Knock sensor off-car

Knock Sensor:

This sensor is pretty much in all the modern engines and it lets the ECU know if there are any knockes or detenations inside the cylinder . These knocks are produced by the engine when the timing is poor or if there is detenation due to too much advanced timing or a very lean fuel/air ratio mixture .The ECU also uses this to balance the timing if it is controlled by the ECU and to lean the air/fuel mixture or richen it if knocking.

This sensor uses piezo crystal and one of this crystal properties is when deform it creates a voltage . Knocking inside the cylinder causes the crystal to vibrate and therefore it creates a voltage to be sent back to the ECU so it can rectify it and delay the advance timing to stop it form knocking or richen the air/fuel mixture .

By connecting the sensor to oscilliscope and tapping the knock sensor we can see how this sensor works .