Ford: ford fuel system, fuel vapors, ford system

Question
hi Candie,
i have a '01 explore and i'm hoping to figure out how the fuel system works and differs from my past vehicle which was honda. is ford system a fairly low pressure, since i don't hear the normal hiss when opening the cap? instead of screw on fuel cap, it has a twist and snap on one with spring and opening in the middle, does it release fuel vapors into the canister right through that or adjacent tube to the tank extension filler tube? it has a fuel vapor canister that collects fuel vapors, is the onboard computer able to determine or analyze release of excessive fuel vapors if any are escaping thru the neck, cap or nozzle restrictor? also, the little flipper or nozzle restrictor in the tank extension hose is flimsy, does that have any purpose other than preventing junk from falling into the tank, or does it also prevent excessive fuel vapors from escaping? the reason i ask this is because i notice some strange fuel level. for instance, one day i'll park it the fuel level will be at 1/2 and couple of days later, i'll start it and level will drop a 1-2mm of that mark. i realize that temp has an effect, but it's only .00064 or so for every degree of temp of each gallon of fuel, which should be hardly noticeable. but then, should the onboard computer detect a smallest of any leak even thru the restrictor or any place else? any other suggestions or ideas? thanks for your time.

Answer
Fords are just funny creatures and they tend to lose gas when started but the gauge should go back up after about 15 minutes of driving.  It is a low pressure system and the nozzle restrictor is an anti syphon device to help you from people stealing your gas.