BBergman - Like Psfred mentioned, your timing is probably retarded. After trying the things on your list, plus a few others, (tire pressures, dragging brakes, checking for fuel return line leaks, and so on) I adjusted the timing. This was enough to give me a bit more power (0-100km went from 18 to 16 seconds) and sneak my mileage up to 24-25 U.S. from the 20-21 I was getting before all the adjustments. I'd still like to get it a bit higher, but I feel like I can live with 25. Also, up in Canada I imagine that you've got a pretty serious winter blend on your diesel, that definitely can drop the mpgs a mile or two.

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Tjohn

82 300 SD
77 450 SL (gone)