Steps to Restoring Mercedez-Benz Engine Power
This bulletin applies to 2014 Mercedes-Benz CL550 4Matic vehicles equipped with the M278 engine. Misfire DTCs may be set in the ME engine control module. The engine may run rough, with poor fuel economy and a lack of power.
The engine also may be ticking while idling and during acceleration.
The complaint might be related to worn valve guide(s) in either cylinder head.
Perform compression and leak-down tests. Borescope the combustion chambers to observe any abnormalities in the cylinder or at valve areas. If it is determined that the complaint might be related to the cylinder head, remove the head to confirm it.
Check for elongated valve seats and inspect the valve guides. Repair or replace as needed. If abnormal wear relates to the left cylinder head, do not disassemble the head. Order a new cylinder head (left bank) complete with new valves, springs, camshafts, etc.