Mr Benzfan,

This is very interesting. I have had my 98 C230 for 1 year and it has always had a knocking problem. I called the dealer and they said to use regular. No kidding, they said this was recommended by "headquarters" for the M111 engine. For the last year I have tried every different octane and every different brand and none of it made any difference. I changed out the cat and that did remove a secondary "voluntary" rattling but the primary rattle is still there. I cannot swear it is knocking but it fits all the criteria of knocking, sounds like it and is load related. On the other hand I have a hard time believing that a piezo sensor could go bad. Should I just change out the sensor and cross my fingers?

Thanks,

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra