Alternator Causing rough idle on L31 in 1974 Chevy

Discussion in 'Gasoline Engines' started by bugman40284, Apr 29, 2018.

  1. bugman40284

    bugman40284 Registered User

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    Dec 28, 2013
    Folsom CA
    So as the title reads I am having an alternator issue with my brothers truck. We put an L31 into a 1974 Chevy truck. We had the computer reprogrammed and everything seemed to be working great until we started wiring up the alternator. When the alternator is charging then the motor starts running like we just dumped a bunch of sea foam into it. It smokes and smells and idle horribly. We have tried wiring the alternator independently with a resistor and we have tried wiring it through the dash but it did not seem to make a difference. The only thing I can think of is maybe one of the sensors is getting to much voltage when the alt is plugged in. I did unplug the MAF sensor when it was charging and there was no change in the sound of the motor. We have run all of the grounds to nice clean locations and when we test the grounding it seems excellent. I am just curious if anyone has run into this problem. So my next move is to change out the MAF and see if that fixes it but I highly doubt that it would cause this issue.

    Alt: c-130
    Engine: L31 Vortec out of a 99 silverado or yukon
    trans: 4l60 or 4l80, Haven't really looked.
    Truck: 1974 purple chevy

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