Fuel Pump Relay: Description and Operation

When the ignition switch is turned to the ON position, the Electronic Engine Control (EEC) power relay is energized and provides power to both the fuel pump relay and a timing device in the EEC processor. Fuel pump power is provided through through the contacts of the fuel pump relay and the inertia switch. If the ignition switch is not turned to the START position within approximately one second, the timing device in the EEC processor will open the ground circuit to the fuel pump relay. Opening the ground circuit de-energizes the fuel pump relay (opening its contacts), which de-energizes the fuel pumps.
When the ignition switch is turned to the START position, the EEC processor energizes the fuel pump relay to provide fuel while cranking.
After the engine starts, the ignition switch is returned to the ON position, and power to the fuel pump is supplied through the fuel pump relay. The EEC processor senses speed and shuts off the fuel pump by opening the ground circuit to the fuel pump relay if the engine stops or engine speed drops 120 rpm.