I have taken my 2008 BMW 750Li to the BMW Service Center 3 times for engine pinging problem during acceleration with negative results. Would you happen to have a fix for this? I have been using 91 octane from Shell or Chevron since I've owned the car. I've had this pinging / detonation noise coming from the egine during sudden acceleration since I bought the car in May 2010. The dealer preformed some sort of induction flush of the fuel system but it didn't help.