In rec.autos.tech, on Sat, 03 Apr 2021 02:07:24 -0400, "Steve W."
wrote:
Scott Dorsey wrote:
micky wrote:
In rec.autos.tech, on 27 Mar 2021 19:31:15 -0000,
(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
I did buy a code reader last year that would read the live data, but
what I should look for has been mostly a mystery since then, until the
video below. I found it a few days ago but just had time to watch it.
Cars are much more complicated than when I was a boy, or even a
teenager, and I've said for years and told quite a few people that
anyone smart enough to be a good mechanic these days could succeed in a
lot of fields.
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.
Thanks. I found a long video that went over at least some of the
things to do with a P0171.
https://www.youtube.com/watch?v=SugtR4KMIDU
He ended up finding a leaky brake booster and a somewhat bad MAF sensor,
but more importantly he goes into some detail about what everything
means.
You and some of the other people here know everything that is in this
video. I miss the days when there were people here who knew less than I
do. They woudl benefit more from this post than you or the others here
will.