Vapour Trap, or what?

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What's this pipe for?

Last but-one fill up at the local CPC station was followed by a very strong (headache inducing) and persistent smell of petrol. Couldn't see a leak, and the subsequent top-up at the same place to establish post-carb-reconstruction consumption didn't repeat the smell, so I assume the kack-handed yoof just spilled a lot of petrol.

Self-service places are fairly rare locally, but I may have to start seeking them out.

Anyway, while looking for leaks, I noticed this open pipe.



It has apparently been connected to something in the past, because the end is stretched a bit, as by an insert, but I can't see anything it could have plugged onto.

Best guess is it was a connection to an activated charcoal vapour trap cannister, though theres no sign of one, or mountings for one, now.

The other part of this pipe is the middle of these three loops inside the car.



By coincidence, at the end of last semester, for no particular reason I took what might be a vapour trap cannister from the (empty) engine compartment of an abandoned Corolla on campus (wish now I'd taken its wheels and tyres before they towed it).

I suppose IF that's what it is I could hook it up to this mystery pipe somehow, though its got 3 connections. Or I could just put a filter or a golf tee/bolt in the mystery pipe and forget it. Its probably been open for a decade or so.

denso 77740-12520 138600-2650



Google seems to confirm its a vapour cannister, though from a quick look I didn't find that particular one.
 
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Charcoal canisters are a hydrocarbon "filter" for the petrol tank to vent through. then when you start the engine, the engine draws the vapours through to be combusted.

If you put a golf tee in it, you risk sucking the tank in (like Ford Lasers did in the 80s).

If the dill overfilled it badly, you could have had leakage through it.
 
Originally Posted By: Shannow
Charcoal canisters are a hydrocarbon "filter" for the petrol tank to vent through. then when you start the engine, the engine draws the vapours through to be combusted.

Or in the case of BMW 3-series as late as about 1995, vapours passed through the canister and seemingly straight to the atmosphere...

And yet, there is a vacuum line to the intake, a purge-valve and a line to the fuel tank, in addition to the "hose to nowhere" you can find underneath or read about online.

That theory seems the consensus on Bimmerforums. I feel there might be more to it, perhaps some "dulskuggery" in the canister itself that controls whether air goes to atmosphere, or perhaps uses an atmospheric intake to accomplish something with the charcoal?
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Originally Posted By: Shannow


If you put a golf tee in it, you risk sucking the tank in (like Ford Lasers did in the 80s).



Didn't think the suction would be that strong. Assumed it would kill the engine through fuel starvation first.

As I said, there doesn't seem to be a vapour trap in the system now. I suppose there could be one downstream, but I suspect there was one and its been removed sometime.

Thinking I'll either work out something with that Corolla cannister (which probably means looking into the setup on Corolla's) or I'll put a cheap scooter fuel filter on the end of the pipe.
 
Seems the more recent ones might have computer-controlled valving,
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a bit challenging on my car, though I do have an old laptop
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.

Might be able to disable that though, if I can establish what the three pipes on the cannister actually do.
 
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I appreciate anyone taking an effort to curb pollution, but in your case buying a new car would be a lot more effective.

The three lines look like tank (big one on the top), purge (small one on the top), and atmosphere (bottom). There needs to always be a path to the atmosphere so clean air can go in or out of the tank. The canister is supposed to adsorb any HC vapors that try to get out. Then, while the car is being driven, a flow of air goes in the bottom and out the purge line to the engine, where the vapors are burned.

Usually the purge is set up to only operate while the engine is warmed up, and being driven down the road at above idle speed. A cold engine and / or at idle speed tends to run badly with the extra air.

The vacuum line diagram under the hood should show how the purge is hooked up, if a canister was originally fitted.
 
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