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.
Vehicle context: C 250, 2013. Chassis: C-Class W204 Sedan. The same warning may require a different diagnostic path on another engine or year.
Symptoms and customer complaints
Constant cylinder-3 misfire with P2307, P0303 and P0313.
Intermittent rough running/misfire that clears after key-off/restart; P0302, P0303 and P2336.
Constant cylinder-3 misfire with ignition-coil-C primary-circuit high fault.
Intermittent cylinders 2/3 misfire and cylinder-1 knock-threshold fault; temporary reset after restart.
Recorded trouble codes: P2307, P0303, P0313, P0302, P2336. A stored code points to a monitored condition, not automatically to a failed component.
Diagnostic approach
The researched cases used checks including Swap ignition coils; Swap spark plugs; Back-probe coil-connector voltage and ground. A technician must interpret the results in the context of the actual vehicle.
The recorded case findings included No change; misfire remained cylinder 3; Same as other coils key-on and running. These findings are examples, not assumptions to apply to every Mercedes-Benz.
Documented causes in the source cases included Failed ignition coil(s); exact quantity/cylinders replaced are not stated. Similar symptoms can result from other faults, so testing is needed before repair.
Reported successful case repairs included Repair/replace failed ignition coil(s). These are external research outcomes, not work claimed by our shop.
If you are experiencing similar symptoms, call Mich’s Foreign Cars in Hickory at 828-324-6012 with the vehicle year, engine, warning message and the conditions under which the problem occurs.