iveco daily?

is any body who can help i have iveco daily 2.8 hpi and now start very hard and in not rev more then 1200 rpm and when i press acceleration in very big noise (knocking) and smoke i change 3 injectors and is better but still not power could be sensor on the common rail problem because when i remove plug from sensor engine rev and not knoking but no control of rev
is any body ho can help
thank you