Knock Sensor

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Knock Sensor

Knock sensors are found on all JDM H22 engines, and the UKDM H22a7 & H22a8.

A knock sensors is basically a microphone and plays 2 roles in the engine:-

  • 1) monitor engine operation to optimize performance (and saving fuel in the process)
  • 2) protect the engine against power-robbing and potentially destructive engine knock.


Location:

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The knock sensor can be seen right below the intake manifold, above the water pipe; the black connector.


How is knock caused?

Knock occurs when the air-fuel mixture doesn’t burn smoothly or is ignited too soon.

  • 1) Knock can be caused by “hot spots” in the cylinder, such as carbon deposits or spark plugs that are too hot for the engine, sharp edges on the piston top, or high combustion chamber temperatures. These hot spots ignite the air-fuel mixture before the spark plug fires.
  • 2) Knocking also occurs if spark timing is advanced too far and the spark occurs while the piston is too far before TDC, causing a collision between the rapidly expanding gases from combustion and the top of the piston as it moves up the cylinder wall.
  • 3) Some engines are prone to knocking. The engines that are likely to knock are usually high performance and poorly maintained. Both situations require the engine to continually operate at the edge of knocking.
  • 4) Using petrol with a low octane rating can cause knocking.
  • 5) Anything that increases combustion chamber temperature can cause knocking such as failure of the EGR, a cooling system problem, burning engine oil, or incorrect spark plug heat range.
  • 6) On an older vehicle, especially one used primarily for stop-and-go driving, deposits can build up in the combustion chamber leading to the hot spots that cause knocking.


How does the ECU use the knock sensor?

The knock sensors sends a base or “no knocking” reference signal to the ECU. If knocking occurs, the sensor detects the increased vibration and increases its signal to the ECU. The ECU then slightly retards timing until the sensor signal returns to the reference level.