Pemex Diesel Fuel Update

1.
The emissions system used by vehicles designed for ULSD is not really a "bolt on". It is much more complicated than that. It involves an entire emissions programming set that monitors emissions and controls regeneration cycles, as well as fuel injection rates. Removing the system requires reprogramming of the ECM, which in itself is complicated and more easily done during manufacture than in an aftermarket environment.

2.
The emissions system doesn't remove the last 15ppm of sulfur. Sulfur compounds formed during combustion from this 15ppm are ignored by the emissions system and mostly pass out of the tailpipe. Anything above that concentration interferes with the functioning of the SCR (Selective Catalytic Reducer) which uses Diesel Exhaust Fluid (DEF) to reduce oxides of Nitrogen (NOX) in the exhaust. When higher sulfur fuels are used, sulfur compounds temporarily poison the catalyst surfaces until the next regeneration cycle burns the sulfur out of the system.

Sorry for my poor wording.

By "bolt on" I meant to say the basic engine block and a lot of the basics are the same whether the rig is built for US or Mexico. The emission equipment differences do not mean it is a different engine. It is the same basic engine with a lot of added equipment and sensors that can send messages to the ECM to control operation - probably more poor wording.

I meant to point out that having available 15ppm fuel is better than having only 500ppm fuel as far as clean air is concerned. 15ppm sulfur has 485 fewer ppm than 500ppm.

I recognized that a lot of this stuff is a lot more complicated. I am probably not qualified to make a more scientific explanation. Many readers probably don't understand the more scientific explanations any more than I do.