MAF sensor and O2 sensor bad?

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Michael Gain

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I had a little time this morning before work and thought I would troubleshoot an annoying idle issue (bogs slightly when coming to a stop, and occasionally will vibrate the steering wheel when parked).

Using my handy iid tool to log live values, this what I see:

Screenshot_20210223-074450.png


I can lack common sense sometimes, but I see the driver side maf is under reporting and the engine is adding even more fuel (stft) to its learned value (LTFT). Does everyone concur that driver side maf needs replaced (it's already been cleaned a couple of times since ownership.

Also, I am confused by the o2 sensor readings. These are the o2 sensors after the exhaust manifold o2 sensors, but before the cats. One is super positive and one is super negative. What is this telling me?

Thank you as always for your wisdom and guidance!
 

DaytonaRS7

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there is something very wrong.

do you have any CEL? id be surprised that the MAF reading and o2 readings arent throwing codes.
Assuming your bank 2 MAF sensor is faulty (reading too much airflow), it is affecting your bank 2 o2 sensor readings (too high oxygen) which is then going to most likely cause your STFT to be very negative (missing data).

can we get more data...for comparison? fill in the question marks below.
Bank 1 LTFT +7.81%
Bank 1 STFT +8.59%
calculated total fuel trim +16.4%. this is too high. unrelated to the above underlined part.

Bank 2 LTFT +9.38%
Bank 2 STFT ??

Bank 1 sensor 1 ??
Bank 1 sensor 2 ??
Bank 2 sensor 1 +99.2%
Bank 2 sensor 2 -100%

start by replacing your MAF sensor(s) and run a bottle of bg44k though the fuel system.
 
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Michael Conley

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I just replaced my bank 1 upstream O2 sensor as it was preventing my emissions monitors from getting ready. No CEL, no DTC so it can be a bit of rabbit hole. Have you tried cleaning your MAFs first?
 

jlglr4

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The one MAF looks faulty, but this alone should affect your fuel trims and o2 sensors on both banks to roughly the same degree because the MAF-measured airflow is combined before entering the engine. Maybe we’ll see that with the STFT posted.

I’m guessing the STFT sensor 2 is the O2 sensor, but I’m not sure what the percentage correlates to. Isn’t there a reading that will give o2 sensor voltage?
 

Michael Gain

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there is something very wrong.

do you have any CEL? id be surprised that the MAF reading and o2 readings arent throwing codes.
Assuming your bank 2 MAF sensor is faulty (reading too much airflow), it is affecting your bank 2 o2 sensor readings (too high oxygen) which is then going to most likely cause your STFT to be very negative (missing data).

can we get more data...for comparison? fill in the question marks below.

start by replacing your MAF sensor(s) and run a bottle of bg44k though the fuel system.

I was thinking bank 1 is faulty due to measuring too little air flow--element contaminated.

No codes other than those related to the start stop stuff.

Here is some better data:

Idle after leaving work:

Screenshot_20210223-174943.png


Just pressed accelerator after slowing down:

Screenshot_20210223-175527.png


Coasting, foot off of accelerator:

Screenshot_20210223-175918.png


Obviously these are screen shots, but the live data shows significant drop in bank 1's maf reading once the accelerator pedal is released.

Also, LTFT and STFTs reduce (less positive) when accelerating or when the throttle is open, and increase (more positive) when coasting.

Symptoms of a vacuum leak in addition to the faulty MAF?
 

Michael Gain

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I just replaced my bank 1 upstream O2 sensor as it was preventing my emissions monitors from getting ready. No CEL, no DTC so it can be a bit of rabbit hole. Have you tried cleaning your MAFs first?


Yes they have been cleaned a couple of times since I owned it. Any and all feedback is appreciated!
 

Michael Gain

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The one MAF looks faulty, but this alone should affect your fuel trims and o2 sensors on both banks to roughly the same degree because the MAF-measured airflow is combined before entering the engine. Maybe we’ll see that with the STFT posted.

I’m guessing the STFT sensor 2 is the O2 sensor, but I’m not sure what the percentage correlates to. Isn’t there a reading that will give o2 sensor voltage?

There is a voltage value. I will try that next!

As far as consolidated air flow, you are right, and I thought the same thing, but the maf readings affect their assigned bank; or so I've been told...
 

jlglr4

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That’s strange. Airflow should be solely dependent on engine RPM, and your engine RPM in each of those screens above is almost exactly the same. Just in that last screen the one MAF goes way off. Must be a bad MAF, right? I can’t think of another possibility for that.

I also don’t see how the individual MAFs can affect the right or left banks independently. Just doesn’t seem possible.

The SFTF sensor 2 readings look the same now. In that first post, the bank 2 sensor was at -100% (which I assume is no reading). I wonder if the GAP tool just didn’t pull it up properly. I have gotten glitches like that sometimes.

Let me know if you want me to run any numbers on my GAP tool for comparison.
 

Michael Gain

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That’s strange. Airflow should be solely dependent on engine RPM, and your engine RPM in each of those screens above is almost exactly the same. Just in that last screen the one MAF goes way off. Must be a bad MAF, right? I can’t think of another possibility for that.

I also don’t see how the individual MAFs can affect the right or left banks independently. Just doesn’t seem possible.

The SFTF sensor 2 readings look the same now. In that first post, the bank 2 sensor was at -100% (which I assume is no reading). I wonder if the GAP tool just didn’t pull it up properly. I have gotten glitches like that sometimes.

Let me know if you want me to run any numbers on my GAP tool for comparison.

With consolidated airflow, I am with you. No way that each bank's measured air molecules makes it into that bank's cylinders, through one throttle body, and churned up by the supercharger. But, I wouldn't be surprised if a land rover engineer thought it was a good idea...

Ignore the rpm at the top. It never changed... at a stop light, I actually logged rpm as well. Must have been a glitch.

Thank you for the comparison offer. I think the low reading MAF is at fault, but I will replace them both. I also have all the parts necessary to replace the exhaust manifold gaskets. I am not sure of a leak there would cause a rich or lean reading at the o2 sensor though.

I already smoke tested the engine once, but will do it again to rule out a vacuum leak.
 

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