Originally Posted by f1100turbo
Make sure if your cap is vented that you get a vented cap or vice versa .
The cap should not be vented. The tank vents through the emissions control equipment to prevent gasoline vapors from escaping from the tank. If the gas cap is loose or a vented cap is substituted it will will display a gas cap icon on the instrument panel.
PS I didn't see it in the original post, but I assumed he has a gasoline Ford chassis. The same comments should apply to a gasoline Chevy, but I don't know for sure. If it's a Diesel, ignore my comments.