My Chilton repair manual engine wiring schematic shows ( 3 ) - 2 would be for air / fuel ratio and the 3rd would be a catalyst monitor
There are three, two just below the manifolds and one after the catalytic.
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 )
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
If it's like a 1991 Ford Explorer ( with the 4.0 liter V6 engine ) It has ( 1 ) oxygen sensor
89 5.0 has 2, o2 sensors.
The oxygen sensor on a 1999 Oldsmobile Intrigue 3.3 liter is in the exhaust manifold/pipes
The 5.0 liter V8 has ( 4 ) oxygen sensors The 4.0 liter EFI ( which is an over head valve / pushrod design ) has ( 3 ) oxygen sensors Note: The 2 upstream oxygen sensors are used for adjusting the air / fuel ratio of the engine , the other oxygen sensor (s) are called catalyst monitors and monitor the performance of the catalytic converter(s)
There are four.
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
any car after 1995 has two, or four oxygen sensors,as they use OBDII system
That engine has 2 of them.
Two