Abstract: In a combustion engine, such as a diesel engine, the periodic displacement of an engine component member having a cyclic function directly related to the piston stroke of an engine cylinder, is detected by a proximity sensor disposed adjacent to an area through which the component member is periodically displaced, the sensor providing a series of cylinder identification (CID) signal pulses having a peak amplitude in dependence on the spatial distance between the sensor and the member at that position in its displacement cycle at which it is in close proximity to the sensor, and having a period in dependence on the periodicity of the member displacement cycle, the occurrence of each CID signal pulse being directly related to, and representative of the piston stroke through a reference piston position.