The ability to cycle the glow plugs during cranking/while running to prevent stumbling starts and mass quantities of blue/white smoke.

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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground.
1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers.
1986 Mercedes-Benz 300D - Sold, Euro non-turbo car.