99 Jimmy: Alternator Replacement

[Ivano C]

Hey everyone,
I just installed a new alternator in my Jimmy as the other original one was bad. The truck seems to run fine but at idle the volt gauge sways quite a bit and sometimes drops well below the "14" mark on the gauge...causing the lights to dim....not sure if this is normal or if the new alt is screwed too? I have heard that GM's run funny when the battery is disconected and the computer needs to relearn the engine pattern???? Any truth to this?
I really dont want to do the alternator replacement again...any help much appreciated.

[BlazerLT]

Fisrt when it was doing this, did you have the heater control to defrost?

Also, take a voltameter out and take a volt reading off of the battery when the truck is not running and another when it is and come back with the results for me.

[Ivano C]

Blazer LT,
I did not have the heater setting to defrost...no accesories are on.....only the headlights.

The volts with the engine off are 12.8 and when running...it cycles from 14.0 to 14.8...hope this helps....thanks

[rlith]

Ivano, a slight drop is normal at idle....12.8 is aceptable. When you step on the gas it will jump to 14.00. Now if the guage were flipping all over the place constantly then there is a short somewhere. But from your description everything is fine.

[BlazerLT]

12.8 is what he read with the engine off and if it was that when he was running it would mean a defective alternator.

Althernators put out 14.4 volts appox at all time not just when you hit the throttle.

[jugstah]

Originally Posted by BlazerLT

12.8 is what he read with the engine off and if it was that when he was running it would mean a defective alternator.

Althernators put out 14.4 volts appox at all time not just when you hit the throttle.

A brand new "defective" alternator wouldn't surprise me, I've had that happen to me 2x both on a jimmy and on a ford mustang.