Fuel gauge problem

[Purplerambler69]

Hello, I recently bought an M925a1. My fuel gauge isn't reading properly. Is reads full when the tank is full, but as I use fuel it doesn't really drop. It just kind of starts bouncing around. I've had it down to about 1/2 a tank of fuel and the gauge is bouncing between 3/4 and full. Does this sound like a gauge issue or am I looking at a bad sending unit? I'm totally new to this scene but I'm guessing someone out there has dealt with this issue before. Thank you all!
Wade

 

[Floridianson]

I might check the securing clip behide the gage for a good ground first.

 

[cranetruck]

I might check the securing clip behide the gage for a good ground first.

Yes, the sending unit and gauge relies on a number of ground connections along the path to give you perfect readings, which include the fuel tank itself and the instrument panel, but you may want to start with pulling the sending unit and checking its operation.

The full and empty adjustments will be found in your TM.

 

[orren]

Yes, the sending unit and gauge relies on a number of ground connections along the path to give you perfect readings, which include the fuel tank itself and the instrument panel, but you may want to start with pulling the sending unit and checking its operation.
View attachment 453622
The full and empty adjustments will be found in your TM.

Cranetruck:

This is very helpful but do you have the same type of check for the panel fuel gauge, too?
What TM might all these things be found in?

Thanks for the help.
Orren

 

[Warthog]

Never ever trust a fuel gauge in a military truck. YMMV

 

[Purplerambler69]

Thanks for the input folks! Will check grounds asap. I think Warthog might have the best advice though!

 

[cranetruck]

Never ever trust a fuel gauge in a military truck. YMMV

I agree, but there are ways to improve the reliability. The sending unit is grounded via its mounting screws to the tank, to the fuel pump wiring and finally to the frame. To shorten this path, add a ground wire directly from the sending unit to the frame.
The instrument cluster can be wired like this,


This is from a PS magazine note,


The -20 manual should have the fuel level sending unit height adjustment info.

 

[EMD567]

What Warthog said---- Get an old axe handle, or shovel handle. Cut it off so that you have a foot or so sticking out of the tank. Find something to hold 5 gallons of diesel. Place the handle in the tank, make a mark where the fuel level is. Add 5 gallons. Make another mark, measure the distance between the two. Then go to the bottom of the handle, measure up the handle the amount that the 5 gallons raised the fuel level. Repeat, until you have 7-8 marks. Notch the marks, so that when the sharpie wears off, the marks are still there.

Now you have a mark I fuel gauge, and it will never read incorrectly, or bounce around. It doesn't need good grounds, and it works, even when the batteries are dead. Keep it with the truck at all times.

 

[steelandcanvas]

What Warthog said---- Get an old axe handle, or shovel handle. Keep it with the truck at all times.[/QUOTEused

I used an old broom stick and made Sharpie marks at 1/4, 1/2, 3/4, and Full. Drilled a hole in the end, attached a loop of 550 Paracord to hang it in the cab. It also makes a nice (tire) thumper.