it depends on the engine for exact location, and number of O2 sensors, but on my 01 2.3l ranger there are 2, and they are easy to see. look for the exhaust manifold, and imagine you are traveling towards the back of the truck from the manifold. the first one is right past the manifold, and the second one is just a foot or two past that one. The one closest to the exhaust manifold can be seen from looking in the engine compartment. the second one you have to get under the truck to see. have fun getting them off....
I was looking in my Chilton book at the engine wiring schematic for a 1993 Ford Ranger 2.3 liter 4 cylinder and I only see ( 1 ) heated oxygen sensor
the o2 sensor is located on the exaust manifold
I'm not a mechanic / technician but the engine wiring schematic for the 3.0 liter V6 engine in a 1994 Ford Ranger that is in my Chilton's repair manual does not show a knock sensor
in the exhaust pipes behind & in front of converters
there are 2 and they are both under the vehichle on the exaust manifold
Exhaust manifold.
Looking at the 1991 Ford Ranger - 4.0 L V6 - engine wiring schematic in my Chilton repair manual , it shows ( ONE ) heated exhaust gas oxygen sensor
it is located right below the exaust manifold flanges above the catalitic converter
I'm not a mechanic / technician but the engine wiring schematic in my Chilton repair manual for the 2.3 in a 1994 Ford Ranger does not show a knock sensor
look right before the converter unless your pipes has been changed
there are 2, upstream which is under the exaust manifold flanges and the downstream which is in the exaust pipe
motorcraft . com just shows ( 1 ) oxygen sensor for all available engines in a 1991 Ford Ranger