Gas Cap Question
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Joined: May 2011
Posts: 63
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From: Glen Burnie Md
Gas Cap Question
I stopped to get gas tonight and when I unscrewed the cap it made a huge gasping for air sound.I had used about 3/4 of a tank before stopping for this fill.Is this normal?........None of my other vehicles have ever done this,thanks
Le Mans Master
Joined: Aug 2005
Posts: 7,392
Likes: 216
From: Merritt Island, FL
Normal, especially when not much fuel left in the tank. However, it is also possible that you could have a problem with the charcoal canister and evaporative emissions system if it seems like an excessive amount of pressure in the tank.
Safety Car
Joined: Aug 2008
Posts: 4,344
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From: San Marcos CA
Just so long as the air is going in and not whooshing out. The excess pressure gets vented to the purge system which gets burned off in the engine- it's a one-way pressure valve. Both of my C4's I had did this. Apparently a slightly lower tank pressure develops on these models.
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Melting Slicks
Joined: Jan 2010
Posts: 2,024
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From: Austin TX
Just so long as the air is going in and not whooshing out. The excess pressure gets vented to the purge system which gets burned off in the engine- it's a one-way pressure valve. Both of my C4's I had did this. Apparently a slightly lower tank pressure develops on these models.
Safety Car
Joined: Aug 2008
Posts: 4,344
Likes: 48
From: San Marcos CA
If you ever pull the fuel line off and leave it hanging, temperature change will put a small pressure in your tank and push gasoline out the end of the line. I had to store my car with the cap off when I had the injection all taken apart.
Drifting
Joined: Jul 2006
Posts: 1,483
Likes: 3
From: Newark, New Jersey
actually it is vented. Thats what the charcoal canister is for. The purge control valve vents it to outside air. If you look under the canister theres a vacuum line that just vents to the outside
Safety Car
Joined: Aug 2008
Posts: 4,344
Likes: 48
From: San Marcos CA
Perhaps your car has been screwed with by bubba sometime in the past- it's supposed to be a closed system and when the engine is warm, the purge solenoid vents it to the intake manifold or throttle body to burn off the fumes thru the cats and out the pipe. Unburned gas fumes are 10 times worse than regular exhaust fumes...
If you ever have the chance to put an emissions analyzer next to an open can of gasoline, you'll see it peg off the charts for HC's- so much so that it is hard on the machine and could damage it.
you should fix yours, it doesn't rob HP.
Drifting
Joined: Jul 2006
Posts: 1,483
Likes: 3
From: Newark, New Jersey
The EPA may disagree with you.
Perhaps your car has been screwed with by bubba sometime in the past- it's supposed to be a closed system and when the engine is warm, the purge solenoid vents it to the intake manifold or throttle body to burn off the fumes thru the cats and out the pipe. Unburned gas fumes are 10 times worse than regular exhaust fumes...
If you ever have the chance to put an emissions analyzer next to an open can of gasoline, you'll see it peg off the charts for HC's- so much so that it is hard on the machine and could damage it.
you should fix yours, it doesn't rob HP.
Perhaps your car has been screwed with by bubba sometime in the past- it's supposed to be a closed system and when the engine is warm, the purge solenoid vents it to the intake manifold or throttle body to burn off the fumes thru the cats and out the pipe. Unburned gas fumes are 10 times worse than regular exhaust fumes...
If you ever have the chance to put an emissions analyzer next to an open can of gasoline, you'll see it peg off the charts for HC's- so much so that it is hard on the machine and could damage it.
you should fix yours, it doesn't rob HP.
Just checked. Even still had the print out the chevy dealer gave me about the routing of the lines. Its been a while. But youre right. It does vent to the intake. The vacuum line I was referring to that I initially said vented to the outside is actually the bottom of the charcoal canister fresh air intake
