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OT: 94 GMC elec. problem

R

Ron in AR

Member
Okay folks, here's the facts.... 1994 GMC 3500 gas, ex Uhaul truck. Been a good truck up till the last couple of weeks. Lately the speedometer goes wacky, jumps around all over the place even when I'm sitting still. Truck runs very rough. Whenever the speedometer drops to "0" regardless of actual speed, it can hardly pull itself on level ground. Backfires, misses, sometimes cuts out entirely for several seconds then fires with a bang. When the speedometer pegs on the high end regardless of actual speed, it runs much better but not great. So, anybody have any ideas of where to start looking for this gremlin?
 
I would go over all the ground connections,under the dash,and in the engine bay.
other possibillity is the ignition switch going funky( located on the steering collum,not same as key switch).
Test the batterys,and clean all batt cable connections.
Bad grounds can cause all kinds of funny things.
 
Battery is only a few months old. Heavy duty battery and the cables are in good condition. One of the first things I checked. Thanks
 
Do you mean the one at the transmission? Or is there another one? I'm an old school backyard mechanic and just don't know enough about all the electronics on the newer stuff. Thanks.
 
Hadn't thought about the ignition switch. I'll look into that. Did check all the connections everywhere I could find. Really need to get this truck going right. I use it for ranch use almost every day.
 
Don't know for sure about a GMC but I had a 90's model F350 that had a speed sensor on top of the rear end pumkin. When that went bad the speed-o-meter would jump all around and the trans shifted sh!tee.
 
That I haven't done yet. The SES light hasn't come on so I assumed it isn't something the computer can understand. But I will have it checked Monday if I don't figure out the problem today. Thanks
 
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