Fuel Pump Control Circuit

SYSTEM: Fuel Pump Control Circuit

CIRCUIT DESCRIPTION

In the diagram above, when the engine is cranked, current flows from terminal ST of the ignition switch to the starter relay coil, the starter relay switches on and current flows to coil L1 of the circuit opening relay. Thus the circuit opening relay switches on, power is supplied to the fuel pump via the fuel pump relay and the fuel pump operates.
At the same time, the engine speed signal NE is input to the engine control module. This turns Tr1 in the engine control module on and causes current to flow to coil L2 of the circuit opening relay, thus keeping the contacts on.
The fuel pump speed is controlled at two levels (high speed or low speed) by the condition of the engine (starting, light load, heavy load). When the engine starts (STA ON), Tr2 in the engine control module is off, so contact B in the fuel pump relay closes and battery voltage is applied directly to the fuel pump. Fuel pump operates at high speed.
After the engine starts, during idling or light loads, since Tr2 goes on, current flows to the fuel pump relay coil, contact A closes and power is supplied to the fuel pump via the fuel pump resistor.