Sorry for the bombardment of questions

I purchased a Ford OBD 1 reader, and when I had it run the test I got codes 172 (O2 sensor not switching single or lean rear H2OS fuel control), 536 (something to do with the post catalytic fuel burn?) and 538 (Throttle position sensor or Idle Air control not working).

I did notice last night I do have an exhaust leak right behind the catalytic converter (still passed the dyno test with emissions), not sure if this is related?

 

What year Ranger, and what engine?

Ford 3-digit code list here: https://www.therangerstation.com/tec...gitcodes.shtml

536 is a test code, brake pedal, ignore it
538 is a test code, gas pedal, ignore it

for 172 need to know if you have a 4cyl engine or V6, and the year?

 

Its a 4.0L OHV in a 1993 4x2

Thanks again for all your help Ron

 

1994 and earlier Rangers don't have a Downstream(rear) O2 sensor and 4.0l is a V6, so the 172 code means the Upstream Right(passenger side) O2 sensor is showing high oxygen levels in exhaust on that bank of the engine

Since there is no code 176 shown(left side O2 was Lean) that would point to either a lower intake gasket leak on passenger side, a failing injector passenger side, or a failing O2 sensor passenger side

How old are the O2 sensors?
They last 150k miles or 10 years which ever comes first, they use a chemical reaction to detect Oxygen in the exhaust and they simply run out of chemicals over use and time
And they fail Lean
So if your O2 sensors are older then I would replace BOTH first, before investigating gasket leak or injector issues

An exhaust manifold leak on passenger side will also cause that code but you should hear a leak like that, sounds almost like a "ticking" rocker/lifter noise
Also a steady misfire on passenger side would cause that code, without good ignition in a cylinder the oxygen is not used up so goes into the exhaust and O2 sees that as Lean, so a failing spark plug or spark plug wire can cause a misfire, but you would FEEL that when under a load(driving)

A small drop in MPG would also be noticed as O2 sensors get older because the computer has to run engine Richer than needed to get the failing O2 sensor into correct voltage range
So new O2 sensors will pay for themselves over the next 150k miles in fuel savings