Injector??

Ever since rebuilding our 200tdi discovery engine fitted to a defender, its nevver ran correctly a bit low on power and rough idling. we loosened the injector pipes on each injector whilst it was running and noticed the first injector makes no difference to the running of the engine if loosened unlike the other ones. Could it be a lazy injector?, is it worth swapping?

What if you swapped the injector with another cylinder's, did the same test and had the same result on the new cylinder location, that would seem to isolate it to the suspected faulty injector.

Those injectors look cheap on Paddocks too anyway.