I get injector knocking when I use ULSD, when I switched to bio injector knocking was gone. The engine is much quieter on non-ulsd/bio as well.

On ULSD I could definitely tell that my engine was on at idle, on BIO/non-ulsd I can't even tell if the engine is on, I have to keep looking at my tach to make sure. Its a HUGE difference.

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2005 SL65
1999 E300
1995 E300
1994 SL320
1988 560SL
1987 300TD
1982 300D
1955 300SL