19-Gal Midship & 18.2-Gal Rear Fuel Tanks & FDM Pumps

To give the F-150 over 37 gallons of highway range, Ford mounted a 19.0-gallon midship steel tank alongside the frame rail ahead of the rear axle and an 18.2-gallon aft-axle tank between the rear frame rails behind the differential—each containing an integrated in-tank Fuel Delivery Module (FDM) with a high-pressure turbine pump, supply/return shuttle valves, float sender, filler neck, and stainless frame lines.

How Dual Tanks Switch Without a Frame Valve: Earlier 1980s dual-tank trucks used a complex 6-port mechanical selector valve on the frame rail that could stick and cross-fill tanks. On the 1990–1996 F-150, both tanks tee directly into a shared supply line and shared return line! Each in-tank FDM module contains an internal spring-loaded supply check valve and a pressure-operated return shuttle valve: whichever tank pump receives 12V power from the dash selector switch opens its own check and return valves with 55 psi fuel pressure, while pressure holds the idle tank’s valves tightly shut.