Okay thanks..now there's a big problem in gas milage I used a half tank and only drove 150 miles?? I just changed plugs and wires. So I don't know wats wrong.. my cel light is on and its the po420 code but the muffler shop said its a new cat on it so idk what it could be and this is a 2002 3.8 as any help would be greatly appreciated. Thanks