Overview of the Fuel Delivery System

The fuel delivery system incorporates the following components:

1) Fuel tank (with evaporative emissions controls)

2) Fuel pump

3) Fuel pipe and in line filter

4) Fuel delivery pipe (fuel rail)

5) Pulsation damper (many engines)

6) Fuel injectors

7) Cold start injector (most engines)

8) Fuel pressure regulator

9) Fuel return pipe

Fuel is pumped from the tank by an electric fuel pump, which is controlled by the circuit opening relay. Fuel flows through the fuel filter to the fuel rail (fuel delivery pipe) and up to the pressure regulator where it is held under pressure. The pressure regulator maintains fuel pressure in the rail at a specified value above intake manifold pressure. This maintains a constant pressure drop across the fuel injectors regardless of engine load. Fuel in excess of that consumed by engine operation is returned to the tank by way of the fuel return line. A pulsation damper, mounted to the fuel rail, is used on some engines to absorb pressure variations in the fuel rail due to injectors opening and closing.

The fuel injectors, which directly control fuel metering to the intake manifold, are pulsed by the ECU. The ECU completes the injector ground circuit for a calculated amount of time referred to as injection duration or injection pulse width. The ECU determines which air/fuel ratio the engine runs at based upon engine conditions monitored by input sensors and a program stored in its memory.

During cold engine starting, many engines incorporate a cold start injector designed to improve startability below a specified coolant temperature.

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