Failure mode - Mercedes-Benz 2.1L Twin-Turbo Diesel (Sprinter 2014-2018)

Injector seal blow-by ('black death')

Reliability tier: aggregated - verify before ordering, see /disclosure/

Symptoms

chuffing/ticking noise at an injector under load (combustion gas escaping the bore)
black tar-like crust building around one or more injectors
diesel smell in the cabin, rough running as a seal worsens

Compare with the other causes of the same sign on this engine: ticking, knocking, rattle or whine (2 causes) · misfire, rough idle, hesitation or surging (3 causes)

Root cause

The copper sealing washer at the injector bore fails (or was installed wrong / reused), letting combustion gas blow past the injector and coke around it. Caught early this is a reseal job: clean the carbon, fit new seals and NEW stretch bolts. Run long enough and it eats the injector seat. The signature OM651 owner topic - multiple independent service write-ups and community threads describe the same failure and the same fix.

Diagnosis

listen at the valve cover with a hose/stethoscope per injector under load - the chuff points at the cylinder
inspect for black crust around each injector before pulling anything
on reseal: never reuse copper washers or hold-down bolts - new seals AND new stretch bolts

Fixes

injector reseal (seals + stretch bolts) or injector replacement where the seat is damaged ()

OM651 Injector Copper Seal (611-017-00-60)
injector - more than one option: OM651 Piezo Injector (651-070-30-87), OM651 Piezo Injector, exchange (651-070-29-87-64)

Prevalence

common