Anybody have any knowladge on the 1990 f350 diesel fuel gage and sending units? My truck I can fill it up and the fuel guage just goes to 3/4 of a tank and stays there, does anybody know how to fix this? Im gettin aggervated with cleaning a flexable rod and guaging the fuel level. Is there any fix for this anything at all?

 

Does the gauge move at all. If the gauge jumps from empty to full and full to empty with no in-between then it is most likely the sending unit. There are several ways to test it, the best way to test the fuel gauge is at the fuel pump connector ( that way it test the wiring and the gauge) and usually it is easier to get to the fuel pump connector than getting to the fuel gauge its self. You will need a potentiometer or an old sending unit, you can usually get a potentiometer from any electronics store. All a potentiometer does it let you control the amount of voltage going through it. You will have to make jumper wires and wire it into your fuel gauge wiring then have someone watch the gauge as you slowly spin the potentiometer. The fuel gauge should move smoothly, If it doesn't then you will have to remove the gauge and test it to make sure its the gauge and not the wiring. If the gauge works correctly then its the sending unit. You can also check with it still in the truck, you will need a couple of 5 gallon cans of fuel and a Digital Volt Meter (Fluke Meter). Disconnect the fuel pump connector use some jumper wires and connect the volt meter to the fuel sending wires. Put the volt meter on Ohms and place it where you can see it while pouring the fuel in the tank. The resistance should change smoothly. If at any time it jumps or shows open then the sending unit needs replaced. I was hoping to give you wire colors and locations but I don't have that schematic, you may be able to gain them from a ford dealer or any shop that has Mitchel on demand. Good luck, hope this helps.