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So I took the S4 to get emissions tested today after a long spirited drive, and while I was waiting in line, I started hearing this intermittent 'groaning' type of noise coming from the back of the car. Approximately every 10-15 seconds, it would make this noise and then stop. After getting home and upon further examination, I traced the noise to a component in the trunk. (Pic is attached.) Even after turning the car off, the intermittent groaning noise continued for about 15 minutes. I didn't have time to remove it and inspect, but I thought maybe the experts could enlighten me. Any thoughts on what's going on in there? Thanks in advance!
 

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But Mad North-Northwest
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Were you telling any bad jokes? Perhaps the car is providing running commentary.

That's the tank venting system. There are two valves to the left of the big vapor tank. One is the white thing in the upper left: it's the valve that lets fuel vapor flow forwards to the engine compartment. The other is a one-way valve only connected on one side to let air into the tank as you use the fuel.

The valves have rubber diaphragms in them and can make some noise as vapor flows through them. The white one can be carefully pried apart and cleaned if you like, just note how it goes together and which direction it's hooked up. Cleaning it might help. Or you could just ignore it.
 

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from what i see, not see is the vapor tank venting thingy, it missing.. the lower vapor hose should have a vent one way valve then to the big black plastic box.. this allows the tannot to go into vacumum, as i this the sound you are hearing is the pressure trying to equalize.. i give it a try, from the tank vent a hose rises to the rear shelf buckhead, there there is a ' T ' conection, this is where the vent to air pressure equalize ( the lower part of the ' T ' is that yellow thing) you are missing that, this is a one way valve when the tank starts into vacumumn the yellow thing opens up a little to allow air to equalize the tank.
 

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But Mad North-Northwest
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Yeah, the yellow thing in Bianchi's pic is the second valve. I assumed it was off to the left of your picture, but if you don't actually have one that would be problematic.
 

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i took that picture in rise of my life;);)!!!! my car was in total darkness , only a wee 1 led bulb to guide my way,lots of saber toothed squirrels here:eek::eek::p:D
 

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Discussion Starter #6
Thanks for the info. I'm just seeing these replies and am at work, but will take a look when I get home. If I'm missing the 2nd valve, is it just a matter of placing one in line or am I also missing a vent line, as well? Thanks again.
 

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But Mad North-Northwest
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You'd need to tee it in, probably between the black overflow tank and the white valve at the top.

It would be odd if it's missing as those hoses and clamps look original. I'm wondering if Alfa stopped using the second valve in the later S4s? Only reason I say this is that it never seemed necessary to me: on the S4 the carbon canister is vented to atmosphere, and that white valve will actually let air flow both ways: it's designed to hold some pressure in the tank but opens easily the other way to let air into the tank.

All speculation on my part, though. Adding one definitely wouldn't hurt anything.
 

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Hmmm...I may be right. Check out this thread:

http://www.alfabb.com/bb/forums/spider-1966-up/18313-i-smell-gas.html

Post 80 is from a guy with a '92. He did not have the little yellow valve either. Also there are some pics of the setup with both valves if you're curious.
Thanks for all the insight so far, folks!

Gubi, very interesting read... maybe my car is indeed one of the few exceptions. I looked all around back there and everything appears to be in original, unmolested order with respect to the lines and connections. I need to next compare my cap with the description in that thread. I'm assuming based on feedback so far that the noise I'm hearing is indicative of the venting system doing its job, but is that a reasonable assumption? If so, I can live with it. FWIW, it was a very hot day and I was sitting in the car in the emissions testing line for a VERY long period of time when it started making noise.

Thanks again-
 

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But Mad North-Northwest
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Probably yes on the noise. As the pressure in the tank increases, it forces air forwards through that white valve which can make a humming noise. It's easy enough to pull off the valve and test it for function if you're concerned.
 
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