Engine Engine keeps flooding out

Yes, the smaller line is the return
Simply check the fuel pressure and regulator operation to see if it is plugged
We used to have to block off the fuel return line to use the Rotunda (Ford) injector cleaner equipment
When you do that, the regulator vacuum on or off will have no effect
Never seen one plug up. Why are you thinking yours is plugged? Pig Fat Rich?
Better check the codes