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While accelerating from a toll booth about halfway through my recent 500-mile trip from Pittsburgh to Chicago, I experienced a sudden drop in power. Immediately the engine reverted to limp mode (engine trouble light on) after which I took the next exit and called M-B roadside service. I was instructed to shut down the engine and hold for a few minutes until a technician was consulted. The technician recommended that I restart the engine and asked if the engine light cleared. The light did clear, and the engine idled smoothly. I was then told that I could continue my trip and have a dealer check the engine at my convenience – that is, if I would be comfortable doing that, having been told that no engine damage did or would result – or I could proceed to the nearest dealer a few miles away in Fort Wayne, Indiana. Well, I continued on without trouble and scheduled a service visit in Chicago for the next day.

The Chicago dealer spent 2 hours pulling the codes and troubleshooting. The codes revealed a misfire on cylinder #1, but no cause was verified. They ran a compression test; checked high pressure fuel circuit and ignition voltage/pattern; removed and checked #1 plug insulator, electrode, and gap; and test drove on highway at high speed. All was good. VERDICT: Unknown cause, possibly a slight water contamination of E10 fuel. The #1 cylinder at the end of the fuel rail is considered to be more susceptible to misfires from water contamination.