The knock sensors (KS) job is, to monitor the engine, for any signs of detonation.
Consequently, detonation is the premature ignition, of the air fuel mixture.
Detonation is a sound that occurs, when there is a second unplanned ignition within a cylinder. However, it is separate, from the regular controlled ignition from a spark plug.
Knock sensors (KS) monitor this frequency, because; the second ignition, creates a second flame front. As a result, when those two reactions collide, you get a knock. Detonation produces, a distinct, mechanical knocking sound. But, is usually detected, at higher engine speeds or a sudden increase in engine load.
So, to prevent detonation, knock sensors, monitor the frequency, at which normal detonation occurs. Consequently, providing the (PCM), with a continuous live data stream, that allows the (PCM), to control the ignition timing.
Then, to improve engine efficiency, the (PCM) keeps the ignition timing, as far advanced as possible. Based on the current operating conditions; such as, engine speed, load, throttle position, and vehicle speed.
So, if the knock sensors detect, a change in that frequency; it will generate a new signal voltage. Consequently, that signal voltage is based on the changed frequency. Which the (PCM) then interprets as detonation.
So, to correct this condition, the (PCM) then retards the ignition timing. But, only when the detonation frequency matches a wave amplitude; that is based on, a pre-programmed value.
So, the advantage of this is, that the (PCM), can always keep the ignition timing advanced. Therefore, suitable for any given set of engine operating conditions. As a result, increasing engine efficiency and fuel economy; while reducing emissions. In other words, defective knock sensors have, a direct bearing on engine operation and efficiency.
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