Despite years of research and potentially billions of dollars, Mazda has yet to introduce its SKYACTIV-D turbodiesel engine on North American soil. And, according to a story at The Truth About Cars, it still won’t arrive anytime soon.

According to an unnamed source close to the situation, it appears that the latest delay is so Mazda can incorporate an unspecified exhaust after-treatment system. The original diesel didn’t offer one, but the company couldn’t get it to hit both the strict U.S. emission standards for diesels while still offering the performance and efficiency that customers will demand.

SEE ALSO: North American Mazda6 Diesel Delayed

The first Mazda6 diesel is expected to be offered in about a year’s time, with other SKYACTIV-D variants of the CX-5 SUV and Mazda3 compact hinging on public acceptance and sales.

In other markets, the 2.2-liter turbodiesel produces 170 and 310 pounds-feet of torque, both significant improvements over the older engines found in the Volkswagen Passat.