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E39 M5 Fuel Pipes

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My understanding is that there are 3 lines/pipes related to fuel running the length of the car


I believe that the outer most (ie towards the sill) 3rd pipe is the breather?


And forgive my ignorance but therefore it carries no fuel?


If thats the case why would there be a line/pipe running the whole length of the car? Surely there would just be a short breather routed somewhere else?


Can anyone share their superior knowledge? (it wont be hard to be superior in this instance! :-) )





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It's to do with emission control.


The third (vapour) line carries the excess fuel vapour from the fuel tank up to whats known as a charcoal canister which is usually located in the engine bay. 


This canister reduces the hydrocarbon content of the fuel vapour with any excess drawn off and piped to the engine to be burnt during normal combustion. 


This (long time mandatory) set up avoids the hydrocarbon pollution of fuel tanks vented direct to atmosphere, though vapour escape whilst refuelling is for the most part unavoidable.



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