Have you taken it loose at the tank?
Do nit know your rig's specifics
I took pictures of my brother-in-law installing a new fuel pump.
1) This is a Tahoe
2) These are the Fuel filler hose and the fill vent hose (lets air out of the tank while fuel takes it is space)
3) Hoses removed, See the blue fitting? It has a screen on it.
You cannot see it but the fill hose fitting (The big hole). Also, has a grid or screen in it too. The squares in it were larger than the blue fitting. My hypothesis is this is an anti-somebody sucking your fuel out prevention measure.
Imagine somebody eating a Little Debbie oatmeal cream pie (or two) then stuffing the wrapper(s) in your fuel neck.
First fill up afterwards might shove the wrapper on down and it now mostly covers the grid.
Just a thought, this may not be your answer either. But it would be an easy check!
Images (Click to enlarge)
Saturday, November 26th, 2016 AT 4:30 PM