Two
There are four total oxygen sensors. One before and one after the catalytic converter on each side of the engine.
Two. One before, and one after catalytic converter.
The oxygen sensors are screwed into the exhaust pipe near the catalytic converter.
Two sensors, and replace them.
Counterclockwise to remove, clockwise to tighten.
Gas engine has two, diesel has zero.
The O2 sensors are screwed into the exhaust system. Follow the exhaust backward from the engine and you will find the sensors.
According to the engine wiring schematic in my Chilton book : For a 1999 Ford Ranger , 4.0 liter EFI , V6 engine : ( there are 3 oxygen sensors )
Probably just in front of or just behind the converter(s)
On the 4.0 L OHV engine - 2 oxygen sensors - and one sensor used as a catalyst monitor for catalytic converter efficiency mounted downstream of the converter On the 4.0 SOHC engine - 2 oxygen sensors and 2 catalyst monitors
The oxygen sensors control the amount fuel in the engine and if it is making too many emissions the oxygen sensors will cut back on the fuel or if they are worn out they will increase the amount of fuel. The catalytic converter will eventually get plugged up if the Oxygen sensors are bad. The oxygen sensors control the converter.
2. one before the catalytic converter and one after.