Fuel Pump
Fuel is supplied to the system from 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. Once removed from tank, the pump and sending unit are serviced separately.
Fuel pressure is achieved by rotation of armature driving the roller vane components. The impeller at inlet end serves as a vapor separator and a precharge for the roller vane assembly. The unit operates at approximately 3500 RPM.
The pressure relief valve in the fuel pump will maintain fuel pump pressure at 60-90 psi (4.2-6.3 kg/cm2 ). The fuel pump delivers more fuel than the engine can consume even under the most extreme conditions. Excess fuel flows through pressure regulator and back to fuel tank through return line.
The constant flow of fuel allows fuel system to always be supplied with cool fuel, thereby preventing the formation of fuel vapor bubbles. When the ignition is first turned on without engine running, the ECM will turn on fuel pump relay for 2 seconds. This will rapidly pressurize fuel system. If the engine is not started within 2 seconds, the ECM will shut fuel pump off and wait until engine starts.
As soon as engine is cranked, the ECM will turn on relay and run the fuel pump. As a back-up system to fuel pump relay, the fuel pump can also be turned on by the oil pressure switch. The oil pressure switch is a normally open switch which closes when oil pressure reaches about 4 psi (.30 kg/cm2 ). If fuel pump relay fails, the oil pressure switch will close and run the fuel pump. An inoperative fuel pump relay can result in long cranking times, particularly if engine is cold. See Figure .