Fuel Gauge Stuck on Full

[santa6]

I have a 1988 Lund Tyee 5.5 with I/O. It has a 27gal tank under the floor.

With key off fuel gauge shows empty. Key on it goes to full regardless of fuel level.

Sending unit or gauge?

Thanks for any help.

 

[benninj]

Re: Fuel Gauge Stuck on Full

I would lean toward the sending unit. The float on the sending unit inside of the tank may be stuck in the full position and when power is sent to the gauge and unit when the key is on it is pegging out. Then with no power it defaults back to empty. Could also be a short between the hot and ground wires on the sending unit. If the circuit is closed from the wire on the center of the unit and the ground attached to base it will cause it to show full all of the time.

 

[generator12]

Re: Fuel Gauge Stuck on Full

Santa, almost always the sending unit. The gauge is just an ammeter - normally it works right or not at all. The sending unit is a variable resistor positioned by a float. As mentioned above, it may be the wiring as well, but the sending unit is typically the problem.

 

[Silvertip]

Re: Fuel Gauge Stuck on Full

Pull the sender and check the threaded terminal where it passes through the flange. Under that metal flange you will find a metal tab that eventually leads down to the potentiometer. Some folks tend to crank on the threaded threaded terminal when the install the wire and nut and that turns the stud so the metal tab touches the bracket that supports everything. That creates a ground for the "S" wire and the gauge reads full. Here is a picture. #1 is the insulator bushing that separates the threaded stud from the metal shell. #2 is the bottom of the stud to which the metal tab #3 is connected. #4 is the metal support for the sender parts. Note that #3 has been twisted to the point where it is touching #4 hence the short and hence the full scale reading on the gauge. This may not be your problem but it is one that is often overlooked.