Right think there the same set up as the pd vw engine. If so the injectors have o ring seals on them usually three one below fuel rail one above the one above that for the fuel return or spill system. Did they remove all injectors or just the faulty one. If yes did they replace all the seals. If yes then could be either starter motor or the high pressure pump on the block that's at fault.
If no to all seals it could be them not holding pressure in the fuel rail.
Have you checked oil level fuel can vent into the oil if seals have gone if its high there's the problem.
Be warned if the oil