I just got a call from a friend who has the straight six cylinder E320CDI; and he's getting a pinging in the engine almost like a spark knock in a gasoline engine.

The engine performance is A-OK, but the pinging has him worried. Dealer service can't fix it; and their only recommendation is to try another brand of diesel fuel and put in an additive, although they didn't say what additive to try.

Any thoughts on how to fix this?

__________________
1973 280SE 4.5 (Sold)
1984 LWB 280GE (Sold)
2000 G500 NMLE - "Deep Throat"
2007 ML320 CDI (Sold)
2010 Porsche Cayenne S Transsyberia TipTronic (Sold)
2010 Audi Q7 3.0 TDI (Sold and Sorely Missed)
2014 ML350 BTC
2015 Audi Q7 3.0 TDI (On Order)