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 Tempature]s which are due to a lean condition.

Detection:
[Knock Sensor]s 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 [piston]s, [piston ring]s, [spark plug]s, [fuel injector]s, and [piston chamber]s.

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.

engine knock (thing)