Fuel system tank pressure

[a.Lpha]

I've been doing some reading here and am now curious as to how much suction you all get out of your fuel tank when unscrewing the cap to refuel. I think I may need to check my valves because i get some serious suction.

 

[DNTOEARTHMAN]

suction or pressure

Are you sure it's not pressure instead of vacum? Caps are designed to minimize a vacum situation via a check valve.

 

[cribbj]

Toyota's philosophy to minimise vapor emissions from the fuel tank is to vent it periodically to the intake manifold via the charcoal canister and either a check valve or a VSV. If you're getting pressure out the cap on a hot day, or vacuum, then someone may have tried to bypass the charcoal canister, and/or the venting system isn't working.

This is actually one of the pollution control systems that works well and doesn't impact the engine's performance, so it's better to leave it alone. It also keeps your garage from smelling like a leaky lawnmower.