How does the c350 cdi fuel system work ?

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BlueGriff

Member
Joined
Jan 2, 2012
Messages
30
Location
Wiltshire
Car
C350cdi sport estate
Underneath the the rear seat I find two Bosch items. On the right A 204 470 2294 which has two thick wires presumably power supply and two thin presumably level sensor. There are no externally visible pipes on this side. On the left is A 204 470 035 which has two thin wires and two pipes. The wires appear too thin to be power.


How does all this work ? Plainly fuel needs to balance somehow between the tank either side of the transmission tunnel but with no pipes coming off the side with the thicker wires I am puzzled as to what happens.


The tank is currently fairly full so can't remove the pumps to look inside


I am poking about here because engine light is on and I have error code 0290 which points to fuel pump however car seems to run OK. After clearing the code it returns immediately.
 
The pipe work to balance fuel level between the two sides of the saddle tank is internal and uses the venturi principle. Do an image search for 2044702294 and you'll find a bunch of pics of the 'fuel delivery module' showing a bunch of the plumbing

This sort of thing has been used by most cars for a good while even when the tank isn't saddle shaped as it's an easy way to continually fill the fuel pick up in the tank and prevent the pump from entraining air when playing 'reserve light roulette'. http://www.w124performance.com/service/w124CD1/Program/Engine/LHIS/47-0010.pdf explains how things were done around 20 years ago when the fuel pump was often mounted outside of the tank. These days it's more sophisticated using 'venturi jet pumps' powered either by fuel return lines or by a seperate circuit taken from the main pump. A google search for fuel tank venturi and/or fuel tank venturi jet pump will get a bunch of hits that go into more detail
 

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