A few years ago, when the Nissan K21/K25 FI engines were coming onto the market,(and suffering from a lot of fuel quality problems), I had lengthily conversation with a factory engineer, who claimed that the refineries were adding some of the sulfur based compounds that were no longer allowed in the new formulation Diesel fuels into the LP gas. Or more succinctly, the sludge that they were extracting from the Diesel was being dumped in the LPG. I don't know if any of that was actually true, but knowing what I know about oil refining industry, it wouldn't surprise me at all if it is.

It also seems to me that in the past year or so there have been a lot fewer fuel system failures directly related to fuel quality problems in my region, so perhaps the LPG industry is working to solve the problem.