The Stovebolt Site Forums The Shop Area General Truck Talk Fuel Sending Unit

The fuel guage in my 66 still isnt working. So far, I have replaced all the wiring from the fuse panel to the sending unit and the fuel guage in the dash. Dad and I removed the sending unit (we replaced it 2 years ago). The guage works with the sending unit out of the tank and goes through the full sweep, but when the sending unit is in the tank, it reads empty, regardless of the fuel level. I'm thinking that the sending unit has gone south for the winter. What do you guys think?

[QUOTE] [The guage works with the sending unit out of the tank and goes through the full sweep, but when the sending unit is in the tank, it reads empty, regardless of the fuel level.]

If the needle moves when you move the arm back and forth then the sending unit is functioning. Sounds to me like you have a hole in the float. Gently remove the float from the arm and see if it bubbles when you hold it under water. You can buy the float separately.

Curt B.

66stepside,

I will assume your truck has only the 'in cab' fuel tank and no other tank. The schematic shows two tanks were available.

When you pulled the sending unit and tested it and the gauge, it worked...how were you grounding the sending unit during this test.

The resistance of the sending unit must be matched to the gauge. AD rigs historically used 30 ohm units...did the newer rigs switch to 90 ohm along with the rest of the industry? These components have to match.

Something is wrong with your troubleshooting. If the gauge worked when the sender was pulled and manipulated manually, it HAD to be grounded somehow, and this test showed that the gauge responded to the sender...it worked.

Unless the wiper on the arm isn't making contact when the unit is stuffed back into the tank and causing this problem, then something is rotten in Salisbury!

Have you done this simple little test yet? Key on, pull wire from sender, gauge should read FULL.

Key on, ground wire (known, good ground), gauge should read empty.

The sender must be grounded, either through the tank, or with its own wire. The fuel gauge should be grounded too...probably through its case, but it must be grounded.

When the sending unit is in the tank and the gauge is hooked to it, it would read EMPTY if the sender was shorted to ground, or the float sank!

Keep looking and keep us posted. Things like this get more exposure in the electrical forum.

Stuart

Has the sending unit you replaced two years ago been in service and working OK since? It just recently stopped working? Or did you buy it two years ago and just got around to installing it? The reason I make that distinction is the new sending unit I used for a while on my 38 was so stiff that the float wouldn't raise the lever. I had to add a second float to get it to work. After it got "broken in" it worked OK with one float. Just a thought.

Automarc, I have the in-cab tank. I replaced the ground wire that goes from the sending unit to the cab and the wire that goes from the sending unit to the fuse panel. when I remove either wire, the guage reads full and when i touch either wire to the other, it immediately goes to empty. I mentioned to my dad that I suspected the wiper on the arm not making contact when it was immersed in gas since it worked out of the tank and everything was dry. He said to check the float in the tank, then go for the sending unit itself.

Tiny, I installed it two years ago when the original one crapped out. Its worked fine up until about a month ago. I replaced the guage itself and that didnt solve the problem.

66stepside,

Your test methods indicate the wires are intact and the gauge is working perfectly. The problem must be your sending unit...or your float has sprung a leak!

Stuart