[pickwick]

I've been tracking my '92 coupe for about four years. Had a track day Saturday (72 degrees) and went out for gas mid-day. When I removed the gas cap air whooshed out for a full 30 seconds. I couldn't add fuel until it stopped or it would spit it back at me. At the end of the day I loosened the cap and had the same whoosh of air. Car ran fine before and after.



Never had this before. I'm not familiar with the valving of the evaporative canister system but it's all stock. What's going on?

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[Eric_K]

From having removed the stock filler & vent plumbing on my car, I can tell you the vent plumbing is quite elaborate on these cars. Aren't the caps vented? You might want to try a new cap before digging deeper.

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[rustech]

My understanding is that these cars and others are designed to have pressured fuel tanks when operating properly and if they don't, there's a problem. All of my cars give me a woosh when removing the cap, sometimes stronger than others. If you just open the cap all the way, it won't last 30 seconds. <img src="/forum/images/smilies/968/tongue.gif" class="smilie" alt="" />

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[Eric_K]

They definitely run just fine without any pressure in the tank.

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[pickwick]

[quote name='rustech' post='33260' date='Mar 26 2007, 12:14 PM']All of my cars give me a woosh when removing the cap, sometimes stronger than others. If you just open the cap all the way, it won't last 30 seconds. <img src="/forum/images/smilies/968/tongue.gif" class="smilie" alt="" />[/quote]



I'd never heard it before, and the 30 second whoosh was with the cap fully removed. Of course the little metal door for the nozzle is still there so there's still some restriction w/o the cap. I could understand 2-3 seconds, but 30 seconds worth must be a lot of pressure.

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[bob blackwell]

Yeah, I think the EPA requires capturing all of the emissions from the evaporating fuel in the tank. I know on some cars I have had a "check engine" light come on and discovered it is just the gas cap not firmly secured. Good luck, Bob Blackwell.

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[Chris Vais]

The governments air pollution regulations require that your fuel tank not be vented to the atmosphere, so when the cap is properly in place, it seals the tank. That is why you will get a check engine light if the fuel tank cap is not seated properly. So there will be a pressure build up in the tank and the car is designed to run OK with a pressurized tank.



The emissions control system on your car is designed to vent the tank periodically. It isn't a continuous thing and the venting takes place at certain engine rpm ranges so that the extra fuel vapor that is vented into the engine intake system doesn't result in excess hydrocarbons in the exhaust.



So if the car is sitting in full sun for a while and you remove the tank cap you may experience venting. I would bet that if you ran the car at something more than an idle, the tank would probably vent to the engine and you wouldn't experience the vent to the atmosphere. Every once in a while we experience this with both the 968 and our Audi A6 Avant although it is more likely to occur in the warmer months of the year.

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