Problem with fuel gauge

[dwayne]

I have reviewed the online tech pages, but have been unable to solve my issue. I have a 72 Ford F100. When the tank is empty, the gauge only goes down to 1/2 full. I have removed the sending unit and cleaned the internal sweeps, wires and tab. When the tank is full, the gauge shows full, but as the tank gets empty, it will not go lower than 1/2 full on gauge. Should I try to bend the sweep and tab back slightly or is there something else I should try short of replacing the sending unit ?

[Thunderfoot]

To determine if it is the sending unit or something else, unhook the wire on the sending unit and then see what the gauge reads (be sure the wire doesn't ground on anything as this will give you a false reading). If the gauge doesn't read empty with the wire unhooked then you need to adjust the IPVR (instrument panel voltage regulator) as it is sending out to much voltage. http://www.fordification.com/fuel-sending-units.htm or you have a bad connection on the back of the instrument panel to the gauge causing some added resistance.
Do your Temp and Oil Pressure gauge (if you have them) read high?

If the gauge does read empty with the wire unhooked then there is a couple of possibilities.
1. The sending unit is bad. If you have an ohm meter you can pull it out and test it. With the arm at the top (full) it should be a short to ground, with the arm at the bottom (empty) it should be open (no connection to ground)
2. Someone replace the sending unit sometime with one that is not the right resistance value to be correct with the gauge. You might be able to put a resister in the wire to compensate for this.
3. The arm on the float has been bent and it is hitting the bottom of the tank before getting to the bottom of the travel.

I would lead more to #1 here myself but let us know how that goes and if you have any questions.

[dwayne]

I tested the gauge as per tech guide. The gauge goes to empty once you removes wires from it. The gauge shows full even if the tank 1/2 or 2/3 full. I removed the sending unit and the arm is wmoving freely. In the down/empty position, it still registers 1/2 full at the very lowest. Should I try bending the sweep back on the inside of the sending unit or should I buy a new $50 sending unit from LMC ?

[Jake11]

Replace the "constant voltage" regulator .

[dwayne]

Where is that located at ?

[seattle67]

jake11 is referring to the "IPVR". The link in Thunderfoot's post shows what it looks like and where it's located. It has an adjustment screw, I would play with the adjustment before replacing it. Though, from your description, I think the sending unit is the culprit.

[Thunderfoot]

Should I try bending the sweep back on the inside of the sending unit or should I buy a new $50 sending unit from LMC ?

It won’t hurt to try that as it isn’t working correctly now, but from everything you have done and tested and the results you got, I think it is just the sending unit itself is bad.

If you do find out something different let us know.

[seattle67]

Could always try a junk yard.