Electronic Fuel Injection - EFI

Fig. 1 Fuel delivery sub-system:

This fuel injection system is a multi-point, pulse time, mass air flow fuel injection system. In this system, fuel is metered into the intake air stream according to engine demand through injectors mounted on a tuned intake manifold.
An on-board vehicle electronic engine control (EEC-IV) computer receives inputs from various engine sensors. It uses these inputs to compute the required fuel flow rate needed to maintain an ideal air/fuel ratio throughout the entire engine operational range, then outputs a command to the fuel injectors to meter the amount of fuel injected.
The fuel delivery sub-system consists of an in-tank low pressure pump, a high pressure chassis mounted electric fuel pump and the necessary interconnected tubing, Fig. 1.
Fuel drawn from the tank passes through a filter before entering the low pressure pump. The fuel is again filtered as it leaves the high-pressure pump on its way to the pulse damper and fuel supply manifold. The pulse damper smooths the pressure variations generated by the opening and closing of the fuel injectors.
The fuel supply manifold assembly includes electrically actuated fuel injectors directly above each of the four intake ports. The injectors spray a metered quantity of fuel into the intake air stream, when energized. A constant fuel pressure drop is maintained across the injector nozzles by a pressure regulator that is connected in series with the fuel injectors and is located downstream from the injectors. Fuel supplied by the pump that is not required by the engine passes through the regulator and is returned to the fuel tank through a fuel return line.
Two injectors are energized simultaneously, once every crankshaft revolution. The period of time the injectors are energized, known as injector ``on time'' or pulse width, is controlled by the Electronic Engine Control (EEC) computer. Air entering the engine is measured by a vane air flow meter positioned between the air cleaner and turbocharger. This air flow is then compressed by the turbocharger before being introduced into the intake manifold. This air flow information, in conjunction with various other inputs, is used to compute the required fuel flow rate.