Why do we trust widebands so much?

First thing, it seems like we should have a section in this forum for "tuning theory and discussion" or something like that?

More generally why do we put so much trust in deriving our airflow model for our modified engine from feedback from a O2 sensor that is reading a product of a bunch of other stuff that happened before it? Yes, I know the factory does it and they do it with narrowbands, I just don't see how this can be accurate given that the air has to find its way into the cylinder properly with proper motion, the fuel has to be injected at the perfect time, heat has to be distributed through the chamber correctly, spark has to be good, etc. All this has to happen for "good" combustion for us to get a proper air fuel ratio feedback from the wideband, or no? What am I missing here?

I don't understand how say having the spark advance retarded by say 5 or 10 degrees from optimal, which is very likely, how does this not interfere with combustion so much to a point where it artificially reads rich since there wasn't enough time for combustion? Or does combustion always happen by the time the charge hits the O2 sensor? and with that being said how does it not give a artificially lean reading given that all the fuel may have been used up but it didn't occur in the cylinder?

I used to know a little how narrowbands and widebands worked, but what I don't see is, if they "measure" the amount of excess oxygen, then how do they measure rich conditions if there is no excess oxygen to measure in a rich condition?

The wideband sensors use an internal chamber that is heated to about 1200F, with a platinum catalyst to finish reacting any unburnt fuel/air mixture. What is left in the chamber is either extra oxygen or extra fuel.

Then, it uses a bi-directional electro-chemical oxygen pump to either pump external oxygen in or out of the chamber to maintain a 450mv reading on its internal NB sensor.
The current, positive or negative, applied to the pump circuit determines how much oxygen was pumped in out out of the test chamber to maintain the lambda 1.0 ( 450mv ).
If it had to pump oxygen IN to the chamber, the mixture was rich. It if had to pump oxygen OUT of the chamber, the mixture was lean. The pump current is converted to o2% / lambda / afr.

That's why they can measure lean or rich mixtures. And, why wideband sensors need controllers, rather than just reading a voltage off of them, like a NB.

Also, in reality, a NB sensor can only really sense rich conditions. It measures the oxygen content of the exhaust gas vs. the atmosphere. If the difference is greater than some preset limit ( usually near the partial pressure of oxygen in the atmosphere STP ), it generates a voltage, based on the difference on either side of the sensor ( exhaust or free-air ). The curve is very steep. And generates about 1.0v at the maximum difference. Pending the sensor temperature, atmospheric pressure, and exhaust gas pressure. That's why they try to keep it at around 450mv. In the middle of its useful range.


As far as trusting them; that is a different story. It depends on the health of the sensor, the controller, and how it is connected to the logging device.

And that is a thread, all on its own :)

Quote:

---

Originally Posted by dr.mike

The wideband sensors use an internal chamber that is heated to about 1200F, with a platinum catalyst to finish reacting any unburnt fuel/air mixture. What is left in the chamber is either extra oxygen or extra fuel.

Then, it uses a bi-directional electro-chemical oxygen pump to either pump external oxygen in or out of the chamber to maintain a 450mv reading on its internal NB sensor.
The current, positive or negative, applied to the pump circuit determines how much oxygen was pumped in out out of the test chamber to maintain the lambda 1.0 ( 450mv ).
If it had to pump oxygen IN to the chamber, the mixture was rich. It if had to pump oxygen OUT of the chamber, the mixture was lean. The pump current is converted to o2% / lambda / afr.

That's why they can measure lean or rich mixtures. And, why wideband sensors need controllers, rather than just reading a voltage off of them, like a NB.

Also, in reality, a NB sensor can only really sense rich conditions. It measures the oxygen content of the exhaust gas vs. the atmosphere. If the difference is greater than some preset limit ( usually near the partial pressure of oxygen in the atmosphere STP ), it generates a voltage, based on the difference on either side of the sensor ( exhaust or free-air ). The curve is very steep. And generates about 1.0v at the maximum difference. Pending the sensor temperature, atmospheric pressure, and exhaust gas pressure. That's why they try to keep it at around 450mv. In the middle of its useful range.


As far as trusting them; that is a different story. It depends on the health of the sensor, the controller, and how it is connected to the logging device.

And that is a thread, all on its own :)

---

Thanks for the info. I guess the fact is we don't have any other instrument to use that compares to a wideband in terms of ease of installation and cost, or do we? It just really feels like to me we put way to much trust in it, so we believe our MAF and VE is calibrated perfectly. For example, I have a Rotofab which is supposed to remain unchanged from the stock MAF tube to where it shouldn't need a recalibration, but people even with stock MAF locations/tubes still recalibrate the MAF, are they actually making it worse and introducing more error? I believe no one is as good as GM is at calibrating the MAF right?

Quote:

---

Originally Posted by cmitchell17

but people even with stock MAF locations/tubes still recalibrate the MAF, are they actually making it worse and introducing more error?

---

Yes, this bugs the shit out of me lol. I'm sure there was a writeup years ago somewhere that became gospel and nobody mentioned that if you don't move or alter the MAF, you don't have to recalibrate it. In fact, with a stock MAF and intake tube, you can calibrate VVE without ever so much as looking at a fuel trim. You already have a reliable airflow baseline and there's even less steps in between, so it's basically a no-brainer.

GM's stock calibration is based on a standard set for a particular MAF sensor given to them by the manufacturer. They are electronic sensors and I am sure that they are not all exactly the same. There are tolerances in everything that is manufactured. GM does not individually tune every vehicle, that leaves the manufacturing facility. Not saying the tune is wrong or very far off, but the tuning process we go through with HP Tuners tunes the MAF or VE table to that exact vehicle and the environment that it is performing in. Granted your still relying on a mass produced wideband sensor to give you the necessary information needed to calibrate the MAF. So take it with a grain of salt, I tune the maf even if it's on a factory air intake just because that's the way I learned to tune.

When the sensors are new, they are remarkably consistent. The BOSCH sensors are laser trimmed, at the factory, under standard calibration conditions. So that, if the controller is designed properly, the output will be within 1% between sensors. The NTK sensors are tested at the factory , and get a resistor installed that indicated its calibration. But, almost nobody in the aftermarket knows how to match the resistors to the sensor calibration. So, they tend to need free-air calibration.

So, if you can verify the calibration of your sensor. And, you have a known good controller and logger interface, you can trust your WB readings. Probably more so than a MAF.

Thanks everyone for the help. Smokeshow, do you think the stock GM Maf calibration is more accurate than if you were to recalibrate it with a wideband? or is the difference probably negligible?

I have a Rotofab, which claims it works with the stock MAF calibration, I am just wondering if I am making it worse trying to recalibrate the stock calibration?

Quote:

---

Originally Posted by cmitchell17

Thanks everyone for the help. Smokeshow, do you think the stock GM Maf calibration is more accurate than if you were to recalibrate it with a wideband? or is the difference probably negligible?

I have a Rotofab, which claims it works with the stock MAF calibration, I am just wondering if I am making it worse trying to recalibrate the stock calibration?

---

When you bring another onboard sensor into the mix, you're assuming that sensor is a better source of information than what you're calibrating. In the case of widebands, you just have to take the data you get with a grain of salt... It may tell you the MAF is perfectly calibrated or it may tell you it is 15% off, just based on which wideband you choose to use. I'd take the GM cal knowing that alone.

In the case of claiming the Rotofab works with the stock MAF cal...I'm dubious. I've seem some pretty outrageous claims for hardware that works with 'no tune', so without some data as proof I'd double check it with the stock stuff back to back. And definitely with the OE narrowbands rather than a wideband.

A wideband can be field-calibrated, in a way that a MAF can not ( Unless you have a 2000CFM flow bench ). You can use the 20.8% of free Oxygen in the atmosphere as a calibration point. Or, more correctly, the partial pressure of Oxygen, at whatever altitude you are at.

As long as you are using digital data transfer from the WB to the logger ( OBDII/CAN or serial ), if your WB displays the correct Oxygen% in "free-air" for your altitude, You should be good to go.

This is different from the common "free-air calibration", where you just force the WB to read 20.8% at whatever the pressure actually is.

A WB actually, does not measure AFR, lambda, or, even Oxygen% . It measures the partial pressure of Oxygen. So, it is affected by altitude, barometric pressure, temperature, and humidity; mostly, in that order. You can get really close with altitude/elevation, alone.

With a good calibration, a WB should read the following Oxygen%, with the sensor in open atmosphere ( "free-air" ), at a given altitude, plus or minus about 2% of the reading, to account for barometric pressure, temperature, humidity, and 1% variance of the sensor:

ELEVATION O2% reading +/- 0.2%
0'MSL 20.70%
500'MSL 20.56%
1000'MSL 20.42%
1500'MSL 20.28%
2000'MSL 20.14%
2500'MSL 20.00%
3000'MSL 19.86%
3500'MSL 19.72%
4000'MSL 19.58%
4500'MSL 19.44%
5000'MSL 19.30%
5500'MSL 19.16%
6000'MSL 19.02%
6500'MSL 18.88%
7000'MSL 18.74%
7500'MSL 18.60%
8000'MSL 18.46%
8500'MSL 18.32%
9000'MSL 18.18%
9500'MSL 18.04%
10000'MSL 17.90%

Assuming that you have a WB that can display O2% and DOES NOT REQUIRE FREE-AIR CALIBRATION ( which ruins the entire purpose, here ), if you see a reading that lines up with the above table, your O2 sensor is, almost, dead on. So, at least the WB, itself, knows the actual O2%, lambda, AFR, etc.

If you have digital data transfer from the WB to the logger ( either CANBus or serial ), you are good to go. If you are using analog voltage for data, there is some work to do, before it can be trusted. Here, ground offset issues are, usually, the source of errors.

Quote:

---

Originally Posted by dr.mike

A wideband can be field-calibrated, in a way that a MAF can not ( Unless you have a 2000CFM flow bench ). You can use the 20.8% of free Oxygen in the atmosphere as a calibration point. Or, more correctly, the partial pressure of Oxygen, at whatever altitude you are at.

As long as you are using digital data transfer from the WB to the logger ( OBDII/CAN or serial ), if your WB displays the correct Oxygen% in "free-air" for your altitude, You should be good to go.

This is different from the common "free-air calibration", where you just force the WB to read 20.8% at whatever the pressure actually is.

A WB actually, does not measure AFR, lambda, or, even Oxygen% . It measures the partial pressure of Oxygen. So, it is affected by altitude, barometric pressure, temperature, and humidity; mostly, in that order. You can get really close with altitude/elevation, alone.

With a good calibration, a WB should read the following Oxygen%, with the sensor in open atmosphere ( "free-air" ), at a given altitude, plus or minus about 2% of the reading, to account for barometric pressure, temperature, humidity, and 1% variance of the sensor:

ELEVATION O2% reading +/- 0.2%
0'MSL 20.70%
500'MSL 20.56%
1000'MSL 20.42%
1500'MSL 20.28%
2000'MSL 20.14%
2500'MSL 20.00%
3000'MSL 19.86%
3500'MSL 19.72%
4000'MSL 19.58%
4500'MSL 19.44%
5000'MSL 19.30%
5500'MSL 19.16%
6000'MSL 19.02%
6500'MSL 18.88%
7000'MSL 18.74%
7500'MSL 18.60%
8000'MSL 18.46%
8500'MSL 18.32%
9000'MSL 18.18%
9500'MSL 18.04%
10000'MSL 17.90%

Assuming that you have a WB that can display O2% and DOES NOT REQUIRE FREE-AIR CALIBRATION ( which ruins the entire purpose, here ), if you see a reading that lines up with the above table, your O2 sensor is, almost, dead on. So, at least the WB, itself, knows the actual O2%, lambda, AFR, etc.

If you have digital data transfer from the WB to the logger ( either CANBus or serial ), you are good to go. If you are using analog voltage for data, there is some work to do, before it can be trusted. Here, ground offset issues are, usually, the source of errors.

---

Thanks for the help. I have the AEM that emulates a can bus module, I think you can output the O2% but im not sure I will have to try it out. I also should put my stock airbox back in and check MAF like you suggested. When I put the wideband back in and "correct" the MAF calibration, it was off at most about 3% in the high Hz regions.

The AEM 30-0334 can be set to display o2%, its the menu functions. There is no PID of o2%, so, it just keeps outputting Lambda to the OBDII data channel.

Calibrate the MAF in whatever configuration that you plan to use it in.

If you know your fuel flow, and your air-to-fuel ratio, you know your air flow :)