knocking noise an smoke from exhaust

[Jayjaym]

I have an E320 cdi 2005 . It cut out this morning on way to work . I tried to restart it several times but had no joy . AA turned up an put it on diagnostic an lack of valve pressure came up . what does this mean ?? got it restarted but knocking noise coming from engine an white ish smoke coming from exhaust . i have taken engine cover off an 2 injectors look like they have leaked .. they r covered in black stuff . is this the cause of it ?? need advise pls people

 

[Dieselman]

Probably a duff injector or rail pressure control valve.

 

[Jayjaym]

am i looking at big money either way ?