KS

[SappySE107]

This sensor is screwed into the block and detects detonation. If knocking or pinging is sensed the ECM will retard the ignition timing to prevent serious engine damage. Depending on the strength of the knock the ECM will pull a set amount of timing very fast and then slowly reduce the knock retard back to 0 or more knock is encountered, whichever happens first.

The circuitry in the knock sensor pulls the +5V input voltage down to 2.5V, the knock sensor then produces an AC voltage that rides the 2.5V DC voltage. A knock will cause a voltage spike in AC voltage that oscillates about the 2.5V bias, if the spike is above 3V it is considered knock.

[rwcar1957]

does the crack or knock sensor have anything to do with the injectors not firing. I change the icm and still the injectors are not firing.

[SappySE107]

The knock sensor won't stop the injectors from firing. Depending on year, the crank position sensor can be the reason injectors aren't firing. That or a blown fuse or bad ground.