Mercedes Diesel Injector Seal Repair

Mercedes four-cylinder CDI diesels — including the OM646 and the 2.1 litre OM651 in the C-Class, E-Class, Sprinter and Vito — are known for injector seals that leak. The injector sits in a copper washer; when that seal fails, combustion gas escapes past it with a ticking or chuffing sound. Over time the gas and oil bake into a thick black crust around the injector, which is why mechanics call it the "black death".

Left alone, the carbon welds the injector into the cylinder head. What should have been a simple seal replacement turns into hours of extraction work, sometimes a damaged head. There is also a diesel or exhaust smell in the cabin, and on some cars rough running.

Early OM651 engines, built roughly from 2009 to 2011, had Delphi piezo injectors that were subject to a recall and are prone to failure. If your car has those, we check whether the updated injectors have been fitted and test the injectors while they are out.

Our repair removes the injectors, cleans out every trace of carbon, fits new washers, seals and hold-down bolts, and checks the injector return and leak-off before rebuilding. We give you a quote before starting and tell you if an injector is seized so there are no surprises.