Injector knock! Help

[Dwg_23]

Hello, I have a 2005 c220 cdi, it's been in a local garage and had 2 "refurbished" injectors fitted, when I got it back its has a diesel knock and rough running, as if its firing on 3? Any ideas?

 

[Frontstep]

Take it back, unless you were told of the problem.

 

[Dwg_23]

Yeh it's gone back, and just like to be armed with and idea of what it is myself!