gas cap pressure

I failed my gas cap pressure on my emmisions test. Does this mean i could have a leak in my tank somewhere? any advice would help. thanks

just get a new cap...they are supposed to be vented...maybe yours dosnt anymore...

does that mean the tank breaths when u take the cap off or it doesnt. mine breaths when my tank is almost MT and im goin to refill. Is that ok?

Mine breathes all the time.

try a new gas cap, cause here in ca they test the cap off the car which means it could only be a bad gas cap.

the tank breathes all the time, just seems like it does more when the tank is empty because more fumes build up.

so should i just not even worry about it then? i still passed my emissions with flying colours. just not the gas cap bs haha.

...um..my tank dose not breath when i take the cap off... it used to with the old cap, my auto shop teacher told me to get a new one...he said its vented and your not supposed to here the "breahing" when you take it off.

...um..my tank dose not breath when i take the cap off... it used to with the old cap, my auto shop teacher told me to get a new one...he said its vented and your not supposed to here the "breahing" when you take it off.

First off gas caps are vented but not in the way you think. They have a one way valve that will let vacuum in but they won't leave pressure out. This would be venting hydrocarbons to the atmosphere which is a no no in CA. We check the cap's by seeing if they hold a pressure.

Gas caps are apart of the evaporative system.

You just need to get a new gas cap.

Smoghog

ok, so if you take your cap off and you hear the hissing sound, that's a good thing?

cause i am reading this thread and i'm hearing opinions going both ways in this thread.

mine makes the hissing sound when i'm close to empty, but not when i'm near full. still the original (16 year old) cap too.

the hissing is good...gas evaporates. I've noticed that my MPG has gone way down when I have forgotten to secure the cap right.

Anyone have an extra gas cap they might want to donate since it's the holidays, lol.

Gas cap cost 4-7 bucks...

ok, so if you take your cap off and you hear the hissing sound, that's a good thing?

cause i am reading this thread and i'm hearing opinions going both ways in this thread.

mine makes the hissing sound when i'm close to empty, but not when i'm near full. still the original (16 year old) cap too.

Yes, It is normal. It will do it more when the tank is empty that full. It is the air that expands not the gas. This pressure is forcing the vapors to the carbon canister to be held there until your computer tell's it to purge the canister after the car is warm.

Just wait, there is going to be another test soon to the the car's evap system. by pressuring the gas tank to see if it holds the pressure build up. So $5 is a cheap way out. For now.

SH