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Need your help on this one.

Burbdood 74

Burbdood 74

Giver of not a single damn...
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I'm hoping somebody can help. The wife has a 96 Pontiac Grand Am and for some reason the battery and the ABS lights are coming on. The battery light used to go out if you ran up the rpm's, but now it stays lit pretty constant. I pulled the alternator a month ago and had it tested at Napa and it passed just fine. It also has an 8 month old Die Hard Gold battery in it. Could the alt. be bad even though it tested ok? What else could it be? It's never drained the battery down to where I had to jump start the car, but it makes me nervous to see that light on.

Also, when the car is idleing, you can hear it go under load in an on/off/on/off manner. It's not a vacuum leak type of surge, but it just sounds like something is dragging the engine down like when you flip the switch on some heavy duty lights or something like that.

So what say y'all? I need help so I can get back to working on my stuff and not her's.
 
Sounds like teh a/c compressor is going on and off?

Could be alt related, especially with that light.
 
dhcomp said:
Sounds like teh a/c compressor is going on and off?

Could be alt related, especially with that light.
Click to expand...



I thought it was the AC compressor too, but it isn't. Is there a standard amperage that these alternators are tested for? What I mean is, do they test the total output or do they just check to see if it's putting out X amount of amps for the vehicle it's built for?
 
My very first thought was alternator until I read you just had it tested. Possibly a short somewhere?
 
nad said:
My very first thought was alternator until I read you just had it tested. Possibly a short somewhere?
Click to expand...

No, no shorts or loose wires, fusible links look good, but..........


I read in the repair manual that you can pull the wires off of the back of the alt. while it's running to verify the alternator is bad. According to Chilton, if the battery light goes off and the engine keeps running, it's the alternator. Well, I just did that and after 20 seconds, the car died. I tried to restart it and the battery is dead as a doornail. I've got it on a charger now. I hope I didn't screw it up by doing that.

My wife says that the light really comes on when she's running her heater and radio and such so I've got to think that it's the alternator not being able to keep up. Test or no, I *think* I'm just going to go with my gut on this and replace the alt.
 
I finally got the car started after the battery charger was on it for 5 minutes. As soon as I started it, the battery light lit up on me but the ABS light stayed off.
 
Did you check all the connections? It sounds to me like there is a bad connection in the charging circuit. Maybe corrosion in the cables? You don't even have to see it on the outside for it to completely kill a cable. And a simple voltmeter won't do it, as one good strand of copper will allow the minute amperage from a voltmeter to pass through and show no resistance.

Take the battery cables off and take them down to the auto parts store and have them check them out. They have to be load tested. I bet you those are the culprit.
 
noJeepshere said:
Did you check all the connections? It sounds to me like there is a bad connection in the charging circuit. Maybe corrosion in the cables? You don't even have to see it on the outside for it to completely kill a cable. And a simple voltmeter won't do it, as one good strand of copper will allow the minute amperage from a voltmeter to pass through and show no resistance.

Take the battery cables off and take them down to the auto parts store and have them check them out. They have to be load tested. I bet you those are the culprit.
Click to expand...


I replaced the positive cable when I got the new battery because the old one broke off in the old battery. I will check them out though. I hadn't thought about that.
 
A voltmeter will lie to you. However it would tell us if the neutron blender is putting any voltage back in the 12v storage device. The abs light is probaly coming on due to low voltage. Just cause the generator tested good in a bench tested single rpm range does not mean it is without fault.
 
Please grab a voltmeter from somewhere. Even a cheap digital one will do. Post back when you get it, and I should be able to talk (write?) you through a couple of checks that will tell you what the problem is.

Meanwhile, if the engine is cold, crank it up, turn on the lights and fan on full. Run it a couple of minutes like that.

Switch it off, and Carefully feel of the alternator pulley. If it is real hot, and the case is cool or lightly warm, your belt is slipping.

But get a voltmeter. With it, I can tell you if the Alt. is working, the cables are good or bad, tons of stuff.
Without it, not so much.

J.
 
To answer your question about testing, they test output but most likely could still miss an issue with the alternator. The testers used by most places just run at a single speed, usually higher than idle, and could miss a low voltage problem at lower RPM's. They also don't test for extended periods of time, which can show problems with bearings, bushings, or heat related issues.

Second, voltmeter is a must when diagnosing issues. Test the votage going to the alternator and make sure you are getting at least 12 volts to the main cable. Wires tend to corrode from the inside out, so it could easily be bad without showing any outward signs.

Finally, in most cases if either the alternator or battery goes, the other will follow closely. When I was working at my buddy's shop it was very common to see a car roll in for an alternator replacement and roll in a couple weeks later for a battery. If a weak battery is present it increases the load on the alternator. Weak alternator puts increased load on the battery. They work in conjunction so I just want to warn you.
 
Thanks for the replies so far guys! It looks like I get to go to Sears today and buy a new toy. If I haven't got this figured out by Monday, we'll be talking about the car she used to have.
 
UPDATE:


After much tool throwing and bad language, I went ahead and replaced the alternator today and that seems to have been the problem. After I had put the new one in, (with about 3" of room to work with), I started it up and the idle was nice and smooth and the battery light stayed off even after 20 minutes of running with the AC on full and the stereo on.

I never got a voltmeter to test it but I was told it's on my father's day good guy list. I want to thank all of you who responded. Now I get to work on my rig. :D
 
Glad to hear you found the cause. If Fathers Day doesn't bring a meter treat yourself. It is one of the first things I grab. So much that I have one at the shop and one at home. Not to mention the one in the trail box.
 
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