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A miniature sensor for detecting cylinder misfiring based on the principle of magnetostriction has been developed for on-board use in production vehicles. The sensor induces a magnetic field in the engine crankshaft, and via Faraday's law, obtains a signal directly related to the strength of the field. Due to magnetostriction, the field strength changes as the stress in the crankshaft changes during each cylinder firing. The output signal of the sensor is therefore high when any given cylinder fires and low when it misfires, permitting ready determination of misfiring. Tests on a manual transmission vehicle have shown that a single sensor can detect misfiring in one or more cylinders at any non-negative torque and any speed, as well as on very rough roads. Other uses for the sensor, such as knock detection, are anticipated.