I think more info is needed< when you say they have "gone" failed? leaking ? all four ?

where do you buy your diesel ? have you got a HP pump fault casuing contamination of the injectors ? what symptons are you suffering ?

unless the HP pump is fragmenting and contaminating the injectors. ijectors need checking for leaks first and water in the fuel

You say there is black smoke around the injectors and noise. I think first job is injector removal and fit some new seals. I don't know what the seals are like on yours, but whenever injectors are removed, the sealing washers should be changed. Some have just a thick copper washer, and others have a copper washer and a mild steel "crush" type under the tip. These can be retrieved with a magnet on a stick. Copper ones are fiddled out with a screwdriver and long nose pliers if they fall off the injector. As yours have been out, not too long ago, I wonder if the old seals were re-used?