406 1.8 fuel tank pressurised ?

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fastandfurryous
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Post by fastandfurryous »

If you're still getting vacuum build up, then there has to be some blockage somewhere. I would suspect it's between the connection you've found, and the "free" end. Can you blow down this length?
ianb
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Post by ianb »

I,ve managed to find a diagram which shows the pipe from the elbow in the boot, running over the door frame and connecting to a cannister in the bonnet, this is the pipe that has air being sucked in from the boot end, however I think it's a generic diagram and its also in French which may be misleading.
Possibly this pipe is for drawing fumes away from the tank - not letting air in - I'm getting seriously confused at the moment- but thanks for feedback so far.
ianb
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Post by ianb »

Final summary, I've cleared all pipes I can find without actually dropping the fuel tank, all the pipes are now connected up but I still get suction in the tank, as a temporary solution I've replaced the fuel cap with a rubber emergency one, it's a good enough fit to stop petrol coming out but allows air to be drawn in - so I think I've just bypassed the 'air in' vent - it all seems ok at the moment unless anyone has dire warnings about this sort of 'fix'?
Thanks for all the feedback
pug_owner2002
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Post by pug_owner2002 »

I've heard that your car can fail an MOT if one of those emergeny caps is fitted.
Maybe someone could tell us if this is true?
ianb
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Post by ianb »

I think you're right about the mot - having said that I can't remember any mot tester looking at the petrol cap in all the years I've been running old(er) cars, - however this cap is only temporary until I can sort the problem out,
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fastandfurryous
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Post by fastandfurryous »

The diagram you have of the pipe going to the engine bay is of a system with a charcoal cannister to collect vapour from the fuel tank when the car is not in use. I have only a bit of experience with these, but there is usually some form of vacuum-driven valving arrangement to change from collecting vapour, to venting air across the charcoal, and opening the tank up to allow air in. This may be the next avenue of investigation.
The temporary fuel caps *should* fail the MOT, although some testers are hotter on this than others.
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