Mercedes-Benz W203 CDI: injector return leak test and leaking injectors
Mercedes-Benz W203 CDI: how do you test the injector return leak and what is the limit?
The return lines are disconnected from the injectors and routed into separate containers, after which the engine is cranked or run briefly. The test is done on a cold engine. The leak of a single injector may be at most 20 ml/min, and the difference between injectors must not exceed 20 %.
Mercedes-Benz W203 CDI: what symptoms does a leaking injector cause?
A leaking injector can make cold starting difficult and make the idle hunt. One badly leaking injector can mask the others, so the test is repeated after replacement. Air leaks in the fuel lines can cause similar starting difficulty.
Mercedes-Benz W203 CDI: how do you fix a leaking injector?
Most often the fault is in the injector's Teflon seal and support ring, and replacing them helps. Less often the cause is inside the injector. The bottom washers are straightened or renewed and the mounting bolts are renewed. An old washer or dirt on the sealing surface can lift the injector, causing it to leak.
Mercedes-Benz W203 CDI: can the leak come from somewhere other than the injector?
Yes. If fuel seeps from the top of the injector, the cause can be the return line connector O-ring, whose surface has been cut. In that case a new O-ring is enough and the injector does not need to be replaced.