Section 10-01A: Fuel Tank, Filters, Tubes and Electric Fuel Pump, Gasoline Engines | 1996 F-150, F-250, F-350, F-Super Duty and Bronco with Gasoline Engines Workshop Manual |
All vehicles are equipped with a restricted opening on the fuel tank filler pipes (9034) that allows only a non-leaded fuel nozzle to be inserted.
The fuel tank filler pipe openings for the fuel tanks (9002) on trucks with multiport fuel injection (MFI) engines (6007) have been made smaller to prevent accidental filling with other than unleaded fuel. Gasoline pumps in the United States and Canada dispensing unleaded fuel are equipped with nozzles to accommodate the smaller filler opening on the fuel tank filler pipe.
The restrictor in the fuel tank filler pipe consists of a narrow opening in the fuel tank filler pipe covered by a spring steel trap door. The smaller non-leaded fuel nozzle will fit through the narrow opening and push the trap door aside, allowing normal filling. Leaded fuel nozzles will not fit through the narrow opening. The trap door being closed causes a fuel backup and automatic nozzle shutoff.
The restricted fuel tank filler pipe is manufactured as an assembly, and must be serviced by removal and replacement with a new part. Fuel tank filler pipes are not to be modified in any way.
The fill limiting system is designed to permit an approximate 10-12 percent tank volume air space when the fuel tank is filled to capacity. This air space provides for thermal expansion of fuel as well as being an aid to the in-tank vapor vent system.
Expansion of fuel due to temperature increases or overfilling ("topping off") causes fuel overflow at the fuel tank filler cap (9030) when the vehicle is standing or the fuel tank filler cap is removed. To minimize this condition, it is recommended that the amount of fuel put in the fuel tank when filling be limited to the automatic pump shutoff. If vehicle has two fuel tanks, use fuel from both fuel tanks after fill-up to reduce fuel levels.