The most famous OM646 affliction is leaking injectors, often called the "Black Death" or "Dieselkriechen" (diesel creeping). Over time, the copper sealing washers at the base of the injectors can fail. This allows combustion gases and unburnt fuel to escape past the injector, creating a hard, black, tar-like deposit around the injector. Symptoms include a strong diesel smell in the cabin, a knocking or "nailing" sound from the engine bay, and if left unchecked, can lead to seized injectors or damaged cylinder head threads.
While the OM646 uses a robust duplex chain, it can stretch over 200,000+ miles. The manual outlines the timing marks and tensioner replacement procedures.
Diesel leaking past the copper injector seals leads to "black death" (carbon buildup). The manual provides:
Rotate the crankshaft clockwise using a 27mm socket on the harmonic balancer pulley bolt.
The OM646 utilizes a duplex timing chain located at the front of the engine. Unlike rear-timed modern engines, servicing this is highly accessible but requires strict alignment.
Charge pressure control malfunction (Too low or too high boost pressure; check for cracked intercooler hoses or a sticky VGT actuator).
Glow plug failure on Cylinder 1 (Check glow plug resistance or the glow plug control module).
Vital for extracting seized injectors without cracking the valve cover.
The Exhaust Gas Recirculation valve is choked with carbon. Remove the EGR valve, clean it with heavy-duty carb cleaner, ensure the mechanical valve snaps shut freely, and reinstall.
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