crashzx6r

can someone explain what a knock sensor is....

LUV2XLR8

Its a sensor mounted on the engine that is designed to detect the high-frequency vibrations caused by detonation

5-90

A knock sensor is a piezoelectric device that uses a slice of quartz crystal to generate a voltage pulse when a "knock" is detected.

Piezoelectricity can be looked up for an explanation better than I can give - but it's a principle whereby certain crystals will generate an electrical pulse in response to mechanical stimulus.

When everything is running just four-O, the knock sensor is along for the ride. It only generates a signal when something goes wrong - at which point the timing is adjusted (advanced) until the knocking stops, and then it is gradually retarded until a balance is struck where the engine no longer knocks.

Knocking ("spark knock") is often caused either by detonation - which can be caused by excess carbon deposits - or by preignition - where something gets to glowing red hot and lighting off the fuel before the spark gets a chance to. Preignition is typically caused by carbon deposits, but can also be caused by casting flaws, cracks in the metal surface, or any unbroken sharp edge in the combustion chamber (which becomes a heat concentrator.)

solderjunkie

5-90's got this one.

Good show, Mang