You have one in each of the exhaust manifolds. it might be on the cross-over pipe behind the engin
motorcraft . com just shows ( 1 ) oxygen sensor for all available engines in a 1991 Ford Ranger
I'm not a mechanic / technician but on a 1988 Ford Ranger there might be ( 1 ) oxygen sensor ( upstream sensor )
On the firewall on the pass side.
The O2 sensor after the catalytic converter.
the o2 sensor is located on the exaust manifold
you can breath
It just has ( 1 ) oxygen sensor , before the catalytic converter ( upstream )
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 .
On a Ford Ranger ( V6 engine ) Bank 2 is the drivers side of the engine Sensor 1 would be close to the engine before the exhaust enters the catalytic converter
in the exhaust pipes behind & in front of converters
There is one in the exhaust system before the catalytic converter and sometimes one after it.
sending wrong fuel ratio mix