What is considered "high sulphur"? How many ppm? How many ppm should a 7.3IDI have to be considered safe fuel for this engine?
S15 (ULSD) is defined by the U.S. Environmental Protection Agency (EPA) as U.S. diesel fuel with a sulfur content not to exceed 15 ppm (parts per million). S15, S500, and S5000 are designations for diesel fuels that meet 15 ppm, 500 ppm, and 5,000 ppm maximum sulfur content, respectively, as defined in the American Society for Testing and Materials (ASTM) standard D975 Table 1. In different regions of the world ULSD may refer to different maximum sulfur content values, but ULSD and S15 are often used interchangeably in North America (U.S. and Canada).The S15, S500, and S5000 designations also apply to the Canadian diesel market.
When is S15 (ULSD) required to be produced and sold?
Introduction of the new 15ppm diesel into different portions of the diesel fuel supply channel will be managed through staggered compliance dates. For North America, there are currently three S15 (ULSD) implementation timelines.
United States (except California)
On-Highway Diesel Fuel
Refinery < 15ppm by June 1, 2006
Terminal < 15ppm by September 1, 2006
Retail < 15ppm by October 15, 2006
Off-Road / Locomotive & Marine Fuel < 500ppm by June 1, 2007
Now back to your question on what is good for the 7.3?
I would run a biodiesel mix of 5% to make up for the lack of sulphur