Fuel Gauge sending unit????

I have what i think is a bad sending unit. My gauge quit working and it was stuck on E and then i hit the top of the tank and it jumped up to 1/4. So yesterday i took all the wires loose and cleaned the connections, while it was off i touched the side wire to the center and the gauge jumped up to full, but when it is all hooked up it still reads 1/4 and wont move. Do I need a new sending unit? is there any way to tell how deep the tank is without pulling sending unit? it has foam all around it so i cant even see the sides much less how deep it is. It is a 70 gallon aluminum tank in the floor of a 96 220 cuddy fish proline. any suggestions?????

Re: Fuel Gauge sending unit????

no ideas????

Re: Fuel Gauge sending unit????

if your gauge pegged to full when you touched the sender wire to ground, then yes, your sending unit is bad. That means your gauge is good

Re: Fuel Gauge sending unit????

That test does not automatically mean a bad sender. The float arm for the sender may simply be hung up on an internal baffle or touching the side of the tank. Remove the sender from the tank. Using an ohm meter, measure the resistance. With the arm up (as in full tank), it should measure about 33 ohms. Down (empty) it should measure about 240 ohms. At the half way point it should measure around 100 ohms. Don't raise or lower the lever all the way because the internal wiper may run off the resistor resulting in a false "open circuit" reading. As long as the sender varies between 33 and 240 ohms its ok. Remove the float and make sure it floats in gasoline. Sometimes they get saturated and don't float.