If you are looking for the oxygen sensor, I don't know the exact location, but all oxygen sensors are located on the exhaust. Start looking from the manifold and follow the exhaust. They just screw into the exhaust pipes. Some are located on or close to the cadylac converter.
motorcraft . com just shows ( 1 ) oxygen sensor for all available engines in a 1991 Ford Ranger
There are 2 heated exhaust gas oxygen sensors , 1 screwed into the outlet on each exhaust manifold on a 1993 Ford Ranger 4.0 L .
I'm not a mechanic / technician but on a 1988 Ford Ranger there might be ( 1 ) oxygen sensor ( upstream sensor )
My 1995 Ford Explorer with 4.0 L OHV has 2 oxygen sensors (Helpfull)
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
you can breath
Check
A little more information please ( what year of Ford Ranger , what size is the engine ) As far as I know there could be as many as four oxygen sensors or as little as one depending on the year and engine size
That Vehicle has 2 oxygen sensors.
in the exhaust pipes behind & in front of converters
sending wrong fuel ratio mix
There is one in the exhaust system before the catalytic converter and sometimes one after it.