How is a misfire detected?

[fastcougar]

How does the engine know to record a misfire event in the OBD-II system? How is the misfire detected?

 

[GR899V8]

Trevor,
On my '99, the sensor on the engine knows the RPM's. If there is a teensy drop in the RPM's, it can tell which cylinder it is by comparing the drop in RPM to the cylinder that should be firing at that time. It locks in a code telling you which cylinder it is. I, too wondered how it knew my #7 cylinder was not firing!
dOn

 

[fastcougar]

Posted this question on my board (I own/admin Dead Link Removed) and someone posted this:

SAE Document p 4-7 discusses misfires

 

[GR899V8]

Oh, I thought you really didn't know and wanted a quick answer. Good info, thanks.