Gas tank pressure issue....??????

[wrd1972]

Hi, evry time I drive my 1995 z28 lt1 mostly stock, and then park it in the garage and shut off the engine I can hear this hissing and whining sound coming from my gas cap. It can last for sometimes a couple of hours. If I remove the gas cap a huge rush of vapors and wind jets from the gas tank. Is this normal or is there a problem with my car.
Thanx for all input.
Bill

[Joe 1320]

It is normal... however, you should make sure your existing cap doesn't leak.

[Injuneer]

It is normal for the tank to be under pressure. That is the way the vapor recovery system (EEC canister) is designed to work. However, excessive pressure buildup could be the sign of a problem. A couple of possibilities....

-the fuel pump is wearing out and the excess heat it generates is heating the fuel and generating more vapor and more pressure in the tank.

-the pressure relief valve on the EEC canister system is not functioning properly, and holding too high a pressure in the tank.

-the carbon in the cannister has "collapsed" and is blocking flow, or the canister is saturated with fuel and vapors can't get through. This will generally cause the pressure relief valve to realease pressure.

Are you sure the sound is actually coming from the cap? Could it just be noise from the canister, which is inside the fender, very close to the cap?

[wrd1972]

I guess it could be coming from anywhere in that general area around the cap. I just know that when you remove the cap the pressure is released and the sound is gone. How do I really know if there is a problem with one of the above scenerios, will I get a code or somthing.

Thanx
Bill