Help ! Help !

Quick Story

July 01 Piston melted in No:2 Bank........ New Engine fitted

Problem

@ 3800 - 4200 rpm Engine holds back...juddering all the way thru

to 7000rpm some days good some days bad

use Optimax

3 Dealers can find no problem, suspect Knock sensor. No fault codes

stored

Engine not misfiring

New dump valve fitted, and all new parts with new block

Help !