my car has been running rough lately, but i noticed that every time i fill the car completely up with gas, it runs much much better. and also when i unscrew the gascap there is a loud and long hissing noise. my dad told me it might be a clogged gas tank vent. could that be so? and if so, would that cause the car to get leaner and leaner as the tank emptied? thanks to all in advance.

PS- i always fill uponce i get to 1/2 tank.

 

The noise you hear is normal. The first thing I would suggest is to change the fuel filter. My guess is you never done it.

 

Like he said, also gas caps are vented one way, to let air into the tank, not out.

 

thanks guys, i guess im going to replace my fuel filter this week, since im going to be changing the oil anyways.

 

So your saying it ISNT supposed to hiss?

 

What I was trying to say is that the gas cap is only vented one way. It is vented to let air in the tank as thegasoline is used up. It is not vented to let the gasoline fumes out of the tank, that is the job of the EVAP system. As the fuel in the tank evaporates it builds up pressure. This causes a hissing noisewhen the gas cap is removed and the pressurized fumes escape. Lessfuelin the tank, the more roomis available forpressurized fumes to collect, so an empty tank will hiss more than a full one, depending on how recently the EVAP purged the fumes.

 

ok kuz when i go to fill up around 1/4 tank it hisses.

 

That is normal. Just don't light any matches when you remove the gas cap. LOL

 

damn... i usually light a cigarette while i pump my gas.. guess i shouldnt do that anymore..