Pemex consistency is anything but. REGULAR diesel varies from 240-400 ppm azufre depending on the refinery, whether or not it had suffered a process "upset" and from whatever source the crude oil came from. Heavy sour Maya crude yields a significantly higher azufre count than (recently arranged) fracked crude imported from the USA.
I refrain from commenting which fuel is suitable for which vehicle because I am in the dark just like mos folks. But I do know refinery processing capability. Bob Kennedy and I raided the shut down Shell Oil Platformer unit of fifteen or so dictionary thick hard cover volumes of Bechtel and Fluor engineering data of refinery design. In our spare time (different shifts) we studied and commented on various refinery processes. There is a lot of information within the pages of 50+lbs of books. Hydrotreating, Catalytic cracking and feed treating, alkylation, and gasoline additives were of special interest.
Shell had a room in LOP control center with eight forty thousand dollar mini distillate testing machines. The sample process was automated to cover the 7 test points of boiling points. Everything from initial boiling point to end boiling point. Sampling occurred every shift, sometimes twice a shift. Results were taken upstairs to be evaluated and immediately reacted upon. This was 47 years ago. Luis and Guillermo were impressed because current Mexican refinery operations are devoid of such micromanagement.
Mexican refined Magna gasoline contains a significantly higher ppm of sulfur than any brand of US refined gasoline. This is why I chose to use only Premium which is USA refined. Use of premium eliminates the need for periodic dosing with Chevron Techron. If you want to see a motor vehicle stall and run like a piece of ----, look at my toad after six months use of Mexican refined Magna. When traveling in Baja California the state, I use Magna because it is USA refined. Some cars could care less. I wish my toad could use cheaper Mexican Magna.
(Guesswork) One of the ways Pemex could jump a lot of hurdles is to "require" non Pemex (new) gasolineras in DF to carry UBA Diesel. Using "Pigs" in pipelines to separate fuel, USA refined UBA diesel could be piped from Veracruz to Mexico and Mexico edo. This in itself is going to be a big job for Pemex and by controlling pipeline flows from adjacent refinaciones a reasonable assurance is assumed that the city and state will get only UBA. (End of guesswork)
Something has to be done. Pemex is trying to direct a changeover so that the city and state offers only UBA diesel and UBA gasoline. They have their work cut out for them. I wish them all the good fortune in the world. Breathing Stage II DF smog alert air would make a believer out of anyone.