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post #1 of 33 Old 05-25-2017, 10:21 AM Thread Starter
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Air Fuel Ratio Accuracy

How accurate are the air fuel ratios shown in the ecu compared to an aftermarket afr gauge?

I was recently battling electronic gremlins. My car kept blowing the EFI No.2 fuse. The problem corrected itself after a week. But in the course of looking for a short, I ran the car temporarily with no oxygen sensors or the maf sensor plugged in. Lo and behold, the Torque app was still displaying a "Measured" air fuel ratio. How was it measured???

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post #2 of 33 Old 06-02-2017, 05:36 PM
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I would assume if it doesn't receive a signal, the ecu will run in a limited mode, and will "presume" what the AFR is. Since there isn't mention of what car, there could be 2, 3 or 4 O2 sensors as well.

When you say "aftermarket AFR gauge" you should be more specific - if you're just using something that is reading the OBD2 port, then you really aren't using an aftermarket gauge, just using something that displays what the stock system shows.

An aftermarket AFR gauge (at least anything worthwhile) is usually coupled with something like an Innovative wideband sensor/controller.

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post #3 of 33 Old 06-03-2017, 04:07 PM Thread Starter
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I have a 2009 Avalon. 4 o2 sensors.

By "aftermarket" I meant a pod gauge with its own dedicated o2 sensor. Something like this... https://www.amazon.com/AEM-30-4110-U...+o2+sensor+kit

Right now, I am using a bluetooth OBD2 adapter and a tablet with the Torque Pro app installed. To My understanding, the Torque app just shows the information as the car's ecu is interpreting it. At wide open throttle, according to the torque app, the afr bottoms out at 12.08 and sits there. Since, I've had the app, I've switched from a short ram to a cold air intake, went from single to dual exhaust, and installed headers. Still, I get the same 12.08 afr at wide open throttle. I was just wondering how accurate these numbers actually are.

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post #4 of 33 Old 06-06-2017, 12:11 AM
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I had people over the years tell me the OBD2 port ECU air/fuel ratio readings are inaccurate because it's range of reading is limited. A wide band a/f ratio gives a wider range. However, my Torque pro App usually reads right on par with a dyno air/fuel ratio reading that would be connected to my rear tail pipe. So I stuck with my OBD2 port readings and use it as a cheap tool.



Quote:
Originally Posted by Moondoggy-X View Post
How accurate are the air fuel ratios shown in the ecu compared to an aftermarket afr gauge?

I was recently battling electronic gremlins. My car kept blowing the EFI No.2 fuse. The problem corrected itself after a week. But in the course of looking for a short, I ran the car temporarily with no oxygen sensors or the maf sensor plugged in. Lo and behold, the Torque app was still displaying a "Measured" air fuel ratio. How was it measured???

With your oxygen sensor unplugged, your car can run based on the maf sensor reading and make an assumption on how much fuel it needs to add. With the maf sensor unplugged, perhaps it can do the reverse based on the amount of oxygen detected by the O2 sensor. I thought it would not have a reading though if the oxygen sensor is unplugged. The maf sensor unplugged should not show a maf sensor g/s reading. Interesting to know where the Torque app is getting a reading from when they are unplugged.

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post #5 of 33 Old 06-06-2017, 12:22 AM
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Air Fuel Ratio Accuracy

Quote:
Originally Posted by Moondoggy-X View Post
I have a 2009 Avalon. 4 o2 sensors.



By "aftermarket" I meant a pod gauge with its own dedicated o2 sensor. Something like this... https://www.amazon.com/AEM-30-4110-U...+o2+sensor+kit



Right now, I am using a bluetooth OBD2 adapter and a tablet with the Torque Pro app installed. To My understanding, the Torque app just shows the information as the car's ecu is interpreting it. At wide open throttle, according to the torque app, the afr bottoms out at 12.08 and sits there. Since, I've had the app, I've switched from a short ram to a cold air intake, went from single to dual exhaust, and installed headers. Still, I get the same 12.08 afr at wide open throttle. I was just wondering how accurate these numbers actually are.


From my understanding, what Torque is showing in the A/F analyzer is what the ECU is trying to actually get accomplish, not what the actual AFRs actually are.

I too was looking at the AEM UEGO or the LC2 Innovate kit after not getting what I needed from TorquePro.

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post #6 of 33 Old 06-06-2017, 12:24 AM
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Torque can only work with the data stream handed off by the PCM, likely as mentioned it goes to assumed values. 12.8 is way too rich for idle on a warmed engine, but normal for a cold engine. Stock narrow band sensors are only accurate through a narrow range, however newer cars are using wide band style A/F sensors which are as good as the stand alone sensors.
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post #7 of 33 Old 06-09-2017, 06:24 PM
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Yep, the 2009 Avalon uses a wideband unit for the upstream sensor. So yes, it's as accurate as AEM aftermarket wideband unit.

Quote:
Originally Posted by Moondoggy-X View Post
Right now, I am using a bluetooth OBD2 adapter and a tablet with the Torque Pro app installed. To My understanding, the Torque app just shows the information as the car's ecu is interpreting it. At wide open throttle, according to the torque app, the afr bottoms out at 12.08 and sits there. Since, I've had the app, I've switched from a short ram to a cold air intake, went from single to dual exhaust, and installed headers. Still, I get the same 12.08 afr at wide open throttle. I was just wondering how accurate these numbers actually are.
With the introduction of wideband O2-sensor usage in OEM applications, ECU algorithms have changed to full-time closed-loop (using feedback). This actually makes it easier to hot-rod your car since ECU will detect the changes and adjust fuel & ignition. However, that assumes that stock programming is fully-optimised for power, most of time it's compromise of multiple variables such as emissions, durability & longevity with power-production being further down list of priorities.

ECU uses various input sensors such as MAF, TPS, RPM, engine-coolant temp and air-temp sensors to arrive at initial injector pulse-width (duty-cycle). Then it uses the O2-sensor as feedback sensor to make minor adjustments to keep AFR on target with desired values at that operating range. So... if pre-programmed target is 12.08:1 AFR under WOT @ 6000rpms, then ECU will adjust injector duty-cycle (STFT) to arrive at that same 12.08:1 ratio regardless of mods.

So... let's say all your mods resulted in an increase of +5% air-flow at 6000rpms, the extra air-flow would cause a leaner AFR the 1st time you run through WOT map. ECU will detect a leaner-than-desired mixture and re-adjust its STFT to +5% to re-hit its desired target of 12.08:1. Even though the AFR is same, you may actually have more air and more fuel than stock (and more power). So the figures you want to examine are STFT and LTFT values at those operating ranges to see if you indeed are making more power.

Similarly, those mods will result in less flow at lower-RPMs, up to say... 3000rpms. So again, look at your STFT and LTFT for WOT @ lower-RPMs and you may see a -5-10% reduction in fuel to match lower air-flow.

At WOT, 12.08:1 is a safe AFR and little rich for max-power, but still much better than the older Toyotas which was programmed around 10.5-11.0:1. Max-power on an NA engine typically occurs around 13.0-13.5:1, but you have to be spot-on most of time. Less leeway for intake-leaks or sub-standard gasoline than richer mixtures.
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post #8 of 33 Old 06-09-2017, 10:14 PM
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Quote:
Originally Posted by DannoXYZ View Post
Yep, the 2009 Avalon uses a wideband unit for the upstream sensor. So yes, it's as accurate as AEM aftermarket wideband unit.

With the introduction of wideband O2-sensor usage in OEM applications, ECU algorithms have changed to full-time closed-loop (using feedback). This actually makes it easier to hot-rod your car since ECU will detect the changes and adjust fuel & ignition. However, that assumes that stock programming is fully-optimised for power, most of time it's compromise of multiple variables such as emissions, durability & longevity with power-production being further down list of priorities.

ECU uses various input sensors such as MAF, TPS, RPM, engine-coolant temp and air-temp sensors to arrive at initial injector pulse-width (duty-cycle). Then it uses the O2-sensor as feedback sensor to make minor adjustments to keep AFR on target with desired values at that operating range. So... if pre-programmed target is 12.08:1 AFR under WOT @ 6000rpms, then ECU will adjust injector duty-cycle (STFT) to arrive at that same 12.08:1 ratio regardless of mods.

So... let's say all your mods resulted in an increase of +5% air-flow at 6000rpms, the extra air-flow would cause a leaner AFR the 1st time you run through WOT map. ECU will detect a leaner-than-desired mixture and re-adjust its STFT to +5% to re-hit its desired target of 12.08:1. Even though the AFR is same, you may actually have more air and more fuel than stock (and more power). So the figures you want to examine are STFT and LTFT values at those operating ranges to see if you indeed are making more power.

Similarly, those mods will result in less flow at lower-RPMs, up to say... 3000rpms. So again, look at your STFT and LTFT for WOT @ lower-RPMs and you may see a -5-10% reduction in fuel to match lower air-flow.

At WOT, 12.08:1 is a safe AFR and little rich for max-power, but still much better than the older Toyotas which was programmed around 10.5-11.0:1. Max-power on an NA engine typically occurs around 13.0-13.5:1, but you have to be spot-on most of time. Less leeway for intake-leaks or sub-standard gasoline than richer mixtures.
Excellent post and thank you.
We can clear this ALL up very easy. I've been hitting that 12.08:1 during my recent WOT runs on my RAV4. So....Moondoggy, can you post up your STFT and LTFT? I mean, I know you can as well as I since we both have that data. Seems it'd be an excellent tool to utilize.

So....if you are seeing +STFT and/or +LTFT, that may be an indication that you are making more power since the ECU is adding more fuel? Is this what is being said?

Edit: Just went downstairs to see if I could do check and post STFT and LTFT. Yep....unfortunately, I swapped ECUs this Thursday. Grrr..... So Yeah Moondoggy! If you could post that info up, would be cool stuff.

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post #9 of 33 Old 06-09-2017, 10:54 PM
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You need to graph those values vs. RPM to get useful data.
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post #10 of 33 Old 06-12-2017, 07:46 PM Thread Starter
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Well, with about 90 degree intake temps(Northern Illinois is in the middle of a heat wave), both the LTFT and STFT were bouncing between +3 and -6. With normal throttle, the values were alternating between banks. One would go + and the other would go -, then they'd switch. Afr was bouncing between 14.5 and 15.0. At wide open throttle, the ltft would freeze at whatever number it was at before wot, and the stft would drop to 0.00. AFR then bottomed out at 12.08. The ltft, stft, and afr holds those values throughout the rev range while at WOT. Even while changing gears.

I would have take a video but its not really possible with the way my tablet is mounted in the car.
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post #11 of 33 Old 06-12-2017, 08:01 PM
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interesting data, yea it was a little warm today.
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post #12 of 33 Old 06-12-2017, 08:15 PM Thread Starter
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What's also interesting is that Myxalplyx's Rav4 runs so much leaner from the factory. We both have 2gr-fe's. His is a 2010, mine is a 2009. His AFRs were 13.0-13.5 at wot before his tune. They added 20% to his STFT to have the same 12.08 AFR I have from the factory.

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post #13 of 33 Old 06-12-2017, 08:20 PM
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Interesting, would be neat to compare the factory fueling and timing and vvt tables between years of the same engine. And also compare against Lexus models too.
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post #14 of 33 Old 06-13-2017, 11:36 AM
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Are we able to extract the native fuel & ignition tables via OBD-II? That would be interesting to examine.


Quote:
Originally Posted by Moondoggy-X View Post
What's also interesting is that Myxalplyx's Rav4 runs so much leaner from the factory. We both have 2gr-fe's. His is a 2010, mine is a 2009. His AFRs were 13.0-13.5 at wot before his tune. They added 20% to his STFT to have the same 12.08 AFR I have from the factory.
And with wideband O2, there should also be a target AFR table somewhere as well.
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post #15 of 33 Old 06-13-2017, 01:46 PM Thread Starter
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Quote:
Originally Posted by DannoXYZ View Post
And with wideband O2, there should also be a target AFR table somewhere as well.
The Torque app can display the commanded, or target air/fuel ratio and the measured or actual air/fuel ratio.

While cruising, my car gas a target afr of 14.69 and actual afr bounces between 14.3 and 15.1.

While decellerating, the target afr is 13.59 and the actual tops out at 18.12. No bouncing.

While at wide open throttle, the target afr actually changed with the rpm. It started at about 11.9 and dropped to 11.1 at the top of the rpm range. The actual afr bottomed out at 12.08 and dis not move.

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