Could the charcoal canister be plugged? I once read where the F150's had an issue with folks over filling their gas tank; instead of stopping the fill-up when the nozzle shut off, folks would squeeze the handle a couple of more times. This would cause raw gas to drain down the overflow tube, intended to capture the gas fumes into the charcoal canister, and then get re-burned by routing these fumes to the intake manifold. This canister gets clogged with the raw fuel from over filling, and was setting a code.
Is this the same?