It seems to me this is where a vent solenoid would be attached. No such thing in this car it seems.

I'm not sure where this air intake valve is. The I can blow through the canister pretty easily. Can't imagine the nipple contained anything functional (e.g. a one-way valve). Still scratching my head here. Am I to assume that this is indeed the intended arrangement? There's just a short section of hose connected to the (now broken) nipple that just vents to atmosphere?

Starting to wonder if this is indeed the intended setup, and the canister is just saturated from years of the car sitting idle. It is kinda heavier than I would have expected. Regularly driving it would suck the HC's out of the charcoal filter. I'll get a new one on order in the meantime.

 

For what it is worth, the series 2, twinspark and 24v system, seem the same as your Q4. Both have the other canister under the front left wing. The diagram is misleading.

 

There are three vent pipes on the top of the fuel tank - assume these are the ones they mean (confusingly) rather than 3 pipes elsewhere. The front charcoal/thingy box I took off another car is in a shed and can't access it right now. Will take a look when can.
The fuel smell I got from my 24v was mostly from perished rubber vapour joints connecting to the blue plastic tubing.

 

Richard, great to know that those rubber joints are a source of problems! Mine look pretty good to me, but I will examine them closely if the new canister does not resolve the issue (which I just ordered on ricambinuovi.com - stoked). The Q4 does not have the three vent pipes on the tank, just the black one you see coming off the auxiliary level sender in the trunk (pic posted above), but yes, I interpreted the manual as you described.

Yeah, it would be interesting to see where that third port connects to on a regular 24V car. Feeling suspicious about the documentation!

Thanks

 

I just checked with Larry Dickman and he suggests there should probably be a one-way check valve connected to that port, to allow air into the tank, and not out. TBD. I can't find any documentation to that effect. I could imagine that that check valve might have been lost when the nipple broke. If anyone could set eyes on their tank, that would be cool

 

So I believe it's like my S4 Spider, in that there should be a port open to atmosphere on the carbon canister.

How it's supposed to work is that, when the car is parked, excess pressure in the tank vents to the carbon canister, where any fuel vapors are adsorbed by the carbon.

When you're driving, under certain conditions the ECU opens the purge solenoid to flush the carbon canister. This pulls fresh air in through the open port and desorbs the fuel from the carbon, which is then sucked into the engine to be burned.

 

Tom, thank you. Yeah, I just checked on my 916 spider and sure enough that port has a soft coupling to a rigid line that then just runs to the undercarriage and vents to atmosphere. And you confirmed the same. So I guess the broken nipple is no big deal. I suspect that the canister may just be saturated from years of trying to capture tank vapors and just no longer effective. It is possible that the issue would self-correct if I were to drive the car enough, or if I were to blast fresh air through there for while, but I'll toss the new one on and see what happens. Unclear whether that will address my offensive cabin odors if I crack the front window, but I'll take it one step at a time. Thanks a ton folks!