Low Pressure Fuel System - F-150: Notes
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Fuel is pumped from the fuel tank to the primary fuel filter by the electric fuel pump. Pressurized and filtered, approximately 379 kPa (55 psi) during engine idle, the fuel is pumped through the fuel supply line to the secondary fuel filter (the secondary fuel filter is located on the back side of the engine). The filtered fuel leaves the secondary fuel filter and flows to the high pressure pump. Fuel bled off by the high pressure pump and fuel rails returns to the fuel tank. Fuel bled off by the fuel injectors is recycled to the inlet side of the secondary fuel filter.