Dale Earnhardt Jr. will move to the back of the field for the start of his Budweiser Duel on Thursday after an engine failure in Wednesday's practice session.
The Hendrick Chevrolet driver had secured sixth on the grid for his Duel, which will decide the starting order for Sunday's main race.
"I'm sure there is some logical explanation as to what happened," Earnhardt said, "but we'll just put a new one in and start at the back of the qualifier and race up through there."
Reigning NASCAR Sprint Cup champion Brad Keselowski suffered a less serious delay when a fuel pump problem on his Penske Ford sidelined him for some of first practice.
The main incident of the day was a tangle between Carl Edwards and Ryan Newman. Both felt it was a symptom of the new Gen-6 car's different behavior in drafting packs.
"I didn't know what happened, and he honestly admitted that he didn't know what happened," Edwards said. "Just all of a sudden, my car was going across his nose. It was just something new, and a different characteristic of this car, I guess."
Michael Waltrip was fastest in practice one for the revamped Swan Racing team, with Hendrick's Kasey Kahne leading the later session.