Fuel Vapor Issue, seemed really strange

[HR-OLIFANT]

Ran some errands in the truck today, parked it on the street around 1pm. Total run time was around 30 minutes. The street has a slight slope, so the filler door was on the down side. Temps today were in the low seventies.

Took the kids to the circus, got home around 6:30 when the wife notices a drip from the rear splash guard. It was a slow gas drip from the cap. I loosened the cap a bit and fuel sprayed out under great pressure. I started the truck to see if that would relieve the pressure, which it did not. After shutting the rig down, I opened the cap fully, which resulted in quite a bit of fuel gushing out before a huge air burp released. I ran a search here and it seems I need to check a few things:

A. The charcoal canister
B. The lines inside the quarter panel for clogs
C. ?

Any thoughts or suggestions on what else I should be checking?

Also, it seems that some fuel may have been leaking from the gasket area inside where the filler tube attaches to the body. I am assuming that this was due to the pressures involved.

 

[Trapper50cal]

Is it an aftermarket gascap? If so, is it a vented model? A vented model may help release the pressure build up...

Did you ever have Capri Sun juice pouches when you were a kid? Did you ever "pressurize" them by blowing through the straw? Then it would come shooting out...

 

[HR-OLIFANT]

It is an aftermarket cap, but this cap has been in use for almost ten years, so I can't imagine it is now the culprit. I am about to dig into it in an hour or so. I may go ahead and replace the cap anyhow, because there is some cracking of the rubber at the contact points.