroster!!!!!!!! This explains why my battery dies in rainy weather usually. My alternator not upto the task anymore?

 

[GNFURY]

with a healthy charging system, you should get around 13 to 14+ volts at the battery with the car running.

 

[Tom Willard]

voltage too low. Time for a new alt. Good luck.

 

[Red Regal T]

I think you're having the problem of your battery not being charged because your volt light connection is intermittent. When you turn on the key, your volt lite should be on. If not, when you start your car, your battery will not be charged. Refer to your scanmaster, if it's not reading over 13 volts at all times, you're not charging. I also believe that the scanmaster reads about a volt lower than actually charging.......but that's another story.

 

[dpok69]

I checked my sm readings again while driving around. Its around 12.7-13.1 volts. When i turn on the front defroster, numbers jump around 12.3- 12.9 volts and hardly ever hits 13volts. Now this is all at slight acceleration. When i come to a red light, volts go lower to 11.7 to 12.3 volts with front defroster on.

I forgot that dam volt light is part of the circuit!!! That was a pretty stupid design by GM if the light goes out it does not charge. It should turn on when alt is not charging properly .
With key on ign position the volt light is on, when i start car it goes off.

Im leaning towards a new alternator, since it can not handle a higher current load when i have accesories on. Im thinking about kirbans chrome alternator (140amp) which comes out to $100 or so with exchange. ALso might as well upgrade the power feed to the alt also with lower guage wire..

 

[lrover2]

I believe the Kirbans alt is a 120 amp and it is $180 outright. I bought one a few months ago from them. Very very nice chrome job though.

 

[scottyb]

Take the alternator to Auto Crap, errr Auto Zone, and have it tested for free.

Also possible that the battery wires need to be replaced. I had a similar problem with another car. I replaced the battery and alternator, but after 2 weeks summer driving it would die still. Problem was that I was only getting 12 volts charge to the battery instead of the 14 volts that the alternator was making. That's not enough to re-charge after a start and running the fan on high (A/C). Cause was a corroded ground cable (internal) - $4.50.

 

[dpok69]

Damn! Kirban used to accept cores!

I guess i will have my alternator checked at autozone before i exchange it for a rebuilt one. They qouted me for $70 with core and $90 without.

This is for an '96 impalla alternator which is rated at 140 amps. They did have a screen on the computer that popped up and asked if case is 5 1/4 or 6 inches. I told them "6 thinking that 140 amp alt will have a bigger case. I gotta check my case size to make sure it is a direct bolt on.

As for power wires, i am definetly gonna upgrade them. Maybe even before i pull out the alternator. I found out that it is quite easy to polish aluminum with rotary tools and will go that path.