Basics:
Engine Knock is the premature combustion of fuel in the
piston chamber. Other names to describe
engine knock are pre-
ignition,
detonation, or knocking. Basically the fuel in the chamber has ignited before the piston has reached the top of its travel and obtained full
compression.
Causes:
Engine Knock has many causes, some of the most common tend to be people using under-rated octane fuel for their vehicle. You absolutely cannot put 89 octane in a vehicle that requires 93. A silly attempt like this to save money will cost you thousands. Other causes for engine knock is over-advanced timing, or elevated Exhaust Gas Tempatures which are due to a lean condition.
Detection:
Knock Sensors are used to detect engine knock, when an engine produces knock, it creates an irregular vibration (which is also audiable) in the engine. When the computer senses knock, it retards ignition timing in order to stop it.
Dangers:
Continous engine knock is one of the many signs that can present themselves when there is a larger problem present. The ECU will constantly make attempts to avoid engine knock, persistant knock will damage pistons, piston rings, spark plugs, fuel injectors, and piston chambers.
Avoidance:
The ECU will do its best job to avoid knock, always use the recommended fuel octane for your vehicle, regardless of price. If you continue to experience knock, try an
octane level higher than what you're using, or take your car to the shop. A few extra dimes for higher octane is better than a few thousand dollars for a new engine.