Purpose

Knock Sensor (KS) System Description:

Ignition timing is the relationship between the time the spark plug is fired and the time that the piston reaches the end of the piston's upward travel in the cylinder (TDC). If the spark plug ignites the compressed air/fuel mixture too late, not all of the air/fuel mixture has time to burn while the fuel is highly compressed. Late ignition causes a decrease in fuel efficiency, decreased power, and increased exhaust emissions. If the spark plug fires too soon. Too much of the air/fuel mixture starts burning before the piston reaches the top of the compression stroke. Early ignition of the air/fuel mixture causes detonation, commonly referred to as spark knock. Constant spark knock in the motor is undesirable. Excessive spark knock can reduce engine performance. If severe enough, detonation can cause engine damage. Every engine has an optimum ignition timing value. Optimum ignition timing is usually the earliest or most advanced firing of the spark plug that is possible without causing detonation. An engine's optimum ignition timing is designed to be the most advanced ignition timing possible during the most demanding conditions. Optimum ignition timing is affected by all of the following variables:
^ Engine load
^ Engine temperature
^ Air density (atmospheric pressure)
^ Fuel quality
^ Fuel octane rating

Ignition systems equipped with a Knock Sensor (KS) can be engineered for optimum ignition timing. A knock sensor (KS) can enable the Powertrain Control Module (PCM) to adjust ignition timing in order to adapt to any of the variables that affect optimal ignition timing. The KS detects when the engine is experiencing detonation. The KS then signals the PCM to reduce spark advance until detonation is no longer detected.