I own a mercedes C 250D, its been running great so far. One morning it decided not to start, i detected an air leak into the fuel lines. After 2 days of diagnostics i was able to find a fuel leak at the joint between diesel pump and black plastic switch (not sure what this component is called).

Do i have to replace the whole pump or replacing the switch will solve the problem. Its the area marked in blue

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The black plastic valve is the shutoff valve. It is attached to the IP with two torx head bolts and has a nipple that inserts into the IP that has a simple oring which seals it to the IP. A new oring will solve the leak problem. That is usually all that is wrong with the shutoff valve. The oring is 2.5mm x 12mm ID x 17mm OD.

Its pretty simple to replace if you can reach it. Be gentle removing the electrical plug, it is part of the overall wiring harness and if it breaks you have to purchase the entire harne$$ to replace it. You dont even have to reove the other plastic fuel lines to do the oring.

Spray the trox bolt heads with cleaner so that your bit goes all the way in; some people have stripped them because of debris in the bolt head. It think the torque is 20nm? I know its not more than that.

The metal part further back is the "lift pump" (fuel pump) which uses suction to pull fuel up to the IP.

The line in red is the fuel return line that returns unused fuel back to the fuel tank.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Thanx for replying, guess will have to get my hands dirty. fingers crossed