OK so not a total mystery but in rebuilding fuel system and also 'rationalising' what is installed I came across this hiding up out of sight at the top right side of the tank, close to the evap canister to which it also connects. It has a vacuum hose connected that is on a 'T' from the ECU, there is a pipe to the Evap canister shown in the last image, there is a rubber hose and metal pipe headed of down the rear of the back seat - I have no clue where it goes - there is no evidence of it in the engine bay - guess I need to do some real Sherlock Holmes on it

Starting with the parts books and ..... there is no evidence for such a thing .... now I get that it is some sort of closed loop evap purge but what is to stop fuel getting drawn into this - is it a vacuum controlled switch or something vacuum regulated - and why wouldn't fuel be pulled through it not just vapour.

I think it is a Rochester valve - part ID CBC7714 but such a part is not listed for my car - perhaps a recall. According to Kirby Palm's reference it is a switch but it still doesn't explain 'how' it vents the tank, perhaps it is open to atmosphere and allows air in as long as there is a vacuum - guessing it could be fun if the vacuum were able through some defect to draw fuel through it - that would mess up the emissions for sure. I think it time to have a real hard look at the vapour management on the car and just how to vent the tank appropriately.

Which is the next question - the vapour canister has four connections, the tank has three - does it matter which pipe goes where because I can't find that detail either. There is nothing on the canister to identify any particular function, and if it doesn't matter why the hell are there three ports on the tank - unless it is to pull air from three different sections of the tank that are closed at the top. I'm not going to take everything apart to put the camera in there again. I should volunteer for an idiot award as I tried to fit the level sender with two seals because I didn't pick up on the one that was stuck in the tank - took me 20 minutes to figure that one out.

And yes when I bought new fuel hose I didn't consider these suckers .... guess that is idiot award two .... I hope the hose headed toward the back seat and the metal line doesn't need fuel grade line because no way is that replaceable without pulling the tank - or perhaps the back seat. I am replacing the vacuum hose front to back.





The strange device goes to the port lurking at the back of the canister in this image.

 

Ben.
That is indeed the Rochester valve, all UK spec pre facelifts had them.
This is what I did and I strongly suggest you do the same.

• Ditch the canister
• Make sure the RV is working. It should let vapour out to the outside with no effort needed, and should let air into the tank with slight vac applied. This vac is supplied by the engine runnig and is a takeoff from the ECU vac signal that rus under the car from the crosspipe. They do jam, just pop the top off and clean it up if yours has.
• Send ONE tube from the tank to the RV and block off the other two. 20 years now of no smells and no problems.

The breather tube, as you probably know, runs from the RV along the back bottom of the tank space and out to atmosphere just in front of the rear wheels. Worth blowing it through/ poking the under car end to ensure it is free.

 

It shall be done, it seems that even as a 'fix' (which is how Kirby describes it) it didn't work, that's one task for the weekend, getting close to buttoned up on the fuel system - still not too happy with the threaded portions in the tank but the Hylomar and Loctite 577 are here so they will be forever sealed later in the week - hoses will be replaceable without messing around with 'crimps' ....