About knock sensor:

The knock sensor detects abnormal vibration (spark knock or pinging) in the engine. The knock control system is designed to reduce spark knock during periods of heavy detonation. This allows the engine to use maximum spark advance to improve driveability. The knock sensor produces an AC output votage which increases with the severity of the knock. The signal is fed into the PCM and the timing is retarded to compensate for the severe detonation.

所以knock sensor还是很重要地, 太强的爆振(detonation)会损坏曲轴,联杆, 和气门挺杆.那问题就大了.