[Markstang690]

So I was doing a little work on my exhaust getting rid of an annoying rattle.. and I happened to look over my cats.. and noticed and wondered.. why are both my O2 sensors actually in front of my main cat? like it goes header, O2, pre-cat, O2, main cat.. anyone know whats up with that?

[97stang3.8]

the front o2 tells the computer if the engine is running rich, lean, or not completing its burn. the rear o2 tells the computer how well the cats are working.

[Markstang690]

ok i get that.. but why is the main cat behind the last o2 sensor.. where it is it seems that the O2 sensor doesnt care much about the main cat.. like it cant monitor what the main cat is even doing

[97stang3.8]

it probably assumes that if all is right in the first cat then nothing will be wrong with the second.