Fuel Injection System

The Sequential Multiport Fuel Injection (SFI) system is classified as a multi-point, pulse time fuel injection system. Fuel is metered into each intake port in sequence with the engine firing order. The fuel is pulsed through four fuel injectors mounted on a tuned intake manifold. Fuel amount is determined by engine demand.

An on-board Powertrain Control Module (PCM) accepts input from various engine sensors to compute the required fuel flow rate necessary to maintain a prescribed air/fuel ratio throughout the engine operational range. The PCM then sends a command to the fuel injectors to meter the appropriate quantity of fuel.

The fuel delivery sub-system contains a high-pressure, in-tank fuel pump. The fuel pump delivers fuel from the fuel tank through a 20 micron fuel filter to a fuel injection supply manifold.

The fuel injection supply manifold incorporates electrically actuated fuel injectors directly above each of the engine's four intake ports. The fuel injectors, when energized, spray a metered quantity of fuel into the intake air stream.

A constant fuel pressure drop is maintained across the fuel injector nozzles by a fuel pressure regulator. The fuel pressure regulator is connected in series with the fuel injectors and is positioned downstream from them. Excess fuel supplied by the fuel pump and bracket, but not required by the engine, passes through the fuel pressure regulator and returns to the fuel tank via a fuel return tube which is part of the fuel and vapor return tube.

The period of time that the fuel injectors are energized (fuel injector "on time" or pulse width) is controlled by the PCM. Air entering the engine is monitored by flow, pressure and temperature sensors. The outputs of these electronic engine control sensors are processed by the PCM. The PCM determines the needed fuel injector pulse width and outputs a command to the fuel injector to meter the exact quantity of fuel. Each fuel injector is energized once every other crankshaft revolution in sequence with the engine firing order.