Mercedes-Benz W163 CDI injector leak-off

Typical symptoms are hard starting, especially when warm or in cold weather, and fuel pressure staying low. Sometimes the car stalls and the EPC light comes on when the accelerator is floored.

A leak-off test measures how much fuel from each injector flows back to the return line. A leaking injector stands out clearly from the others: at worst the measuring cup fills in a couple of seconds. The test and the repair are done by a workshop, because this is a high-pressure fuel system.

The leaking injector is replaced, and at the same time the injector seat and sealing surface are cleaned and the seal is renewed. Starting usually improves clearly. Before replacing an injector, keep in mind that an air leak in the fuel line or the seal of the pressure sensor can cause similar symptoms.