micky wrote:
> In rec.autos.tech, on Thu, 08 Apr 2021 02:05:14 -0400, "Steve W."
> > wrote:
>
>> Steve W. wrote:
>>> Steve W. wrote:
>>>> micky wrote:
>>>>> 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.
>>>> I don't know everything but I'm pretty good at diagnostic and repair
>>>> work on vehicles.
>>>>
>>>> How much do you really want to know about modern engine diagnostics?
>>>>
>>> Oh where he is checking the hoses, a quick trick is to use carb cleaner
>>> and spray it around the hoses. If the engine rpm suddenly jumps look in
>>> the area you were spraying for a leak.
>>>
>> From what you posted you have a vacuum leak/pirate air issue as the
>> primary problem. You can use brake clean or carb cleaner, they are both
>> more or less paint thinners that burn ok. I use carb cleaner because the
>> older version of brake cleaner is chlorinated and generates toxic gas
>> when burned.
>
> Oops, I don't want that. I ordered it online and haven't gotten it yet,
> but it also says the original version is not flammable (unlike the other
> three versions in green cans, without chlorine),
>
> So how could it work at all if it's not flammable?
>
> There's a chart about a fifth of the way down, comparing 5 different
> version of Brakleen. Only in the red can is there chlorine but only that
> one is Not Flammable!
> https://www.amazon.com/CRC-05089-BRA..._t1_B000BXKZUQ
>
> But in videos I watched, they're using Brakleen in that red can! Life
> is so complicated.
>
>> The thing to remember though is that in the video he is working on a car
>> different than yours, some things apply, others don't. For instance MAF
>> flow, as engine sizes go up, MAF numbers increase even at idle to feed
>> the larger engine.
>
> Yes, I see. The engine he's working on is only 4 cylinders. Mine is 6.
>> Try this
>> https://support.alldata.com/sites/ma...ing_110918.pdf
>
> I'll print this and do as he says tomorrow.
>> Looking at the fuel trims that go up, then start coming down means that
>> it's a medium sized leak. As the throttle opens it goes past the point
>> where the pirate air is the main component and the mixture improves. If
>> it started improving immediately it would be a small leak.
>
> Yes, I see.
>
>> For the sensor data you want to look at it live, and watch what it
>> actually reads, if the front sensors are changing voltages rapidly as
>> the engine runs and the rear sensors stay at a somewhat constant number
>> and don't vary like the fronts, the sensors are working and although
>> they may be worn, they are doing their job and the converters are working.
>> You may be surprised at where a vacuum leak can be, brake booster, PCV
>> system, intake manifold gaskets, a damaged port on the manifold, in the
>> EVAP system and a host of others, some external others internal.
>
> I'll keep looking and look again at places I've looked.
>
>> OH the wuse of water for leaks is somewhat common, it's because you can
>> use it on a hot or cold engine or one where you have ignition sources
>> like open plug wires or bad coils. The amount of cleaner you will use
>> won't be an issue though, just be sure to start on a cold engine.
>> Usually something like an intake leak will get better as the engine
>> warms up so you want to catch it when it's cold.
>
> Okay.

If you like visit 2carpros.com Put in as much info about your issue as
you can and one of the crew can look up the line routing and parts on
that car and give you much more info including pictures and other tests.

--
Steve W.