Cylinder 1-8 Knock PID's

[mowton]

Can anyone explain how the Cylinder 1-8 knock PID's operate. Does the PCM take the current knock values and assign them (either all or weighted) to the current cylinder(s) in Power stroke or is there some other methodology to its application. I have an example where cylinder 6 and 8 seem to be predominant, while all the other cylinders seem to get an equal "small piece" of the knock...they seem to follow? Unfortunately I only have one example at this time.

Have a client/setup that gets very random (maybe once in 30-45 min log), very short lived (normally 2 quick hits/decay within 3-4 secs) knock at mid load.... but none at wot.......LS7, stout cam (22 degrees overlap), flex sensor mod and E85.


Thanks

Ed M

[schpenxel]

I messed with this for a while once, but it's been a while... from what I recall the individual cylinder reporting seemed to only be reported correctly under relatively stable (non transient) conditions.

Almost anytime I was accelerating or making a throttle change or anything like that KR tended to show up on all cylinders fairly equally (this was on 2.24 also so it was a bit slower / harder to tell). Or maybe I just had knock in all cylinders?

If I was in steady state or just slowly accelerating, etc. then KR would sometimes show up on individual cylinders totally separately

Just my experience. I'm interested in hearing how this has worked for others too

[sssnake]

If you have a single cylinder knocking you will see higher knock retard (degrees) on that cylinder and lower everywhere else. If you have sporadic knock from all it shows up fairly evenly across cylinders. In the sporadic case at low RPMs you will typically see one higher than the other but the highest value moves around from cylinder to cylinder. At higher RPMs it evens out across the cylinders. At least this is what I am seeing. I confirmed the behavior across 4 cars so far so not conclusive but at least a trend.

It also makes sense when you think of how these sensors work. The piezo in the knock sensor is just an acoustic sensor. The knock sound will be higher magnitude on the cylinder that has knock but there will likely still be sound when the other cylinders fire. With sensors only on each bank, the ECM has to determine when it heard the sound and what cylinder is firing at the time when the magnitude is the highest.