An in-tank electric fuel pump delivers fuel to injector(s) through an in-line fuel filter. The pump is designed to supply fuel pressure in excess of vehicle requirements. The pressure relief valve in the fuel pump controls maximum fuel pump pressure.
On Central Sequential Port Injection (CSI) systems, pressure regulator is mounted to fuel metering body under upper intake manifold. Regulator keeps fuel available to injector(s) at a constant pressure. Excess fuel is returned to fuel tank through pressure regulator return line.
When ignition switch is turned to ON position, PCM/VCM turns on electric fuel pump by energizing fuel pump relay. PCM/VCM keeps pump on if engine is running or cranking (PCM/VCM is receiving reference pulses from ignition module). If there are no reference pulses, PCM/VCM turns pump off within 2 seconds after ignition is turned on.
Most models also include a second control path through the oil pressure switch which will turn the fuel pump on after the switch detects oil pressure. Cranking time will be longer if fuel pump does not receive current until oil pressure switch contacts close.