93 gp 3.4l fouling plugs

this car would not start when i got it ,i changed the ignition mod. and spark plugs. it started and idled o.k. for a while,then deteriorated pretty rapidly untill it wouldnt start again. i took it to the dealership and they said the cat was melted down. ireplaced the cat and mufflers and put in a fresh set of plugs. it did the same thing, fouling the plugs after a short while. this is my third set of plugs and the car isnt even on the road yet. the car has 124,000 miles on it and the plugs are feul fouled [black,dry,smells like raw feul]any ideas?

Welcome to AF!!

I responded to your PM. Sounds like a bad O2 sensor putting too much fuel into the engine. Can happen with a cat goes bad as it destroys the O2 sensor at the same time.