This is a follow-up to the msg with the above thread posted sometime back. I was experiencing engine pings which only occurs past 4,000 rpm. As suggested by one of the members here, it turns out to be the Bosch Platinum +4 plugs that I have recently changed to. A swap back to the standard Bosch copper plugs cured the engine pings. Strangely, the plugs were highly recommended by my local parts distributor. There were many positive feedbacks from users (same model & engine). Are there any users here who are happy with their Bosch Platinum +4s? I do notice that the engine has better response with the +4s, despite of the engine pings. BTW, anyone tried the Nippon Denso Iridiums on their Mercs? Feedback?