2004 Ford F-350 Super Duty Q&A

2004 Ford F-350 Super Duty Question: return brings out air-bubbles when i crank; when i stop its return comes normal

when i crank the car the return brings out air like bubbles but when i stop cranking the return comes normal. i have change the fuel pump but am still have the same problem. -
Answer 1
Out of fuel. -
Answer 2
fuel pump is poss failing -