Fuel Gauge Question

[1979bettywhite]

So I have an MTS poly tank in the Cherokee. It has the separate sending unit. I believe my sending unit it good. I have it grounded through one of the retainer plates that mount and hold the sending unit. Used a spot on the chassis for the other end of the grounding wire.

I am having an issue that when I have been running things for a while the gauge wants to peg out past the Full mark. When I first start the jeep up and run things it seems to be showing correct on the gauge, but after a while (jeep has warmed to operating temperature etc), the gauge will periodically peg out. It will periodically come back from time to time, but it's rather random.

I am wondering if it is a grounding issue? What causes our fuel gauges to peg out past full? I may try swapping to a new ground location and see if that changes anything.

Any thoughts?

[ShagWagon]

You can run 12v straight to the sending unit with a battery then test with a meter to check your ground. Then move backwards to the gauge, circuit board, board pins, ring plug, fuse box. Checking for dirt, corrosion, buildup etc...

[ShagWagon]

Dbldbldbl

[ShagWagon]

You can run 12v straight to the sending unit with a battery then test with a meter to check your ground. Then move backwards to the gauge, circuit board, board pins, ring plug, fuse box. Checking for dirt, corrosion, buildup etc...

Disconnect the battery first...

[PossumJr]

On these gauges, pegged at Full indicates low resistance on the sending unit circuit. If anything your ground is likely fine otherwise you would be seeing the opposite problem. Instead it sounds to me as though there is an intermittent short circuit occurring somewhere between the gauge and the sending unit, or there is something up with the sending unit itself.

[ShagWagon]

Also some thing like 85 and older(?) are different. One pegs full. One pegs empty. Can’t recall which is which lol.

[1979bettywhite]

Happened to me again this morning on my drive to work. Gauge worked fine for about 30 minutes. Then right when I got to work it pegged out to past full again. Just an odd occurrence. I am going to swap the grounding location for the sender, but this sure is odd. I hope I don't have to drop the tank again, but may not be able to avoid it. I think I have had this tank out about 4-5 times now. Becoming an old pro at it, lol. Just time consuming to drain most of the fuel out.

[67GMC]

On my '84, grounding the sending unit wire pegs the meter to full (past full). So if it works normally for a while, you probably have a short on the power side (not the ground side). A bad ground would indicate empty more than full if your Jeep works the same as mine.

[4bz]

It sounds like the resistance wire in your sending unit is not making a continuous contact with the float arm wiper. Fuel moving in the tank (on turns and bumps) while you are driving the vehicle causes the electrical signal to the gauge to randomly become open as the float moves and the wiper loses contact. This happens as sending units become worn and lose contact tension between the float arm wiper and the resistance wire. Replacing the sending unit would be the best fix. You might be able to confirm that the sending unit is the source of the problem by driving the vehicle with the tank almost
empty. If there is not enough fuel in the tank to move the sending unit float arm, the gauge will remain constant.