What could possibly make my gas cap pop out of the tank as the attendant unscrewed it to fill up with fuel?

Let me start from the beginning I have had idle problems which led me to the popped out gas cap she starts up and drives well till at one point she stalls the FPR hose is kinked so will replacing the unit and hose correct the stalling? To my memory this FPR unit has never been changed.

Gasoline has a relatively high vapor pressure.

Going over a few bumps could cause pressure in the tank.

Try driving on a smooth road for a mile or so then check for pressure.

Do you pump your own gas?

I sometimes hear a pressure release when fueling up.

I would look at the carbon canister and hoses to it. It sucks up fumes to from the gas tank and burns them.

It seems a clogged fuel return line would create LESS pressure in the tank. You would also have other symptoms as your fuel pressure would be Way Too high at the fuel rail.
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Paul NW Indiana '90 745 turbo 145 K

I guess it means your cap seal is good at least!!

Again what would cause the rubber connecting hose to collapse?

Maybe a return hose clogged or collapsed??

I have noticed that my FPR hose is crimped where do I go from here? I appreciate your post.