I feel like they are putting off releasing the diesel version for the North American market because of the engine failures they've experienced while road racing them. I believe all 4 of their cars experienced the same failure and with the U.S. market being amongst the most conservative they don't want to tarnish their name by releasing it too early and want to iron out any bugs.
Nothing to do with their Mazda 6 Clean Diesel racing car, which, by the way, have won their last several races, as the Porsche Cayman that they've been up against has been having mechanical difficulties, too.
At the end of the last race on June 30th, Mazda was officially 1 point behind Porsche for the class they are competing against each other in.
Nope, the reason for the delay to the US market is two fold:
First off, not all of the US market actually has diesel fuel with the low enough sulfur content, which risks parts like the fuel pump, and injectors.
Second, they make way more money off of diesel sales in other markets, so if you can maximize profits, and decrease risk of fuel related failure, why rush the vehicles to a market that historically hates diesels?
Honestly, I would rather Mazda keep making huge profits in all their markets with the right mix of vehicles and engine sales, than to expose themselves to pointless risk for a small share of a small, problematic market.
BC.