Fuel Pump Relay: Description and Operation

DESCRIPTION

^ Has a fuel pump relay controlled by the Powertrain Control Module (PCM), which provides power to the fuel pump through an inertia fuel shutoff switch, which is normally closed.

^ Dependant upon the operating conditions, the power current path to the fuel pump is provided through two relays:

- High speed fuel pump relay.

- Electronic Engine Control (EEC) power relay signal from the Variable Control Relay Module (VCRM).

OPERATION

The fuel pump electrical supply will be at system voltage during starting and high fuel demands. At other times, voltage will be reduced.

^ When the ignition switch is in the OFF position:

- The contacts of both relays are OPEN.

^ When the ignition switch if first turned to the RUN position:

- The EEC power relay is energized, closing its contacts.

- Power is provided to both the fuel pump relay and to a timing device in the PCM.

- The fuel pump runs through the contacts of the fuel pump relay.

^ If the ignition switch is not turned to the START position:

- The timing device in the powertrain control module will open the ground circuit, after approximately one second. Opening the ground circuit de-energizes the fuel pump relay, opening its contacts, which in turn de-energizes the fuel pump. This circuitry provides for pre-pressurization of the fuel system.

^ When the ignition switch is turned to the START position:

- The PCM operates the fuel pump relay to provide fuel while cranking.

^ After the engine starts and the ignition switch is returned to the RUN position:

- Power to the fuel pump is again supplied through the fuel pump relay.

- The powertrain control module senses engine speed and shuts off the fuel pump by opening the ground circuit to the fuel pump relay when the engine stops or is below 120 rpm.