ZD30 engine can I crack injector nut ?

Engine died and wont restart. Removed intercooler. I can now see the nut that connects injector pipe to injector.
Question. can i njust undo the nut so i can tell if fuel is being pumped, or do I need to dismantel things further so i can also put a spanner onto whatever that nut is screwing onto.
Im worried if i just put a spanner on the nut and try to loosen it, I will twist/damage whatever is inside the rocker cover
Thanks

Nah. Just crack it mate. Shouldn't be an issue. As long as you're talking about the nut holding the line to the injector.

Dickhead, used my brains and cracked the nut other end of the line, on the pump. Undid it 3 or 4 flats, reached inside with the door open so i could watch and hit the starter,,,,,,,, not even a drop,,,,,Hmmm.

That was me i was calling a dickhead.

Maybe NATS related then?