Mercedes-Benz W212 CDI injector faults on the OM651 engine
W212 OM651: how can a faulty injector be recognised?
Symptoms are knocking, smoking, the engine warning light, and uneven running at idle and under acceleration. There are many symptoms and causes, so a symptom alone is not enough. A faulty injector is a common cause, and at worst it can break a piston and cause cylinder damage.
How is a leaking injector found on the W212 OM651?
Leak-off measurement and the injectors' electrical correction values on the diagnostic tool are part of the investigation. If the correction values do not even out the differences between cylinders, the instruction is to replace the injector. A leak-off measurement done without a diagnostic tool can miss a faulty injector if the fault only shows at a certain rail pressure.
Is replacing one injector enough on the W212 OM651?
Not always. Uneven running can continue because the other injectors may also be faulty, and in some cars all the injectors had to be replaced before the running evened out. Used injectors should not be fitted. A wrong injector type can cause black smoke, so the type must match the engine.