electrical problem

[Rocklin]

Ok so my old battery in my truck was the original battery from 2003 when it left the factory,  I changed it to a new battery and the problem soon began.  my alternator squeals and the volt gauge on the dashboard fluctuates from 15 volts to 13 volts rapidly,   when I accelerate the V8 feels "sticky" and then when im up to speed it smooths out.   when I come to a stop the lights on the dash all go dim and the RPMs drop to 400 and the Motor gets the shakes like it will stall but the governor comes on and picks it up to idle speed which on this truck seems to be 550-600 RPM.    when the lights go dim the computer informs me that the airbag system needs service.

so do you think I need a new alternator? or did I fry something by putting the new battery in,   it took a few tries to get the positive battery lead connected to the battery because its a screw in type and the space is tight.   I kept making and breaking contact when installing the positive lead and the car alarm kept going off.

[MoaningLisa]

check alternator voltage at alternator and terminals with a DVOM

are your terminals corroded at all?

did you connect the battery the wrong way at first?

[Rocklin]

my terminals are nice and clean,  I think I was the first person to ever remove them from the old battery.   I checked twice to see if it was hooked up with backwards polarity  but it's hooked up right.

[MoaningLisa]

do you have any codes?

disconnect the battery and reconnect it.

also, voltage?

[Rocklin]

no codes "yet" besides the emissions leak at the gas cap.

ill give it a try tomorrow disconnecting and reconnecting the battery.   right now someone has my voltage tester so ill have to go get it back.

[AngryOnion]

I need more info ,make model year all that shit.

[Rocklin]

I need more info ,make model year all that shit.

2003 GMC Sierra SLE stepside with the 4.8l V8.

[AngryOnion]

OK great I will run it through my data base on Monday morning and get back to you.

[Rocklin]

Well I decided to replace the alternator,  after running a few checks that's what the problem was.  $200 later and 45 minutes of work the truck runs fine besides the battery was run down (it ran off the battery for almost 2 days).

the voltage gauge on the dash that was going back and forth from like 12 volts to 14 told me that the motor was running off the alternator only part of the time and off the battery the rest of the time.

[MoaningLisa]

sounds more like the regulator than the alternator...but since its an internal regulator, it doesn't matter.

good thing you got it.

[Rocklin]

Ok the problem has returned,   its dealership time I think.


all the original problems have come back except for the alternator one,   now the airbag system is warning me all the time instead of only some of the time.  when I come to a stop the RPM's drop even further now to 250-300 and if I turn the heater on the motor stalls out briefly and then picks itself up again to 300 RPM or so.

sticking in the new alternator fixed the problem for 2 days fuck me.

[MoaningLisa]

again, it sounds like the regulator. get the PCM open on HP tuners and check all your voltage parameters. it might be a bad PCM causing this, or some setting got fucked.