Controlling supply to fuel pump

Controlling supply to fuel pump

Control of fuel pump (A) is through the ECU which is responsible for turning on pump, by means of relay (B), during start-up and normal engine operation.

With ignition switch in MAR position (15/54), power is supplied simultaneously to pump relay (B) and main relay (C), which closes to provide power to the ECU (terminal 1).

A special circuit in the ECU earths pump relay (B) through terminal (25), which in turn supplies fuel pump (A) with power through a 10 A fuse. The pump puts the fuel system under pressure for about 1 - 2 seconds.

When the engine is started up, an rpm signal from rpm and TDC sensor (D) reaches terminals (16 and 32) of the ECU. After about 1 second, relay (B) is activated and the pump thus stops (for safety reasons) even with the ignition switch in MAR position.

If battery voltage drops below rated level (e.g. during cold starting), the fuel feed pressure tends to drop.

To overcome this drawback, the ECU increases injection time proportionally in accordance with a correction factor to ensure accurate fuel metering at all times.