1994 FORD MERCURY SABLE, won't give diagnostic codes

1994 FORD MERCURY SABLE, check engine light stay on and will not give out any diagnostic codes(had checked at 3 shops)fuel pump and fan run all the time when key is turn on.Will start only if gas peddle is not depressed. When running, engine stalls when depressing gas peddle more than just a little at a time. After running few minutes the catalytic converter or exhaust start to smoke a little and engine temp reads ok. shop says to start by buying new computer control module(F44F-12A650-FA )and hope that is whats is wrong.Can't find used computer control module around here.I've always been able to fix anything on our cars before. But last time I thought it was a computer control module I wasted $250 when the problem was in the distributor. :crying: