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Old 08-19-2009, 03:54 PM   #1
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Join Date: Jan 2006
Location: SF Bay Area
Posts: 6
fuel vent howl - fix it or just "bandaid" it?

2000 Boxster S has been making a noise similar to the flute-like sound you get by blowing over the mouth of a bottle. You could also call it a howl. Never could track it down, it would always come on while driving, all I could tell was it might be on the right side of the car.

Lately the howl got worse, it's on nearly all the time. Then the last two times I put gas in the car, it wouldn't start for a few minutes, and then only after a long time cranking. Never had any problems before.

This time when I put gas it, so as not to get stranded, I left the car running while filling up the tank. When I removed the nozzle, the howl/flute noise came on nice and loud, sure enough it comes from an opening behind the gas cap hinge. Experimenting, I could make the howl come and go by pushing the fuel filler throat flap open with my finger. Flap open, no howl. Flap close, howl.

So the noise is from the fuel venting system, like some other posters here have found. This system does not seem very simple, with electronically controlled valves. One of the posters paid more than $500 to have it fixed. Ouch.

Another poster made the noise go away by pushing a sponge into the vent tube to reduce airflow. This "bandaid" made the noise go away, but the underlying problem is still there, the venting system probably isn't working properly.

So, finally, here is my question: what bad things could happen if I don't fix this properly? Is the howl from air being drawn into the gas tank as fuel is sucked out? Is there an air filter on the intake? Maybe that filter is blocked, so that when the vent system turns on the valve to let air in, a vacuum is created that is pulling air in via some crack or something? Or maybe this vacuum is supposed to be used to draw air in from somewhere else?

Can someone point me to a diagram on the web somewhere showing the fuel venting system? I looked at Pelican but it was hard to figure it out.

Thanks in advance for your advice.

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