Fuel Pump
Fuel is supplied by an in-tank positive displacement roller vane fuel pump. The pump supplies fuel through the in-line fuel filter to the fuel rail assembly. The pump is removed for service along with fuel gauge sending unit. See Fig 1.
Once removed from tank, pump and sending unit are serviced separately. The pressure relief valve in the fuel pump, controls fuel pump maximum fuel pump pressure at 60-90 psi (4.2-6.3 kg/cm2 ). Excess fuel flows through pressure regulator and returns to the tank.
The constant flow of cool fuel prevents fuel vapor bubbles. When ignition is turned on, fuel pump relay activates the fuel pump for 2 seconds to prime the injectors. If engine does not start within this time, the ECM deactivates fuel pump until engine starts.
After engine starts, the ECM closes the fuel pump relay, activating the fuel pump. As a back-up system to fuel pump relay, fuel pump can also be activated by an oil pressure switch. The oil pressure switch is normally open until oil pressure reaches approximately 4 psi (.28 kg/cm2 ). If fuel pump relay fails, the oil pressure switch closes when oil pressure is obtained, operating the fuel pump. Inoperative fuel pump relay may result in extended cranking times.