There is a calibration code on the drivers door for the correct computer if you still have the original door...9 different ecm's for 1990 model year. The wrong one won't work
Google ACE Automotive Computer Exchange in Davie, Florida. They have rebuilt two ecm's for me. about 150 and it will be done right the first time.
1990 F150 Lariat 300 5 speed 3.55 ls C824's upgrade F250 3 inch leaf upgrade Centerforce II 11in clutch
silence is golden...duct tape is silver!