So I changed my fuel tank and used a B-body tank. No problems with using the b-body tank but it didn't have a built in vent. The new sending unit had a supply line and a vent line but I used the vent line for my fuel pressure return line. So now my tank doesn't have a vent. Last night I have drove the car about 20 miles and when I got home I could hear the electric fuel pump whining loader than normal. I should have pulled cap at that time to see if the tank had a vacuum in it but it was late. This morning I started it up and the pump sounded normal. Anyway I'm thinking a vented fuel cap should solve the problem as I don't want to drill a hole in my tank. So my question is has anyone used a vented cap and if so what one. My other option would be to pull the filler neck and weld in a vent tube that leads up above the tank behind the bumper.