Knock sensor or dealer copout?

ElecTech · 07-10-2011, 08:51 AM

I don't wan't to get too deep into this, but the GM knock detection can determine which cylynder is knocking by first, considering which sensor is triggering (front/rear or in later years left/right). Then, it will use the current crank position and firing order to determine the offending cylinder. It also can control firing events on a cylinder by cylinder basis.

As far as misfires go, understand that the PCM does not detect a misfire, per se, it only detects rotational speed variations between predicted firing events. So any condition that causes a variation in rotational speed can be viewed as a "misfire" by the PCM. It doesn't have to be an actual lack of or incomplete combustion.

I'm in no way supporting the techs claims, just wanted to clarify a few things.

I hope you get it figured out soon. These situations can be very frustrating.

Good luck.

07-10-2011, 08:51 AM	#11
ElecTech Senior Member Join Date: May 2009 Location: Charleston, SC Posts: 1,489	I don't wan't to get too deep into this, but the GM knock detection can determine which cylynder is knocking by first, considering which sensor is triggering (front/rear or in later years left/right). Then, it will use the current crank position and firing order to determine the offending cylinder. It also can control firing events on a cylinder by cylinder basis. As far as misfires go, understand that the PCM does not detect a misfire, per se, it only detects rotational speed variations between predicted firing events. So any condition that causes a variation in rotational speed can be viewed as a "misfire" by the PCM. It doesn't have to be an actual lack of or incomplete combustion. I'm in no way supporting the techs claims, just wanted to clarify a few things. I hope you get it figured out soon. These situations can be very frustrating. Good luck. __________________ Jaime