7 or 8 years ago - www.biodiesel.infopop.cc www.tdiclub.com - it was necessary for running homebrew biodiesel blends. This was when the sulfur in diesel fuel went from 500 ppm to 15, with the resulting loss in lubrication. Lots of things were affected like cold filter plug points and reports of 'problems' that were actually extra fuel efficiencies the computer didn't expect or other such things.
Though VW was leading the way in biodiesel use and research in Germany the U.S. dealerships had no knowledge and spoke against using biodiesel, necessitating the hacks.
To be nobody but yourself in a world which is doing its best, night and day, to make you everybody else means to fight the hardest battle which any human being can fight; and never stop fighting.
e. e. cummings
Call me flak-catcher.