we have a fuel gauge on it and was reading it, stated that in op.
the guy brought it to us becaus eit quit running and he couldnt get it started. and if he did it wouldnt run but fora minute, he pulled fuel filter cap on the engine and would be full of air bubbles.
i done the test like described on the bottom of this page Diesel Technician Society
and got more air bubbles than they showed in there video. so im guessing its an injector copper sealing washer.