Mercedes-Benz W203 CDI: air in the fuel system
Mercedes-Benz W203 CDI will not start or stalls immediately: can air in the fuel be the cause?
Yes. The most common cause is hardened O-rings (round sealing rings) on the ends of the fuel lines, which let air into the low-pressure side. Symptoms are long cranking, starting only for a moment and uneven running.
Mercedes-Benz W203 CDI: where does air get into the fuel line and what should be replaced?
Leak points are the O-rings at the connections of the fuel filter, transfer pump, high-pressure pump and common rail pipe, as well as the rings under the pump cover. If the hoses are intact, replacing the O-rings is enough. The hoses are worth renewing if they fall apart when removed.
Mercedes-Benz W203 CDI: how do you bleed the fuel system after replacing the O-rings?
1. Fill the fuel filter with diesel before installing it. 2. Make sure the battery is fully charged. 3. Loosen the high-pressure side line connection and crank the engine until fuel comes out without air. 4. Tighten the connection and start the engine. If the engine does not start, check that the hoses are in their correct places.