Fuel Delivery and Air Induction: Description and Operation

DME System Diagram:

The fuel system provides storage space for the fuel, delivers fuel to the engine, admits filtered air to the engine to be mixed with fuel, and mixes fuel and air in correct proportions and delivers the mixture to the cylinders as a combustible vapor.

The fuel system consists of the fuel tank, electric fuel pump, fuel filter, fuel injector rail, pressure regulator, injection valves, air filter, induction system, DME control unit, and fuel supply and return lines.

An electric roller-cell type pump feeds fuel from the tank through the fuel filter into the fuel injector rail. The fuel injector rail supplies each electronically controlled injection valve equally with fuel. At the downstream end of the fuel injector rail the pressure regulator holds a constant pressure differential between fuel pressure and manifold pressure; excess fuel is directed back to the fuel tank. Because of the constant flow, cool fuel is always available, which prevents formation of vapor bubbles and ensures good hot starting.

The fuel system is controlled by the Digital Motronic Engine system (DME) which precisely controls fuel injection under variable operating conditions. Various engine sensors and other systems (i.e.. air conditioning, auto transmission etc.) supply the DME control unit with operating information. The DME control unit processes the input information and sends output signals to adjust injector pulse width and ignition timing. Refer to COMPONENT OPERATION for detailed operation of the DME control unit.