1991 Chevy Camaro 5.7 engine missing and fouling plugs.

5.7 engine in Z28 Camaro. Changed plugs twice, changed plug wires, cap, rotor button. Changed distributer, pick up looked rusted, changed map, IAC. Checked for vaccuum leaks, unable to find with carb cleaner. Checked vaccuum hose on fuel pressure regulator, didn't see any fuel. Had cats checked by two different muffler shops, both said they were open. It really has a bad smell from exhaust. Also in timing this car I unplugged the white wire from wiring harness, is that the right one, only one I see seperated from harness. Timing is moving around a good bit. No check engine light, checked codes anyway, no codes. Have you ever seen this on these vehicles?