is called a flap trap
"Flap trap"? Not really important in the grand scheme of things. Could also be an anti siphon hose flap.
try google it also
Does anyone know the exact name of the spring loaded cap at the end of the filler neck called? I am speaking of the silver "door" that folds back when you put the nozzle from the gas pump into the tank. It looks like an aluminium circle. Also if it's missing or broken could that be the cause for low fuel efficiency and will getting a tune up help?
