There are 4 sensors in total on the V-6. Two are mounted in each Pre-cat mounted within the exhaust manifold. These smaller cats help the cars computer get into closed loop status faster to further reduce emissions. The upper sensor in each pre-cat are the main O2 sensors. The lower ones monitor their activity. The main cat has no sensors and can easily be gutted if that's what you want. There is a recall on the pre-cats, if you have under 80,000 miles and you are getting a CEL light on the car with codes P0420(Bank #1) or PO430(Bank #2) Ford will replace the precats for free. Not sure if this is applicable to Canadian cars though. The exhaust manifolds are difficult to get to and replace, or to gut them properly. The bank closest to the fire wall is Bank #1, Bank #2 is the side facing the radiator.
