Fuel Pump
Fuel is supplied to the system from an in-tank positive displacement roller vane pump. The pump supplies fuel through the in-line fuel filter to the fuel rail assembly. The pump is removed for service along with the fuel gauge sending unit. Once removed from the tank, the pump and sending unit are serviced separately.
Fuel pressure is achieved by rotation of the armature driving roller vane components. The impeller at the inlet end serves as a vapor separator and a prechange for the roller vane assembly. The unit operates at approximately 3500 RPM.
The pressure relief valve in the fuel pump will control fuel pump to 60-90 psi (2.1-6.3 kg/cm2 ) maximum pressure. The fuel pump delivers more fuel than the engine can consume even under the most extreme conditions. Excess fuel flows through the pressure regulator and back to the tank via the return line.
The constant flow of fuel means that the fuel system is always supplied with cool fuel, thereby preventing the formation of fuel vapor bubbles. When the key is first turned on without the pump running, the ECM will turn the fuel pump relay on for 2 seconds. This builds up the fuel pressure quickly. If the engine is not started within 2 seconds, the ECM will shut the fuel pump off and wait until the engine starts.
As soon as the engine is cranked, the ECM will turn the relay on and run the fuel pump. As a back-up system to the 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 the 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 the engine is cold. See Fig 1 .