Following the 1988 season Guerrero and Granatelli split for 1989. Guerrero joined Alex Morales Motorsports, who was at the time the factory (and only) team using Alfa Romeo engines. Guerrero drove the No. 21 Alfa Romeo March 89CE-Alfa Romeo Indy V8. The engine ended up being not ready for the start of the season and the team missed the first four races of the year, including the Indianapolis 500. Guerrero was even offered to drive an extra car for Truesports. Guerrero had to decline due to his contract with Alfa Romeo. The team managed to first compete at the Valvoline Detroit Grand Prix on the Streets of Detroit. In the race Guerrero was able to finish 8th. The remainder of the season saw Guerrero score only one additional point due to a 12th-place finish at the Red Roof Inns 200 at Mid-Ohio Sports Car Course. Guerrero would finish 23rd in points with 6 points.