I am looking to determine the number of O2 sensors on a 2005 E-250 5.4L V8. I am finding conflicting information online. I am only able to locate three sensors: the two upstream sensors closest to the engine near the manifold, and one downstream sensor after the cat converter. Am I missing one?

 

 

The 2 on the exhaust manifold are to tell fuel and air results while the one after the converter tell if it cleaned the exhaust to EPA requirements..