Increase mpg
You get more Miles Per Gallon if the tank is full. To prevent the fuel tank from bursting it vents fuel vapor out to reduce pressure. Have you notice how far can you go without the needle moving? Before I taught that it was only due to lag but after filling it up I was very surprise how less fuel was consumed. At first I taught the fuel tank vent was not working properly.
As needle approaches F, fuel efficiency becomes infinite?
Let's call it the Theory of F150 MPG Relativity.

