Fuel reading. My Ford e150 1978 shows tank half empty after 30 miles and 1/4 full after 50. Had tank-mounted unit replaced without any change in faulty reading. What is wrong and how to check?

 

!. Are any of the other gauges providing incorrect readings?
2. When a fuel gauge sending unit is installed it must be installed to allow the float to go to the extreme low and upper positions. If installed in the wrong position it can limit float movement and provide incorrect readings.
3. The best way to check fuel gauge operation is to lower the tank, remove the sending unit, then connect the wire from the dash gauge and ground then watch the gauge reading (key on) as the float is raised and lowered. Operation should be smooth. Float all the way down = empty-----all the way up = full.

Problem could include incorrect voltage supplied to dash gauge , incorrect sending unit for intended vehicle.

 

1. No other gauges faulty.
2. Fuel meter/sending unit has already been replaced, with no change in reading.

 

There was a voltage regulator in the dash panel that provided power to the dash gauges.
If only the fuel gauge is affected , you can verify the integrity of the wiring by just grounding the wire that went to the center of the tank unit.
It should go to the full mark , with the key on when you ground that wire that , goes to the fuel gauge.

What was the reason you replaced the tank unit in the first place?