Fuel Gauge Pegged Past Full - HELP!

[Mikee]

I am very stressed and annoyed, so bare with me here.

I purchased my "new to me" 1980 2500 square body 4x4 a few days ago. One of its MANY issues is the fuel gauge which is always pegged way past full. It is a problem that needs to be addressed immediately.

I have tried and tried to figure out what the hell is going on.

The truck had dual tanks, but one of the tanks was removed. Previous owner told me the gauge was working fine but randomly stopped and he never figured out why. This truck has had a lot of wiring modifications done just looking underneath everything is crimped and heat shrinked and whatnot.

I need a guru. I need someone to help me get this darn gauge working again. I have a literal headache from trying to figure this out for days.

 

[Georgeb]

Was the switch in the dash and the valve removed from under the truck? Have you verified the ground to the sending unit in the tank in in tact?

 

[Mikee]

Was the switch in the dash and the valve removed from under the truck? Have you verified the ground to the sending unit in the tank in in tact?

Selector switch and valve are still on the truck. I see a ground coming down from the pump and onto the frame. Wasn't able to get it off as the bolts were seized in place.

 

[nickbailey1993]

Pegged past full is where the gauge goes when there is no signal from the sending unit. Probably a bad ground or broken wire somewhere

Sent from my Z798BL using Tapatalk

 

[marks86]

most of the time, its a bad ground.

 

[1987 GMC Jimmy]

It's very likely a bad ground. That being said, mine would start out pegged past full and weirdly go back down as the fuel level went down. The sending unit was bad in that particular case.

 

[Mikee]

Which grounds should I be checking? And where are they?

 

[Georgeb]

It would be the ground at the tank I
mentioned before. If you find a good ground point on the frame and can measure the resistance between the signal wire and that ground this will tell us if the sender or ground is an open circuit. If your ground at the tank is good and you get an ohm reading somwhere between 0 and 90 start reading that sending wire at every plug from there to the cluster. There should be one on the diverter valve.

 

[Mikee]

It would be the ground at the tank I
mentioned before. If you find a good ground point on the frame and can measure the resistance between the signal wire and that ground this will tell us if the sender or ground is an open circuit. If your ground at the tank is good and you get an ohm reading somwhere between 0 and 90 start reading that sending wire at every plug from there to the cluster. There should be one on the diverter valve.

Removed and cleaned ground connection, no dice. Still same problem. Tried jumping the two pink wires for the two sending units (video I saw where a guy did that)... no dice. Same problem. So I am stumped. I don't quite know what you mean with measuring the resistance and whatnot

 

[Georgeb]

What happens when you jump the pink wire to ground? Does the guage respond to that?

 

[Mikee]

What happens when you jump the pink wire to ground? Does the guage respond to that?

Should I take the ground off and splice the two together with the ground off, or leave the ground on the frame and splice the two together?

 

[Georgeb]

Should I take the ground off and splice the two together with the ground off, or leave the ground on the frame and splice the two together?

please explain in better detail which two you wires you are referring to, where they come from and where they go.

What we are trying to do is ground out the pink wire that runs up to the gauge. this should take the guage all the way down to empty. If it doesn't there is an issue between that point of the signal wire and the gauge. If it does the issue will be between that point and the sender or the sender itself.

 

[Mikee]

please explain in better detail which two you wires you are referring to, where they come from and where they go.

What we are trying to do is ground out the pink wire that runs up to the gauge. this should take the guage all the way down to empty. If it doesn't there is an issue between that point of the signal wire and the gauge. If it does the issue will be between that point and the sender or the sender itself.

Pink wire comes down from the pump, (then they have spliced in a different color). Then leads to the front of the truck up into the cab. Ground wire comes down from top of pump and grounds on frame close by.

 

[Georgeb]

Ground that different wire to the frame and see what the gauge does.

 

[Mikee]

Ground that different wire to the frame and see what the gauge does.

So cut that pink wire and ground to frame to test? Sorry I'm an idiot lol