Spark-ignition engine controller

An engine has four cylinders (2A-2D) each with a piston and a combustion chamber with a spark plug connected to the ignition circuit, while fuel is injected by an injector (9) with a needle valve and a solenoid. An oxygen sensor (23) connected to a three-way catalyst (24) measures the air-fuel ratio and a control unit controls the fuel supply to the cylinders so that combustion is performed with a lean air-fuel mixture.