From: csr684@NOTyahoo.com   
      
   Scott Dorsey wrote:   
   > micky   wrote:   
   >> In rec.autos.tech, on 27 Mar 2021 19:31:15 -0000, kludge@panix.com   
   >> (Scott Dorsey) wrote:   
   >>   
   >>> AK   wrote:   
   >>>> I had an oxygen sensor replaced.   
   >>>>   
   >>>> Prior to that I got 20 mpg in the city for my CX7.   
   >>>>   
   >>>> Now I am getting 21.5 mpg.   
   >>>>   
   >>>> Could that increase be due to the replacement of the O2 sensor?   
   >>> If your O2 sensor was reading low and causing the computer to run the   
   >>> engine too rich, then yes.   
   >> So if now I get codes P0171 and P0174, which means that both banks are   
   >> running lean, does that mean replacing the sensors will cause the   
   >> opposite of what AK had, richer mixturen and decreased mpg?   
      
      
   Changing the sensors will do nothing but show the same codes again.   
   Those codes you posted mean the sensors are working. They are seeing   
   that there is excess oxygen in the exhaust stream compared to what they   
   expect based on the incoming airflow numbers.   
   The issue is not them but in the engine. As both are full bank lean   
   codes I would look at the fuel trims and the O2 live data and check for   
   vacuum leaks or an intake leak that is letting in unmetered air.   
   As you don't post any P0300 range codes I doubt it's fuel pressure as   
   that will commonly set misfire codes as well as the lean codes.   
      
      
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   Steve W.   
      
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