Circuit Description

When engine is cranked, current flows from terminal ST of ignition switch to starter relay coil. Current also flows to terminal STA of ECM (STA signal). When STA signal and NE signal are input to ECM, Tr1 is turned on, current flows to coil of circuit opening relay, relay switches on, power is supplied to fuel pump and fuel pump operates. While NE signal is generated (engine running), ECM keeps Tr1 on (circuit opening relay on) and fuel pump keeps operating. Fuel pump speed is controlled at two levels (high speed or low speed) by condition of engine (starting, light load, heavy load). When engine starts (STA on), Tr2 in ECM is off. Fuel pump relay closes and battery voltage is applied directly to fuel pump. Fuel pump operates at high speed. After engine starts during idling or light loads, since Tr2 goes on, power is supplied to fuel pump via fuel pump resistor. Fuel pump then operates at low speed.