Iveco 75E15 R reg very poor power, pump knocking?

Iveco broke down on road, wouldn't start, just turning over - bleed fuel up to injectors and started and ticked over fine, drove 1/2 mile up the road and lost all power and knocking coming from fuel pump, managed to drive it back with no power. Removed the fuel pump and sent away to be reconditioned and they said pump was ok. What else could cause lack of power and the pump to knock?

Any Ideas much appreciated, Many Thanks