Fuel Pump Relay: Description and Operation

The electrical system has a fuel pump control relay controlled by the Electronic Engine Control (EEC) module, which provides power to the fuel pump. When the ignition switch is in the OFF position, the contacts of the EEC power and fuel pump relays are open.

When the ignition switch is first turned to the ON position, the EEC power relay is energized, closing its contacts. Power is provided to both the fuel pump relay and a timing device in the EEC module.

The fuel pump power supply runs through the contacts of the fuel pump relay and the inertia switch. If the inertia switch is tripped, the contacts of the switch are opened and no power will be supplied to the pump. If the ignition switch is not turned to the START position, the timing device in the EEC module will open the ground circuit after approximately one second. Opening the ground circuit de-energizes the fuel pump relay, 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 EEC module operates the fuel pump relay to provide fuel for starting the engine while cranking.

After the engine starts, the ignition switch is returned to the ON position and power to the fuel pump is again supplied through the fuel pump relay and the inertia switch. The EEC module senses engine speed and shuts OFF the fuel pump relay when the engine stops, or is below 120 rpm. The fuel pump will also be shut OFF if the inertia switch is tripped.