i own a 1981 caddy deville with the 6.0L v8. it has the 4-6-8 thing on it. i know what that is, but the problem i'm haveing is she runs really rich, why is that? and the 4-6-8 option doesn't work, it is continuasly using 8 cylinders, how do i fix that?

Optional Information:
1981 Cadillac sedan deville 6.0L v8

Already Tried:
checked compression, and replaced spark plugs. i plan to replace the water temp. sensor, and plug wires.