Very odd..

Everytime I remove my gas cap to fill up, it goes PPPPPSSSSHHHHHHHHHHHH as it sounds like a lot of pressure is leaving the gas tank...

What is this? is it normal? What do I check for?

I think the gas cap is suppose to have a pressure relief valve built in. Yours may be bad?

Speed_racer said:

. . . PPPPPSSSSHHHHHHHHHHHH . . . What is this? is it normal? What do I check for?

Click to expand...

you may wanna check the vapor line from your tank and the vapor separator valve (ususally on/near the tank-end of that hose) -- the Cap is vacuum vented (vacuum will pass) but not pressure venting - that fuel vapor is supposed to route forward through your canister where the HCs will be retained in the charcoal media to (eventually) be readmitted to the combustion/emissions cycle -- could also be that your canister is fouled -- a quick check is to find a situation that would normally produce your pressure, then disconnect the tank's vent line at the canister and listen for the hiss there -- if it hisses, then the canister is fouled and replacing it is an option --

If the tank were (heaven help us all) allowed to vent pressure the EPA feels like it'd be an open evoporative pool of world-killing Hydrocarbons -- so they've required that fuel storage vapors be collected for "processing" instead of being released...

With all that said - the typical canister usually can NOT keep-up with the flow produced by a heated fuel supply (you do circulate about a gallon/minute through your fuel rail directly above the exhaust manifold... AND the tank does pick-up quite a bit of under-XJ heat from the exhaust systemsand all the rest) - granted, it will after time allow that pressure to vent through the media, or at least hold the fumes until everything cools back off and re-contracts... So a little hissing is "normal" when opening a hot tank, but if this happens after a short run on a failry cool tank, something else (like the valve, canister, or a blocked vent hose) should be suspected...

you dont have a vented gas cap... no big deal, just go to autozone and get a vented one....