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Bad alternator? Autozone messing with my confidence...
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Stom
New User
Jun 4, 2008, 6:34 PM
Post #1 of 7
(11938 views)
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Bad alternator? Autozone messing with my confidence...
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New to the forums, thank you for the opportunity!
1991
Oldsmobile
silhouette
V6 3.1 Liter
130,000 miles
Ok here we go. My friend's minivan won't turn over. There's been a few electrical problems in the last few days. The windows wouldn't go up or down, the fan blower wouldn't work, and the engine stalled. This happened about two days ago, but we were able to drive it home. Now today, the engine wont turn over.
So I brought out my multimeter, and connected it to the battery. It read 10.95 volts - a bit low. So I jumped the van, and it started. Again, I grabbed my multimeter and connected it to the battery. Because I kept the jumper cables on for a few minutes, it read about 12 volts, but slowly trickled downward. I then connected it to the alternator, and there was no difference in the voltage. Again, it trickled downward - even if I revved the engine. That tells me that the alternator isn't putting out voltage, and needs to be replaced - at least that's been the case for every time I've ever worked on a car. But then I went to autozone.
I take the alternator out, and take it to one of the guys behind the counter. He puts it on their machine, and it checks out OK! I found that quite curious, so I had them check it again. They checked it several times, and each time it checked out OK. The guy then told me it could be the battery. However, that DOESN'T satisfy my question as to why the alternator wasn't putting out voltage. He couldn't answer that, and instead told me how he's been a mechanic longer than I've been alive.
Well, either one or two things is happening here. 1), their testing machine is completely worthless, or 2) what they're telling me is right. Now, mind you I've checked all the cables and connections for rust, corrosion, etc, and they're all OK. Am I doing something wrong here, or has anyone else had a similar experience at autozone?
Edit: I should note that when I managed to jump the car and get it running, you could hear the RPMs slowly deteriorate. To me, that would indicate the battery is proper and functional, however it's simply not getting a charge. Considering that the engine runs well after I have it jumped (albeit briefly), I would imagine the rest of the electrical system is OK.
(This post was edited by Stom on Jun 4, 2008, 6:44 PM)
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 5, 2008, 4:31 AM
Post #2 of 7
(11910 views)
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Re: Bad alternator? Autozone messing with my confidence...
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Charge and test the battery separately. Alt needs the battery and vs versa - it's a team effort.
Something just ain't right if you can only get a battery to read 10.95 volts so tend to that first,
T
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DanD
Veteran
/ Moderator
Jun 5, 2008, 4:35 AM
Post #3 of 7
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Re: Bad alternator? Autozone messing with my confidence...
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My first thought after reading your post; is why would they tell you it’s OK if it were not?
They’re in the business of selling parts; not free tests.
The alternator may not be getting the proper feeds from the vehicle to turn on?
We need to know which alternator was used on this vehicle. Gm used two different ones; an SI and a CS.
If you can tell us how many terminals there are at the plug in connector; that should be enough to figure out which alternator this is. Not the number of wires in the wiring harness plug but the actual alternator terminals.
The SI will only have two terminals the CS four.
But it would also be good to know what number of and color the wires are in the wiring harness.
A rule of thumb is that you’ll find battery (constant) power at one harness terminal and keyed (switched) power at another. The other two terminals of the CS alternator are there as sensing circuits for the computer or instrument cluster; depending on the options that this vehicle came with.
Dan.
Canadian "EH"
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Stom
New User
Jun 5, 2008, 6:51 AM
Post #4 of 7
(11901 views)
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Re: Bad alternator? Autozone messing with my confidence...
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I've brought starters down to autozone for testing purposes, only for them to tell me the unit worked OK when in reality it did not. I trust little of what Autozone has to say, and generally find that doing the opposite is more accurate.
In any case, the alternator is a rebuilt unit, a Delco Remy. It has 1 terminal. The harness has 4. I don't know the colors off hand, the car isn't near me at the moment.
I suppose the big question is this - is it possible to NOT see any voltage increase or output from the alternator if the battery is bad?
(This post was edited by Stom on Jun 5, 2008, 6:55 AM)
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DanD
Veteran
/ Moderator
Jun 5, 2008, 7:33 AM
Post #5 of 7
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Re: Bad alternator? Autozone messing with my confidence...
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LOL about autozone.
Batteries can be very deceiving; so I’m going to suggest that you start by following Tom’s advice and have the battery charged & tested.
Dan.
Canadian "EH"
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jkr25nlpaz
New User
May 18, 2009, 11:54 PM
Post #6 of 7
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Re: Bad alternator? Autozone messing with my confidence...
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okay so here's the deal ... my ma's got a 2001 Hyundai Sonata, battery light comes on. Only sensor to trip that light, is connected to alternator. Replaced bad battery, 2 days later car is dead. Jump her car, to get her out of circle k ... get her home. While car idleing it dies. Now my knowlede tells me that a running car is not consuming power from the battery, but is running off the alternator. Duh, change the alternator. But wait , 3 tests at autozone pass my alternator with flying colors. Old man River tells me, i have a short that is draining my battery while i drive, yet my battery only starts the car. So i think to myself, i bet that trusty autozone tester is not putting half the strain on that alternator as the car. I bet an alternator running at 50% would pass at Sh!tzone, but will leave my ma stranded at Circle K with a scratch ticket and a dead car. So i replace the alternator with a 120 dollar special at Penny Pincher with a lifetime, and low and behold ... no more dead battery, dim lights, lack of a radio ... even the power windows work. Good thing i didn't listen to the " Master Mechanics " at Autozone and tear apart the wire harness looking for that short ! Damn Yobbs !
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Hammer Time
Ultimate Carjunky
/ Moderator
May 19, 2009, 1:28 AM
Post #7 of 7
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Re: Bad alternator? Autozone messing with my confidence...
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This thread is a year old. If you have a new question and you can't find your answer in the archives, start a new question and someone will respond.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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