Mercedes-Benz W202 diesel does not start or cranks for a long time – air in the fuel line
Why does the Mercedes-Benz W202 diesel crank for a long time or not start when there is air in the fuel line?
When air gets into the fuel line, the pump does not get fuel but sucks air. Starting takes longer, especially on a car that has stood overnight. Air bubbles visible in the clear fuel pipes indicate a sucking leak.
Where does air usually get into the Mercedes-Benz W202 fuel line?
The most common places are hardened O-rings at the fuel filter connections and the pump connections, and at the base of the shut-off valve. Brittle plastic hoses, loosened hose connections and a rusted tank pickup pipe can also leak. When the filter is replaced, a new leak can appear at the connection.
How can the air leak be found?
Watch the clear pipes with the engine running: no bubbles should be visible. The end of a hose can be put into a can and the car started, which reveals the bubbles. The leak can be tiny, and fuel does not necessarily leak out. A non-return valve alone does not usually cure the fault.
How do I bleed the fuel line after a filter change or an empty tank?
Fill the tank over half full so that enough fuel reaches the pump's suction side. Air collects at the highest point, in the filter's transparent pipe, from where it is worth removing. Fill the filter and pipes with a syringe and start the engine.