During the 11/12/11 Show, they advised a woman that the one transgression of driving away from the gas pump with the nozzle in the filler pipe while distracted by a bagel did not create the problem of a check engine light. I disagree. Subarus have a feedback fuel system that relies on the tank being vented properly, including a tube that goes to the top of the filler pipe. If that system is not allowed to vent / equalize, the manual and the fuel door (at least on my Legacy) warn you that topping off the tank harms that system and will cause the light to come on. Therefore, couldn’t the bending of the filler pipe crimped the fuel feedback system, thus causing the same kind of problem that overfilling would cause?
That is along the same lines as what I was thinking when the brothers advised this woman that her problem was “heat soak” of electronic components, such as a coil.
While they could turn out to be right, I initially thought that the woman’s problem was related to the evaporative emissions system. Then, when she revealed that she has an occasional illuminated CEL + that she may have damaged the fuel filler neck with her “distracted by a bagel” fiasco, it reinforced my thoughts that her problem is related to the evaporative emissions system.
I’m inclined to agree. That tube that routes from the gas tank to right next to the fill hole is part of the evaporative emissions vapor recovery system. It’s small, and if she created enough lateral pull on the fill pipe it could easily create enough force to pinch it closed. Yes, that could cause an intermittant CEL.
It’s a bit diferent failure mechanism than that of overfilling the gas tank. There’s also a vapor line between the fill pipe and the charcoal canister, and overfilling on some vehicles can cause gas to get to the charcoal bed and saturate it.
Attached is a schematic of my system, a typical system.