This is only going to answer half of the question :
On a 1995 Ford Explorer , 4.0L EFI , V6 engine ( which is an Over Head Valve /
pushrod design )
There are ( 2 ) oxygen sensors
* I BELIEVE they are in the outlets of each exhaust manifold *
That would depend on what year of Ford Explorer and which engine you have ( my 1995 Ford Explorer with the 4.0 liter OHV , V6 engine has ( 2 oxygen sensors )
A 1994 Explorer has 2 oxygen sensors, they are either screwed into the exhaust manifolds at their outlets or into the ehaust pipes near the engine.
There are 2 oxygen sensors.
My Chilton repair manual - engine wiring schematic shows ( 2 ) heated oxygen sensors for the 1993 Ford Explorer
On a 1998 Ford Explorer XLT : With the 4.0 liter SOHC V6 engine ( 4 oxygen sensors , the 2 closest to the engine are used for adjusting the fuel ratio and the other 2 are catalyst monitors There are also ( 4 oxygen sensors if you have the 5.0 liter V8 engine )
4 ======================================================= The above answer is correct if you have the 5.0 liter V8 engine in your 1996 Ford Explorer , but if you have the 4.0 liter EFI , V6 engine ( VIN " X " ) there are ( 3 oxygen sensors )
On a 1998 Ford Explorer Sport : If it has the 4.0 litre EFI engine ( which is an over head valve / pushrod design engine / the 8th character of the VIN is an " X " ) there are ( 3 oxygen sensors ) If it has the 4.0 litre SOHC engine ( the 8th character of the VIN is an " E " ) there are ( 4 oxygen sensors )
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
A 2001 Ford Explorer Sport , with the 4.0 liter Single Over Head Cam V6 engine should have ( 4 oxygen sensors )
According to my Haynes repair manual : For a 1997 Ford Explorer , 4.0 liter Single Over Head Cam , V6 engine : The engine wiring schematic shows ( 4 ) oxygen sensors
( 2 ) oxygen sensors ( I BELIEVE they are in the outlet areas of the exhaust manifolds )
two