I am having issues with alternators. After i did my motor swap i noticed the volts were dropping from 14 down to as low as 11.8 when the motor would reach higher rpms say 5000 to 6200. So i thought it was a bad alt. so i got a different one(using 145amp by the way). No change. So i tried another thinking the one i just put on was bad. No change. So my dad has a 01 gmc sierra c3 so i tried his alt-PROBLEM SOLVED!!! I order the same alt that he has put it on and the problem returned. My main concern is that the afr goes lean like to 13.5 vs 11.2 with my dads alt. I would steal my dads but he will have the same problem then. Anyone run into this problem before? Help please.

 

i doubt the alt has anything to do with going lean. unless your voltage is dropping tremendously which i still dont see happening at higher rpms with the alt actually making more amperage.

is your alt charging fine?

in your sig it says your running 1 size bigger pulley? is this the alt? that could be your snawer, under driving the alt can cause it to not charge especially at idle.

 

have you checked all your grounds???? even if you have, i would check them again just to be sure. have you tried your alternator on your dads ride? then if that dont work steal your dads and let him deal with the problem j/k

 

I did have a larger alt pulley now but it made no diff so i took it off but i do have a larger crank pulley so i am not sure what affect that has on it. Does it need a smaller or a larger alt pulley to make up for the diff crank pulley? It is running at 13.9 to 14.1 volts at idle no matter what alt is on it. I did put my alt on my dads at it loses volts just like mine but both trucks are fine with his alt.

 

Probably not a ground if my dads alt works ok on my truck

 

Could the belt be slipping at higher RPM's? Maybe you need a shorter belt or a new tensioner?

 

I thought it might be the belt slipping but never really checked it. I thought if the belt was slipping my boost level would be dropping like the volts but its not so i am not sure on the belt. Besides how can it be the belt if the alt off my dads truck works fine. i just need the same alt on his truck but u cant get the same one from chevrolet as far as i can tell so far.