My son has a 94 f-150 with the 5.0 engine.We just bought the truck and gave had it tuned and serviced.We filled it up which took right at 16 gallons from empty.He has only put right at 90 miles on the truck and it is already at 1/8 of a tank.I dont think he is only getting roughly 6 mpg and there are no leaks etc,,is there another problem that needs looked at that could be causing this?Thanks

 

I had mine replaced, and it does not read like it used to. When mine now reads 1/8 of a tank it really means empty. Maybe my Ford dealer installed the incorrect one.

Fill it back up when it hits 1/8 of a tank, and calculate your mileage on gallons used.

 

I has a 93 Bronco that had the same problem. After I dropped the tank and pulled the sending unit, it turned out to have a pin hole in the float causing all the trouble

 

Fill it to the top until the pump clicks off.
Write down the mileage and set the odometer to 0.
Drive for 50 miles then go back to the same pump (to be totally accurate but not required) and fill up again until the pump clicks off.
Write down the amount of gas used to fill up again, and divide that into your mileage.
That will give you a true MPG.
If the MPG is way higher than what the gauge shows or it took a lot less to fill it up than the gauge shows is should, you need to replace the fuel sender in the gas tank.
If your mileage is in fact 6MPG you either have a leak or your son should be driving for NASCAR with his lead foot.
Or your brakes could be dragging, your transmission could be dragging, you could have a pressure leak in the fuel system when running, computer running too rich, oxygen sensor bad, clogged air filter, map sensor bad, etc. etc. etc.
You should be getting about 12 MPG in the city under NORMAL driving.