Japanese Mitsubishi Knock Sensor

Also known as engine ping or detonation, an engine knock is a sound and reaction that occurs when there is a second unplanned ignition or explosion within a cylinder that is separate from the regular controlled ignition from a spark plug. In other words, knock is bad news for your engine. A few things must happen for this to occur.

Basically, the spark plug ignition creates a flame front that travels through the remaining cylinder space. That flame front’s movement pressurizes the remaining air and fuel mixture. Increased pressure means increased temperature, and in some cases, it gets so hot that it creates a second ignition. The second ignition creates a second flame front, and when those two reactions collide, you get knock.