Pressure from Gas Cap
 

I'm guessing somethings afoul with the evaporative recovery system on my car. Even in cold weather, when I open the cap to fill the tank, there's a noticeable rush of air.

Is this normal? I'm not getting any codes from the computer (assuming it's the LH-SFI computer I should be scanning).

Thanks

What vehicle? Most tanks should have some pressure in them to force the evaporative emissions out to the recovery unit.

the evap system has a valve which holds about 6-7psi [from evaporation due to heat from the sun] and it is quite normal to hear noise even in winter and especially when tank is heading to empty.

sorry - 92 300SE - but if pressure is normal - (I usually wait to fill up until I see the low-fuel light, so it takes 22 or so gallons) then I won't be concerned.