Jimmie Johnson missed 45 minutes of the second practice Saturday morning at Michigan International Speedway as the No. 48 Hendrick Motorsports crew changed engines on the points leader's car.
"The guys saw something in warm up this morning, and we were trying to sort through it before practice started," Johnson said. "They took a deeper look at things right before practice started and decided to change it. We probably could have run some of this practice, but I think we had to change the engine regardless, but we didn't want to oil the track or create an issue and crash our car."
Johnson made three laps on his first run with a top speed of 195.122 mph during the second practice session. He made a second two-lap run just before the end of practice.
He returned for Saturday's second practice and ran 26 laps, posting the session's No. 2 speed behind Greg Biffle.
Due to the engine change, Johnson will have to start from the back of the field on Sunday.
Johnson has never won at Michigan. The team also changed engines on the No. 48 Chevrolet in June and finished fifth.