Knock Sensor

[Chris Smith]

The knock sensor will do that for you.

You need to time it or look at signals, [a knock and the ignition] but a knock is BTDC, while the combustion is at or very near TDC.

[sometimes after]

One is a soft explosion, the other is a harsh explosion and wave front that the sensor is ideally suited to hear.

But you must be able to use these signals or data to make changes. [scope, etc]