The 1991 Champion Spark Plug 400 was the 19th stock car race of the 1991 NASCAR Winston Cup Series season and the 23rd iteration of the event. The race was held on Sunday, August 18, 1991, before an audience of 90,000 in Brooklyn, Michigan, at Michigan International Speedway, a two-mile (3.2 km) moderate-banked D-shaped speedway. The race took the scheduled 200 laps to complete. In the final laps of the race, Wood Brothers Racing driver Dale Jarrett would mount a late-race charge against Robert Yates Racing driver Davey Allison, passing Allison in the final lap of the race and besting Allison by 8 inches (20 cm) at the finish to take his first career NASCAR Winston Cup Series victory and his only victory of the season.^[1][2][3][4] To fill out the top three, Penske Racing South driver Rusty Wallace would finish third.

The race was held at Michigan International Speedway, a two-mile (3.2 km) moderate-banked D-shaped speedway located in Brooklyn, Michigan. The track is used primarily for NASCAR events. It is known as a "sister track" to Texas World Speedway as MIS's oval design was a direct basis of TWS, with moderate modifications to the banking in the corners, and was used as the basis of Auto Club Speedway. The track is owned by International Speedway Corporation. Michigan International Speedway is recognized as one of motorsports' premier facilities because of its wide racing surface and high banking (by open-wheel standards; the 18-degree banking is modest by stock car standards).

Qualifying was split into two rounds. The first round was held on Friday, August 16, at 3:30 PM EST. Each driver would have one lap to set a time. During the first round, the top 20 drivers in the round would be guaranteed a starting spot in the race. If a driver was not able to guarantee a spot in the first round, they had the option to scrub their time from the first round and try and run a faster lap time in a second round qualifying run, held on Saturday, August 17, at 11:00 AM EST. As with the first round, each driver would have one lap to set a time. For this specific race, positions 21-40 would be decided on time,^[5] and depending on who needed it, a select amount of positions were given to cars who had not otherwise qualified but were high enough in owner's points; up to two were given. If needed, a past champion who did not qualify on either time or provisionals could use a champion's provisional, adding one more spot to the field.

Alan Kulwicki, driving for his own AK Racing team, would win the pole, setting a time of 41.515 and an average speed of 173.431 miles per hour (279.110 km/h) in the first round.^[6][7]

Donny Paul was the only driver to fail to qualify.