Fox Mustangs 1979-1993 Mustangs Member Tech & Restoration Discussion

Acceleration causing battery voltage to go down and car dies

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Old Feb 29, 2012 | 03:27 PM
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Acceleration causing battery voltage to go down and car dies

Could it be the belt tenchoner or something in the alternator? The alternator has been tested and it's fine
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Old Feb 29, 2012 | 04:51 PM
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welcome to TMS! Was your alt tested in the car or did you take it somewhere to have it tested? How was it tested?
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Old Feb 29, 2012 | 06:21 PM
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Originally Posted by Glenn
welcome to TMS! Was your alt tested in the car or did you take it somewhere to have it tested? How was it tested?
I had it tested by a friend. He said it could be the belt or the tenchoner is that true
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Old Feb 29, 2012 | 09:33 PM
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The belt *could* be slipping. But you'd also notice the power steering sucked and your A/C wasn't working, if not hear a squeal as it stopped working.

The tensioner *could* be broken... you would have noticed that as either a snapped belt (overtensioning) or a thrown belt (the tensioner is way-loose and it throws the belt. Also noise, or jumping about or such. You'd pretty much know this was the problem.

I do not know your friend. I do not know where he works, how he tests. But an Advance Auto Parts will test it, in the car, for free, and do it in various ways, and get you a print out. I'm sure other places will do so as well. Use them.

HOWEVER... this is an oddity. There is *no way* that I know of short of a bad short that will cause a voltage drop of such magnatude that the car dies, unless the battery is also dead. This is my actual guess: the battery is borderline, and it's probably caused the Alt to die too, OR there is a short caused by a shift when accelerating.

That being said, it'll be the spare tire's low on air or something weird like that.

Last edited by houtex; Feb 29, 2012 at 09:34 PM.
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Old Feb 29, 2012 | 11:28 PM
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Originally Posted by houtex
The belt *could* be slipping. But you'd also notice the power steering sucked and your A/C wasn't working, if not hear a squeal as it stopped working.

The tensioner *could* be broken... you would have noticed that as either a snapped belt (overtensioning) or a thrown belt (the tensioner is way-loose and it throws the belt. Also noise, or jumping about or such. You'd pretty much know this was the problem.

I do not know your friend. I do not know where he works, how he tests. But an Advance Auto Parts will test it, in the car, for free, and do it in various ways, and get you a print out. I'm sure other places will do so as well. Use them.

HOWEVER... this is an oddity. There is *no way* that I know of short of a bad short that will cause a voltage drop of such magnatude that the car dies, unless the battery is also dead. This is my actual guess: the battery is borderline, and it's probably caused the Alt to die too, OR there is a short caused by a shift when accelerating.

That being said, it'll be the spare tire's low on air or something weird like that.
Yeah it's really weird if it idles its fine as soon as I accelerate the voltage goes down and after about 5 mins it starts to die. I was told it could e the tensioner but I have not had a belt snapped or thrown. I'm gonna replace all three tensioner, belt and alternator and if that does not work I suppose I'll check my tire pressure hah.

Thanks for the reply.
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Old Mar 1, 2012 | 03:08 PM
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charge the battery up and take the car somewhere to have it tested. Autozone or advance as stated above. The alt could be bad if it is acting like you stated. I have had a bed one that acted like that if I remember correctly.
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Old Mar 1, 2012 | 04:08 PM
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Its alternator.... your spinning the alternator too fast for the brushes to stay in contact with the stator. Either replace the alternator or... take it apart and replace the brushes and springs.
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Old Mar 1, 2012 | 10:58 PM
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Thanks I'm going to replace the alternator and see of that is the problem.
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Old Mar 1, 2012 | 11:09 PM
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If the car has a 3" crank pulley, replace it for at least a 4" and I would just use the original. What you gain(charging system) is more valuable than what you gain... in racing.

Also have your battery tested to see that it's capable of properly holding a charge.
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Old Mar 4, 2012 | 10:44 PM
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I changed the alternator and belt and works fine now. So must of been something inside te alternator because it tested fine.
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Old Mar 5, 2012 | 06:19 AM
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Originally Posted by 92grnmonster
I changed the alternator and belt and works fine now. So must of been something inside te alternator because it tested fine.
Told you
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Old Mar 5, 2012 | 02:27 PM
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fer shore
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