1992 GMC Suburban

[mrocketscience]

Hey I just picked up a nice GMC Suburban 1500. 4x4 w/350 engine. While getting the A/C serviced I noticed the alternator gauge started to bounce around and generally start reading low( Like 9v or so). After the A/C was all done I drove off and the truck just started running really badly, sputtering, no power, ect. I managed to get it home and put a voltmeter across the battery to see what was up, and it read about 21 volts. I shut off the truck and checked again and got 17 volts on the battery. Obviously the regulator is bad and I need to change the alternator. But I don't think that would cause it to run badly would it? Could the excess voltage have damaged something else? Ignition module? Computer? Just looking for some opinions from someone with knowledge about this vehicle.. Thanks.

[Deaf Bob]

Weak battery will make the motor die..
I know running 2-12 volt batteries as 24 kills the modules.. But run rough... Not sure..

[Barry Donovan]

still got the old lights I see..
huge amperage waiting to be used... they stay primed lights on or off.
even the next generation up, the 1996.

the simple stuff..check under battery, see if it is munched into the steel tray yet.
the tail lamps have a bad circuit board..but if you keep a fuel pump, they must still be ok.
see if it has an electric trailer brake gadget. throw it back at asia, via the ocean.

the biggest monster to me was the light circuit. 40 something amps just for parking. Crazy.

all else is so simple, not even a hot rod editor could have a real complaint.

the blippy end to an alternator.. its got tungsten written all over it.

the gmc has a unique blinker pattern up front... this makes it a hog for reasons unknown.
LED conquered it, very nice idea they had there. As if there is no negative... one light switches to another. Two different blinks for one blinker.

[tardis454]

Plop an alternator in and see what it happens. The fuseable links in the wiring harness 'should' catch a voltage spike.
If it's discharging, low voltage while driving, overcharging at idle, and overcharged turned off then the regulator is toast.
You might wanna do a load test on the battery too while you're in there, it doesn't hurt..

[mrocketscience]

Just an update... It seems the alternator is fine, my voltmeter was reading faulty. Put a new battery in the voltmeter and it's reading normal. Doh. So, the problem turned out to be:

Plugged fuel filter
Bad Ignition module
Plugged catalytic converter
performed tune up (plugs, wires, cap, coil)

Seems to run like a champ now, drove it to work today in L.A. traffic as a sort of stress test and it ran fine. Yay!

[Loren]

Just to add something of a similar story, the 350 truck I had for a few years suddenly started to run horribly after a thermostat change...it would run good, then could barely move. That truck had so many problems it was killing me but this time it was my fault...I forgot to tighten the ground wires at the thermostat housing and that's all it took to start acting like it lost it's mind.