Common rail pumps do have to be timed! The pump is like a mini, opposing 2 cylinder motor. There are 4 injectors, they time the pump so when it's creating the most pressure on one of the strokes of the pump it coincides with when one of the injectors is firing. That way the injector is getting the most pressure the pump can produce right at the same time a it injects. If it's not timed the injectors will be getting pressure created when the pump is in the middle of a stroke and not top dead center at its highest pressure produced. Make sense?