Combustion and misfire diagnosis
A cylinder-specific misfire may come from ignition, injector delivery, air leaks, compression loss or valve timing. Identify which cylinders misfire and under what load or temperature. Inspect ignition and fuel trims, test coils and plugs where appropriate, and use compression or leak-down tests when the fault remains in the same cylinder. On direct-injection engines, carbon deposits and fuel pressure should be evaluated when symptoms support them. Do not replace all coils or injectors solely because of a misfire code.
Repair decisions and verification
Verify smooth operation at idle and under safe load, monitor misfire counters and confirm that catalyst-damaging misfires are no longer present.
A V8-equipped E550, S550, CLS550 or GL/GLS may develop rough running, oil-use complaints or reduced power. These symptoms are not unique to the turbochargers.
How the problem should be evaluated
Assess ignition, fuel delivery, intake and charge-air plumbing, crankcase ventilation and mechanical condition. Confirm the source of oil loss rather than assuming a single gasket or turbo failure.
Why the model and engine matter: M278 component revisions and applications vary by year.
If you are experiencing this issue, contact Mich’s Foreign Cars in Hickory, NC at 828-324-6012. Provide the model, year, engine, warning text and when the symptoms occur so our service team can discuss an appropriate diagnostic visit.