On my 78 Fury, as soon as I left the place I bought it from I tried to fill it at the 1st gas station I came to. I put 8-1/2 gallons in it and it acted FULL.
the gauge still showed just over 1/4 (I think I know the solution to THAT part of the problem). Anyways I ran it outta gas and poured a can (~5 gal) into it and went home then back to town with a stop at the station. I barely squeezed $10 in there (3.something gallons.) Added to what's left of the can-o-gas I put in on the roadside, that don't add up to full. The owners manual says 19-1/2 gallons capacity. What would cause not being able to actually FILL the tank?? And no, its not caved in.

Clogged or misrouted fuel tank vent lines can cause this. Pressure builds up in the tank, the nozzle senses the pressure and cuts off.

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