We left it running long enough yesterday to go closed loop, and from Tech2 side, no sign of overfuelling, trims looked about right, lamdas going rich/lean/rich/lean as expected.
All 3 of us agree the noise is from 1/3/5 bank, but can't agree which pot - my own feeling being 3 or 5, but so hard to pinpoint. Listening stick didn't really help either.
I think the 3 of us have now ruled out:
Foreign objects in cylinder (unless embedded in piston, and clouting head) - good compression on all 6, absolutely no sign of any damage to any plug.
Ignition - changed leads and plugs.
Overfuelling - Kevin Wood in the week has checked injectors, and changed injectors, and FPR. Tech2 data seemed normal when it went closed loop.
Lifters on the side we think the noise is (inlet and exhaust, and inlet only on 2/4/6 bank) - visually checked.
I think the 3 of us are 100% completely out of ideas as to what to try next.
:-/