Fuel Jettison

[ourtomtom]

'95 C Class 220. On startup after standing for a day or two. Fuel can be seen to issue from an open pipe, adjacent to fuel pump. After a while it ceases, and doesn't manifest itself until the vehicle is left standing again - very puzzling.

I've owned this vehicle for 12yrs I did replace the fuel filter back then. When I had an issue with the Engine Management Unit which I eventually resolved. But I can't figure what is going on here.

I've seen this before and yesterday I noticed it had occurred again. So I removed the plastic cover over the filter/pump assembly and noticed an open pipe. Which presumably has been there for as long as I've owned the vehicle. I feel it should surely be connected somewhere to return this overspill into the fuel system. but there's nothing obvious, as to where it should go. Fuel issues from this pipe, but then it stops and only seems to occur after standing for a few days.

Any ideas?

Tom

 

[hotrodder]

Off the top of my head the only thing that makes sense is that the open pipe is part of the fuel EVAP/tank venting system... how much fuel are we talking and do you recall if it only happens when the car's been parked up after filling the tank?

Pic nicked from the internet showing the layout of the fuel EVAP system for a w202...

I dunno if all w202s got a fuel expansion resevoir* but they'll be at least two vent lines regardless; one for the EVAP system to deal with evaporative loses/pressure due to thermal expansion & vacuum as fuel is used and another to allow air/vapours out of the tank when refuelling which is typically larger diameter

Fairly unlikely (at least you'd hope!) but there's an outside chance that someone bodged things on purpose if there was something wrong with the EVAP system... trying to resolve things like the tank pulling a vacuum due to blocked breather valves or thinking that something was wrong with it as they didn't realise the system is designed to allow the fuel tank to become slightly pressurised

* sometimes the tank has an elaborate baffle system inside the tank to try and keep liquid fuel out of the vent lines in which case the filling vent goes from the filler neck directly into the tank and you have one other vent line for the EVAP system. This is how it was done on the 124, 129 & 140 where only the later got a seperate expansion vessel with a through loading back seat due to the shape the fuel tank needed to be to accomodate this (kinda like the saddle tank in the pic which is shaped for the propshaft to pass)... http://www.w124performance.com/service/w124CD1/Program/Engine/LHIS/47-0030.pdf