I got this problem with my 3 litre.. it allways knocks on the PFC but we can never hear it at all!!!
I took it to many dyno's and they tuned it with knock levels of around 100 yet there was no detonation because we could not hear it at all.
They told me to ignore the knock level because its not knocking.
My knock sensors used to work ok till the 3 litre went in to maybe we tightend them up too hard ??? how do you know when its in too hard ??? how to you get it right ?