Teething Problems in the Debut of Mazda's Diesels at Daytona Three diesel-powered Mazda 6 racecars making their debuts at the Rolex 24 Hours of Daytona endurance contest all failed to finish. Each entry was sidelined by mechanical failure only hours into the twice-around-the-clock race, which began Saturday afternoon at Daytona International Speedway. Out of 56 starters, they were classified 53rd, 54th and 56th in the official results; they completed 51, 45 and 33 laps respectively, compared with the race winner's 709 laps. John Doonan, Mazda North America's racing chief, said the culprit behind the failures was a 25-cent fuel line nut that apparently had vibrated loose. The fuel leaks starved the engines, resulting in the loss of cylinders in two cars. The third car avoided that terminal condition and was repaired, but it suffered a failure of the engine's rear main seal soon after it re-entered the race, Mr. Doonan said. The cars had been plagued with vibration problems so severe that the drivers were told to limit engine speeds well below their power peak. An expert in N.V.H. -- noise, vibration and harshness -- will investigate the problem and make a plan to correct it, Mr. Doonan said. The next race in the series is a month from now in Austin, Tex. Mr. Doonan said the team would have benefited from more preparation and testing time before the event. He added that one of the three cars had been completed just a week before the race. The Mazdas were competing in the new GX class at Daytona; that class will be reorganized into another formula before the 2014 season. But Mr. Doonan said whatever form the class ultimately takes, Mazda is committed to continued participation. Mazda is using the program to develop and showcase its new 2.2-liter four-cylinder Skyactiv diesel. More than half of the parts in the racecar engines are regular production items; it develops 400 horsepower and 450 pounds-feet of torque. The production engine, rated at 173 horsepower, will be available later this year in the Mazda 6 sedan.