knock sensor

A knock sensor is generally used on turbocharged or high compression performance engines. The knock sensor is generally screwed into the engine block for all cars. To test the knock sensor, generally you can tap a wrench on it as it runs. The engine should change idle speed as the timing retards. If the idle speed doesn’t change, try again at a slightly higher rpm. If the speed once again dosen’t change the knock sensor probably doesn’t work. High performance engines are alot more prone to detonating when they are under boost. The timing on a turbocharged engine should retard when the boost comes on. If the boost would go too high the timing will be too advanced for the higher boost and will detonate. If the engine detonates it builds very high pressure waves. This can damage the engine’s pistons, bearings and crankshaft. The knock sensor senses the very high frequency pressure waves ocurring inside the cylinder. If the knock sensor is tightened too tight or is too loose it can effect the measurable frequency band. The tightening torque depends on the knock sensor specification for that engine. If it is incorrectly tightened it will sense other vibrations in the engine and incorrectly believe that there is a problem. The knock sensor works by simply retarding the timing until the detonaton quits. The driver should feel the significant decrease in power as it retards. It saves the engine from detonation which will break pistons and burn up head gaskets.