Everyone told me that my buddy's b4000 has 4 O2sensors. It is a SOHC, but I forgot the year(2000 or 2004 I think) 4x4. I could only find 2 in the Y pipe right behind the manifolds on either side, and one right behind the first cat I believe. Truck was missing and getting under 15mpg before and after new 02's, throwing o2 sensor codes.

 

u might only have 3 o2 a lot cars do