all i saw after the cat was just piping, hangers, resonator and the mufflers.

 

They're placed inside of the cat; remember, they're there to measure correct A/F flow.

 

hiwords, when you say 2 pre and 2 post cat, i'm assuming you mean one on each side right?


also theoretically, if my cats are bad, would that cause the 2 sensors in the cats to be defective (and hopefully avoid replacing 4 o2 sensors)