Mazda 323/MX-3/626/MX-6/Millenia/Protégé 1990-1998 and Ford Probe 1993-1997

Description of System


See Figures 1 and 2

The electronic fuel injection system on your Mazda consists of two subsystems, the fuel delivery system and the electronic control system. The fuel delivery system supplies fuel to the fuel injectors at a specified pressure. The electronic control system regulates the flow of fuel from the injectors into the engine.

The fuel delivery system consists of an electric fuel pump, fuel filters, fuel pressure regulator and fuel injectors. The electric fuel pump, mounted in the fuel tank, draws fuel through a filter screen attached to the fuel pump/sending unit assembly. The fuel is then pumped to the engine compartment, through another filter, and into the fuel injection distributor. The fuel injection distributor supplies fuel directly to the injectors. Constant fuel pressure is maintained by the fuel pressure regulator. The pressure regulator is mounted at the end of the fuel injection distributor, downstream from the fuel injectors. Excess fuel supplied by the fuel pump is relieved by the regulator and returned to the fuel tank through the fuel return line. The fuel injectors spray a metered quantity of fuel into the intake air stream when they are energized. The quantity of fuel is determined by the electronic control system.

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Fig. Fig. 1: Exploded view of a typical 4-cylinder engine fuel system

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Fig. Fig. 2: Exploded view of a typical 6-cylinder engine fuel system

The electronic control system consists of the Electronic Control Unit (ECU) and the engine sensors and switches that provide input to the ECU. The Vane Air Flow (VAF) meter monitors the amount of air flow into the engine, measures air temperature, controls the electric fuel pump and supplies this information to the ECU. Information is also supplied to the ECU regarding engine coolant temperature, engine speed, and exhaust gas oxygen content. Based on the input information, the ECU computes the required fuel flow rate and determines the needed injector pulse width, then outputs a command to the fuel injector to meter the exact quantity of fuel.

On turbocharged engines, exhaust gas energy is used to pressurize the intake air, thereby providing more than the normal amount of air into the combustion chamber. This engine has sensors and provides input to the ECU exclusive to this type of induction, otherwise the fuel injection system on the turbocharged engine operates the same as the normally aspirated engines.