Bad Alternator???

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  #1  
Old 04-23-11, 01:04 PM
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Bad Alternator???

I have a 96 Chevy Blazer I am having problems with. Car runs fine when nothing electrical is turned on. However, when I'm setting at an idle if I turn the headlights on or the heater on or even whenever I hit the brakes the voltmete will jump from 14 to about 12 and fluctuate between 12 and 14. While doing thes the car feels like its going to stall. It does the same thing while not at an idle but not nearly as bad. I took my blazer to advance auto parts to have them check the alternator and they claim it is fine. One thing I ended up doing is I started the car and disconnected the positive terminal to the battery and the car ran just fine. But as soon as I turned the headlights on the car turned off. By the way the battery ios brand new so i know theres no problems there. Does this sound like a bad alternator or voltage regulator? Any help would be great. Thanks.
 
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  #2  
Old 04-23-11, 03:48 PM
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You might try another store and have them check out your charging system. I would suspect the alternator isn't putting out enough to keep up with the load. It would also be a good idea to check your electrical connections to make sure they are clean and getting good contact.
 
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Old 04-23-11, 06:43 PM
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Pulling a batt cable on a running vehicle was a barnyard way of checking a GENERATOR. Do not do this on alt equipped vehicles they have delicate electronics that can be damaged from the surge when there is no batt for the current to go to. Next time you have it checked turn on several items and see if it keeps up. How is your belt and idlers?
 
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Old 04-23-11, 07:40 PM
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Check all your ground and battery connections to make sure they are clean and tight, at the battery and alternator. How do the cables appear? If in doubt, replace. Do you have the side terminals? Double check them.

Put a real voltmeter on it and tell us what you get at idle and at about 1500 rpm. Don't rely on the gauge.

The regulator used to be in the alternator for GM's.

Like wrench says, don't pull a battery cable on an alternator equipped car, you're begging for trouble.
 
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Old 04-23-11, 09:28 PM
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The regulator used to be in the alternator for GM's.
They still are. My 96 s 10 had the same issues. It was the regulator inside the alternator. Thats why they are so darn expensive. $200 bucks for a reman no less.

Mike NJ
 
  #6  
Old 04-24-11, 05:20 PM
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Originally Posted by retired wrench View Post
Pulling a batt cable on a running vehicle was a barnyard way of checking a GENERATOR. Do not do this on alt equipped vehicles they have delicate electronics that can be damaged from the surge when there is no batt for the current to go to. Next time you have it checked turn on several items and see if it keeps up. How is your belt and idlers?
uhhhh we put surge protective zeners in these cars. Your alternator has a voltage regulator. It needs to know what 0Volts is. This is done through the ground circuit. you need to have a good ground from the engine to the chassis. in this old of a car it probably coroded to a higher resistance. Which i model as part of the circuit. Run a wire from the alternator to the battery ground and i bet you your issue is gone. cuz you have a bad ground which this truck is known for which causes low charging voltage cuz the ground will float when it corrodes.
 
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