There were several attempts to re-engine the aircraft with the engine it was originally designed for, the Mikulin AM-37. This was designated the MiG-7, and one MiG-3 was converted to evaluate the engine in May 1941. It proved to have poor longitudinal stability and the powerplant itself still had a number of problems. The German invasion the following month caused the cancellation of the development of the AM-37 as Mikulin's resources were required for the AM-35 and AM-38 engines already in production.