The D-4S SFI system directly detects the intake air mass with a hot-wire type mass air flow meter sub-assembly.
The D-4S system is a fuel injection system which combines direct injection injectors and port injection injectors.
Based on signals from each sensor, the ECM controls the injection volume and timing of each type of fuel injector (direct and port injection types) in accordance with engine load and engine speed in order to optimize combustion conditions.
To promote warm-up of the catalyst after a cold engine start, this system uses a stratified air fuel mixture. This creates an area near the spark plug that is richer than the rest of the air fuel mixture. This also allows a greater amount of ignition timing retard to be used, raising the exhaust gas temperature. The increased exhaust gas temperatures promote rapid warm-up of the catalysts, significantly reducing exhaust emissions.
Stratified Combustion: To achieve stratified combustion, immediately after a cold engine start, fuel is injected into the intake port from the fuel injector assembly (for port injection) during the exhaust stroke. Fuel is also injected from the fuel injector assembly (for direct injection) near the end of the compression stroke. This results in an air fuel mixture that is stratified, and the area near the spark plug is richer than the rest of the air fuel mixture. This allows a retarded ignition timing to be used, raising the exhaust gas temperature. The increased exhaust gas temperatures promote rapid warm up of the catalysts, and significantly improve exhaust emission performance.
Homogeneous Combustion: To optimize combustion conditions, the ECM controls injection volume and timing of the fuel injector assemblies (for port injection) which inject fuel into the intake ports during the expansion, exhaust, and intake strokes. The ECM also controls the injection volume and timing of the fuel injector assemblies (for direct injection) which inject fuel during the first half of the intake stroke. The homogeneous air fuel mixture is created by either combined or individual use of the 2 different types of injectors. This allows utilization of the evaporation heat of the injected fuel to cool the compressed air, and it also allows an increase of charging efficiency and power output.