Fuel Pump Relay and Inertia Switch
The Fuel Pump Relay is a normally open contact relay used to control the fuel pump. The relay gets its B+ feed from the ignition switch through fuse 20 and is energized when the EMS2000 provides a ground on pin 105.
The pump is initially energized when the ignition is switched on to position 2. It will remain energized for a several seconds to pressurize the fuel system. The fuel pump relay will remain energized if the EMS2000 control unit detects the engine is running (RPM via crankshaft sensor). The relay is switched to off immediately if engine RPM is not detected or after ignition key Off is detected.
On early models an inertia switch is installed in the B+ line to the relay between the fuse and the fuel pump relay. In the event of an impact greater than 14G the switch will open interrupting power to the relay. The inertia switch has to be reset manually once it has been triggered.
As of 9/2002 production, vehicles utilize a crash signal from the MRS control unit to the EMS2000 control unit to control fuel pump shut off as oppose to the inertia switch.