i bought a used vg30de motor from jdm engine depot for my 1990 300zx 2+2
the engine starts but its noisy and my oil pressure on the dash wont go up....
i was told it could the oil pressure sending unit / sensor, or the oil pump it self
not sure what exacty is the problem

if anybody could help me out and explain what could be the problem i would appreciate it

Could be the oil pump. I'm guessing that there's oil in the crankcase?