Diesel smell inside Movano 1.9 DTI caused by a leaking injector seal

A smell of diesel inside the cab that becomes stronger with the ventilation switched on and after a longer journey indicates a leaking injector seal on the 1.9 DTI. A worn fire seal, the copper sealing washer beneath the injector, allows combustion gases to escape into the engine bay and then travel straight into the vehicle through the fresh-air intake. The symptoms also include uneven idling and a rhythmic tapping noise from the top of the engine. Removing the rocker cover reveals a black, tar-like deposit around the base of the injector.

Why should the repair not be delayed?

Escaping combustion gases act like a blowtorch on the injector seat in the cylinder head and gradually burn away its sealing face. The longer the blow-by continues, the more difficult and expensive the repair becomes. The correct repair includes new injector fire seals, never reused even when they look serviceable, new O-rings, cleaning the injector seats and checking the tightening of the injector clamps. It is also worth replacing the fuel leak-off pipes. Their plastic connectors age at the same rate and are a frequent source of air entering the fuel system.