Prior to 1990 Morales Motorsports closed down and Patrick Racing took over the Alfa Romeo project with Guerrero driving the No. 20 Miller Genuine Draft March 90CA-Alfa Romeo Indy V8. Guerrero managed to qualify for the Indianapolis 500, starting 28th and finishing 23rd due to suspension damage. The team then switched to using a Lola T90/00 starting at the Marlboro 500 at Michigan International Speedway. In the race Guerrero finished in 5th place. At the end of the season Guerrero finished 16th in the points with 24 points.