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What are the signs of a bad alternator?

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Old Jul 12, 2005 | 12:56 PM
  #1  
Tripper511's Avatar
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From: Long Island NY
Car: 1982 Trans Am
Engine: 350 4BBL
Transmission: 4 Speed Manual
Axle/Gears: 3.23
What are the signs of a bad alternator?

I think my alternators gone bad. I just installed a new cd player in my car and now when ever I start the car it struggles or sometimes doesn't even start at all (last thing I need in this heat). I dont think the cd player is hooked up wrong because there's only one wire for positve and one for negative (pretty much fool proof). So all I can guess is that the alternator isn't sufficently charging my battery. Any thoughts on that?
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Old Jul 12, 2005 | 08:09 PM
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EmoDork138's Avatar
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From: Michigan
Car: 88 Trans Am GTA
Engine: 5.0 TPI
Transmission: T5
Reading your post i have a few thoughts that you may want to explore... hopefully they help.

Personally i wouldn't think this is an alternator problem. Typically when an alternator goes.. they just go. And you as a driver end up on the side of the road w/ 0% battery in your car.

What you may have a problem with here is a battery problem. You may have a bad battery. How new is it? Also you may want to check your positive and negative wires and how they connect to the battery itself. If you have a bad connection between them (if by chance they are corroded (sp) or if you accidently crossed threaded them when you connected up your radio, then your car will struggled to draw juice from the battery when you start the car). Also check and make sure your battery has water in it. Im really not sure if this would do anything, but hey its easy enough to check.

And another way to check to see if your not getting enough charge from your alternator, is to drive around w/o your radio for a few days. Does this change anything? If your problem goes away, then you may be right.

Goodluck!
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Old Jul 12, 2005 | 10:03 PM
  #3  
comm's Avatar
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From: Oklahoma City
Car: 1984 z28
Engine: 305
Transmission: 700r4
When my alternator went bad my choke light would come on, usually accompanied by a weak buzzing sound, when the engine was at a lower RPM. I believe the way the choke light is wired in a way in which it also serves as a charging system warning light. I think this would also apply to your car, mine is a 1984.
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Old Jul 13, 2005 | 09:27 AM
  #4  
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Car: Which one?
Engine: 355
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Signs of a bad alternator are excessively high/low/no voltage output, and a large decrease in output voltage when accessories are turned on.

I only know one style of GM alternator, and all it takes to test is a multimeter. One wire to ground, one to the terminal lug on the back of the alternator. If it's below about 13V at idle, with no accessories on, the regulator is likely on it's way out.

I've had one fail, and the gauge showed the steadily declining voltage of my system.

Another one, the voltage dropped (around 12V) when just the heater or headlights were turned on, which dimmed all the lights. Pulled the alternator out, $20 rebuild kit later, 14V at idle, problem gone.
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Old Jul 13, 2005 | 10:20 AM
  #5  
Tripper511's Avatar
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From: Long Island NY
Car: 1982 Trans Am
Engine: 350 4BBL
Transmission: 4 Speed Manual
Axle/Gears: 3.23
Originally posted by EmoDork138
(if by chance they are corroded (sp) or if you accidently crossed threaded them when you connected up your radio
cross threaded, what does that mean exactly? Can you elaborate on that.
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Old Jul 14, 2005 | 02:07 AM
  #6  
EmoDork138's Avatar
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From: Michigan
Car: 88 Trans Am GTA
Engine: 5.0 TPI
Transmission: T5
I mean, if you didn't properly screw in your positive wire's nut into the battery pole - they can make a poor connection and may cause your problem
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Old Jul 14, 2005 | 04:40 AM
  #7  
Difflock's Avatar
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From: Lancashire County, England, UK
Car: VIN=85 T/A, CAR=82/3 T/A gfx, go figure. She's a T/A anyway!
Engine: 5.0, Holley 600 cfm 4-barrel
Transmission: THM350 ??
Yes, you think you've screwed the nut up tight when in actuality it's binding on the threads. Worst case is you can strip the threads so it won't tighten at all

Hey, Comm thanks for that info - it's exactly what happened re: my choke light too! When my alternator went bad - there was a brief period of excess volts followed by 12V - the system JUST about held its own.

Mark.
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Old Jul 14, 2005 | 04:27 PM
  #8  
RebelGQ's Avatar
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From: POMONA, CA
Car: 91 Camaro Z28
Engine: V8 5.0L
Transmission: auto
Originally posted by dyeager535
Signs of a bad alternator are excessively high/low/no voltage output, and a large decrease in output voltage when accessories are turned on.

I only know one style of GM alternator, and all it takes to test is a multimeter. One wire to ground, one to the terminal lug on the back of the alternator. If it's below about 13V at idle, with no accessories on, the regulator is likely on it's way out.

I've had one fail, and the gauge showed the steadily declining voltage of my system.

Another one, the voltage dropped (around 12V) when just the heater or headlights were turned on, which dimmed all the lights. Pulled the alternator out, $20 rebuild kit later, 14V at idle, problem gone.
My car is experiencing some voltage drop, when im driving, it stays between 14V to 18V, but when i drive more and more, or sometimes when i start up my camaro, it'll stay between 8V and 13v, DO U THINK my regulator could be going bad, because i checked my connections, they seem connected snug and properly. my battery seems fine and the alternator could be fine, but then again, i could be wrong, any suggestions?
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Old Jul 14, 2005 | 09:09 PM
  #9  
Tripper511's Avatar
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From: Long Island NY
Car: 1982 Trans Am
Engine: 350 4BBL
Transmission: 4 Speed Manual
Axle/Gears: 3.23
I figured it out, I just needed to clean the batty connection and then reconnect it. She starts up fine now, thanks.
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