What is the Knock Sensor?
#2
Scooby Regular
It detects knock i.e. detonation or pre-ignition in the cylinders, basically an uncontrolled burn. This is often heard by a tinkling noise from the outside just before something goes badly wrong. So by attaching a knock sensor to the engine block, the ECU can detect when it's happening and hopefully take steps to reduce it. It's similar to a microphone, but it only picks up sounds of one particular frequency range corresponding to a genuine knock signal in that particular engine. It then outputs a voltage according to how loud this signal is. There is a formula to calculate what the frequency of an engine's knock is likely to be depending on its cylinder size, but I can't remember what it is off the top of my head.
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