[ACademic]

FYI, you can inspect this without removing the shield. The vent hose should attach to the top of the tank with one worm clamp. If you don't see any obvious kinks, then remove the hose from the tank end, open up your fill cap, and blow some compressed air out toward the fill cap. That will ensure that you don't have any debris lodged in there and you're blowing it out the car rather than in the tank. Or, better yet, use a shop vac and place the tank end of the hose into the suction. The vent is (I believe) either 5/8" or 3/4" ID, so I'm suspecting you have a bend/kink.