Mazda has officially delayed the U.S. market release of its highly-anticipated Skyactiv diesel engine for the second time, according to a press release.

Mazda said in a statement issued on Jan. 9 that the debut of its Skyactiv-D clean diesel engine in the U.S. is "being further delayed from its spring 2014 announced debut timing."

Originally the new engine was slated to launch in the 2014 Mazda 6, but now the Japanese automaker can no longer confirm it will be ready in time to launch with the new vehicle.

"I know there are a lot of questions, but I can't say at this point that it will be in the Mazda6," Jeremy Barnes said to Edmunds this week. "The delay has to do with matching the exhaust emissions to the engine's performance. We want the car to drive like we want it to drive."

Mazda was hoping to equip the new Mazda 6 with the Skyactiv diesel engine to meet demanding U.S. emissions requirements without the extra cost of an exhaust after-treatment system, according to the automaker.

"It was decided that further development is required to deliver the right balance between fuel economy and Mazda-appropriate driving performance," Mazda said in its statement.

Specifications, fuel economy expectations and pricing information were not made available by Mazda in the press release however.

The first delay occurred due to certification issues and final emissions testing.

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