Just FYI a knock sensor "listens" for knock (pre-ignition,
detonation) which is a situation where the fuel/air charge is ignited
before the optimal time. This causes a big problem because the
ignition wants to force the piston down and the crank is still pushing
the piston up. Knock is bad news. In general, the knock sensor tells
the ECU that the engine is knocking and the ECU then retards the
timing or richens mixture to compensate.
Really clever ECUs can have one sensor per cylinder and can deter
knock on each cylinder individually. If you ever hear knocking or
"pinging" and your car doesn't immediately deal with it, then you
should take action to stop the knocking, i.e. stop accelerating or
whatever. Forced induction can cause higher instances of knock.
Using higher octane fuel can decrease the chances of knocking.
Cheers,
Derf
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