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Alternator causing running issues

Old 05-16-2019, 09:40 AM
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Alternator causing running issues

Car runs fine if alternator is unplugged. Car will barely idle and will not accept much throttle when alternator is plugged in. I have a 92 camaro with an L98
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Old 05-16-2019, 10:02 AM
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Re: Alternator causing running issues

Originally Posted by McComas87 View Post
Car runs fine if alternator is unplugged. Car will barely idle and will not accept much throttle when alternator is plugged in. I have a 92 camaro with an L98
Replace the alternator. Most likely diodes going out causing AC voltage to leak into the system. Everything on the car runs off DC and AC creates havoc. Should not have more then .5 AC if you test across the battery posts and normally you will see well below that.
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Old 05-16-2019, 10:11 AM
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Re: Alternator causing running issues

I agree.
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Old 05-16-2019, 12:15 PM
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Re: Alternator causing running issues

Originally Posted by dmyruski View Post
Short version: 92 Z-28 305TPI, It will start but then stall out after 30-45 seconds or if I press the throttle. I had a battery charger hooked up and the key on when I heard a very slight Humming / ringing noise in the engine compartment. Found it was coming from the alternator. I unplugged it and she runs. Had a little hesatstion but probably needs to clean itself out. While running I plugged the alternator back in and she stalls instantly. I assume the alternator is back feeding and I think maybe messing with the fuel pump or injectors. Anyone ever have this happen or idea of what's actually happening? Is it a simple change the alternator or could there be an underlying problem.

I put a new A C Delco alternator on 3-4 years ago.
Originally Posted by OrangeBird View Post
The "humming/ringing" noise in the alternator with the battery charger hooked up to the battery is a classic telltale of shorted diodes in the alternator . An alternator , as it's name implies , generates AC power , which must then be rectified into DC power by a network of diodes in order to charge your battery and play nice with all the other DC devices in your car . The shorted diode(s)* not only allow the crude DC (unfiltered with lots of "ripple") of the battery charger to ring the stator coil(s) when the car is off and your trying to charge the battery , those same shorted diodes also put an unfiltered AC artifact on to your supposed to be pure DC system when your car is running . And in your case your ECM doesn't sound like it's appreciating running on the amount of AC your alternator is putting out , hence the car running OK when you pull the plug and stop the alternator's output .


*Could be one or more , the alternator puts out "3 Phase" AC which is rectified into DC by a set of 6 Diodes , three positive going and three negative going , usually with a final "protection" diode on better built units bringing the total to 7 .
Wow this is weird , the above two posts were only a few days ago dealing with a cur running bad from "dirty DC" (AC on the DC line) , it's a kinda rare thing generally , compared to the alternator just failing outright . Bad day at the Diode factory
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