In alt.home.repair, on Wed, 07 Apr 2021 20:24:26 -0400, "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
I made a lot notes based on what he said.
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 would 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?
Just enough to fix my car, and maybe a little more. :-)
I used the scanner today and the short and long term trims tracked the
results of the guy who made the video, at idle and up to 2500rpm. Also
the MAF value (in metric) and the ECT, Spark, Load, and IAT seemed on
track. Mine starts at OL and goes quickly to CL for both banks.
I forgot to look at the 02BnSn, but I think they're stored in the
scanner. Yes, I posted them below, if that's what Review refers to.
The scanner is inside with me, but the notes are in the car. I'll post
them here later.
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.
He sprayed with water, hoping to hear a hiss, but not with carb clean.
I was going to spray with brake cleaner, because it says No Residue, but
maybe carb cleaner is better? (He didn't say why not, not a word about
spraying with other things.)
If that doesn't find it (and I did look everywhere I could think of last
year, using propane), I'm going to disconnect the purge solenoid and
plug that hose, and then disconnect the brake booster and plug that one,
the hoses that go into the throttle body. That's how he found a major
problem with his brake booster.
He used a vacuum tester to plug each hose in turn that goes to the
throttle body, but seems to me I don't need a tester. I can assume
there is some vacuum if the engine is running and it doesn't matter how
much, and all I need to do is use a pencil or something bigger to plug
each hose.
Last time when I was trying to find a vacuum leak, I didn't know and
didn't think about the fact that some leaks don't go to the outside,
like a leak in a hose does. He didn't name anything other than the
cannister circuit** and the brake booster that could have an internal
vacuum leak. There are so many hoses, I dont' have much confidence I
would think of something else even if it exists. Are there other things
I should disconnect? **The cannister circuit of couree includes a
long hose almost to the gas tank, which he couldn't feel or spray or
look at.
Fixing the brake booster lowered his trim total by 30 points but it was
still too high. He found that his MAF sensor was off somewhat and after
he replaced that too, everything was good. (Trim total was between +10
and -10.) I replaced my MAF sensor about 10,000 miles ago, on the hope
that would fix things. I only used a mimimal code reader th1en so if it
made any difference, I don't know, but it didn't get rid of the codes
and, I doubt if it's the problem now. AND today, I don't want to guess
what my MAF was at idle, but I know it was 9.5 at 2500RPM. His original
one started at idle (cold) 0.57 to idle (warm) 1.84, g/sec (and he said
2 to 3 would be better), but even at 2500 rpm, his value would never go
over 7 or 8, so I think mine works better. At least I think so.
I'm not sure what I see when I go to Review / Live Data / Location #1
(the only one listed). IIUC, the data there is from this afternooon and
it says
DTC_CNT is 2. That makes sense, P0171 and P0174.
02B1S2(v) is 0.680
B2 is 0.680 also
O2B1S1 is 3.279
02B2S1 is 3.250 very similar to bank 1
He had said that 3.3 is perfect 14.7 to 1, air to fuel ratio. My
two numbers are pretty close but maybe they'd be closer to 3.3 if ...
EQ_RATB2S1 is 0.988 but I don't know what that means and he didn't say,
and I havent' taken the time to look it up yet.
B1S1 is 1.006, very similar.
SHRTFTB1S2 is N/A.
while
SHRTFTB2S2 is 99.2 Isn't that strange? In the 4 values 8 lines up,
B1S2 and B2S2 are exactly the same. there something wrong with B1S2?
02SLOC is B1S12--B2S12-- whatever that means.
I hope I didn't give too much info.