If there's no deterioration inside any of your fuel hoses - or a cut piece that acts as a flap to cut off flow - I'd suspect the pump. Not sure if yours is rebuildable, but I've seen some vane-types where the vanes get stuck, and they can't build pressure. I've never seen fuel-cell foam that could block anything - what I've seen is very coarse - but maybe there's such a thing out there.