This invention relates to an engine for a vehicle using alternative fuel, preferably gas, comprising an engine (5) having a spark ignited ignition system (2) wherein said ignition system (2) includes misfire detection by means of a sensor device (4) providing information to a control system (20), connected to or within said ignition system (2), and wherein said combustion includes diluted operation to optimize emissions wherein said sensor device (4) includes an ion sensing measurement means (40) arranged to measure an ion current in said engine (5) and that said ignition system (2) has a built-in function to detect misfiring through an analysis of the ion current of the engine (5) during combustion.