Someone please help I have a 83 conv that had a 3.8 in it and I swapped out for a 5.0 HO out of a 86 grand marquis . I used all the harness out of the grand marquis everything works and runs good untill you stand on it hard .I have replaced all the sensors but the air charge and the map sensor . I replaced the distributer,pick up,modjule.the car starts to spit and sputter and backfire . the timing has been set right fuel pressure is good .anyone have any ideas ?