Why do engines with a MAF sensor still use an o2 sensor?

[ELS]

Hot wire MAF sensor is based on heat transfer/dissipation. That is mass not velocity nor volume.

Mass is directly related to volume.

Not so. Just google it. Wikipedia is good.

Tell me how much mass does 0 volume of air have?
If you feel like changing the topic just to tell everyone something, at least be right and don't use wikipedia as your source.

[Schurkey]

SOME sensors provide "gross" inputs for the computer to calculate fuel delivery: For example, engine coolant temp, throttle position, MAP, MAF.

The O2 sensor provides a method to "fine-tune" the fuel delivery, some amount of self-learning via the short- and long-term fuel trims.

EGR displaces incoming air. The computer knows when the EGR is operational, the "gross" fueling changes are already incorporated into those fuel tables. Again, the O2 provides "fine tuning" of the fuel delivery.

O2 sensor(s) are essential for closed-loop operation.

[ELS]

SOME sensors provide "gross" inputs for the computer to calculate fuel delivery: For example, engine coolant temp, throttle position, MAP, MAF.

The O2 sensor provides a method to "fine-tune" the fuel delivery, some amount of self-learning via the short- and long-term fuel trims.

EGR displaces incoming air. The computer knows when the EGR is operational, the "gross" fueling changes are already incorporated into those fuel tables. Again, the O2 provides "fine tuning" of the fuel delivery.

O2 sensor(s) are essential for closed-loop operation.

How is the EGR flow calculated? is there like another MAF or a pressure sensor in the exhaust?

[Schurkey]

How is the EGR flow calculated? is there like another MAF or a pressure sensor in the exhaust?

SOME applications have an EGR position sensor. Lots of older stuff does not. There's no precise method of calculating EGR flow on those, and even the ones with a position sensor rely on the passages being clear--not coked-up with carbon.

But again--EGR introduces almost zero oxygen, and the O2 sensor will trim the fuel delivery to provide the approved air/fuel ratio with or without EGR (within the limits of the system correction capability.)

[Bill Chase]

Can't you just calculate the required injector duty cycle depending on the MAF reading?

Also, wouldn't EGR mess up the reading of an O2 sensor?

The maf can tell the ECU how much air is entering, and even modulate fuel accordingly, but it can't tell you if that fuel is being burned completely, or if you have a misfire. As others have said.. it's a system no single sensor dominates what the ECU is doing at any point in time, if that were true we'd have a tps and alpha n systems still

[Bill Chase]

SOME sensors provide "gross" inputs for the computer to calculate fuel delivery: For example, engine coolant temp, throttle position, MAP, MAF.

The O2 sensor provides a method to "fine-tune" the fuel delivery, some amount of self-learning via the short- and long-term fuel trims.

EGR displaces incoming air. The computer knows when the EGR is operational, the "gross" fueling changes are already incorporated into those fuel tables. Again, the O2 provides "fine tuning" of the fuel delivery.

O2 sensor(s) are essential for closed-loop operation.

How is the EGR flow calculated? is there like another MAF or a pressure sensor in the exhaust?

My guess is when the OEM gets each engine platform certified for car, light truck, heavy duty, export etc it is days spent on an engine Dyno, then chassis Dyno dialing it in for each engine, transmission, vehicle combination. If you take a look at the tune file of the same engine, same year, but different application/chassis/exhaust system.. you will see significantly different EGR system settings. At least this is true for late 80's, early 90's gm sbc stuff. Camshaft used will also significantly impact the EGR system settings.

[dannobee]

EGR is inert, that is, it won't burn again. It lacks both fuel and oxygen. As such, the egr flow doesn't affect the O2 sensor reading. And sure, someone will say a bad/burned gasket can allow air into the system, and sure, that's true, but in a properly functioning system, an open egr valve will have little or no effect on the oxygen sensor reading. The various sensors used to monitor egr over the years (valve position sensor, egr temp sensor, etc) proves that statement; if it was possible to monitor egr volume by using the O2 sensor, the OEM's would have done it.

And remember, EGR was around long before oxygen sensors. And with carburetors, no less.

[Tuner]

EGR is inert, that is, it won't burn again. It lacks both fuel and oxygen. As such, the egr flow doesn't affect the O2 sensor reading. And sure, someone will say a bad/burned gasket can allow air into the system, and sure, that's true, but in a properly functioning system, an open egr valve will have little or no effect on the oxygen sensor reading. The various sensors used to monitor egr over the years (valve position sensor, egr temp sensor, etc) proves that statement; if it was possible to monitor egr volume by using the O2 sensor, the OEM's would have done it.

And remember, EGR was around long before oxygen sensors. And with carburetors, no less.

"EGR is inert, that is, it won't burn again. It lacks both fuel and oxygen."

This isn't so. EGR from lean combustion contains O2, and bonus, it is hot O2, so the hot exhaust gas will not only improve vaporization it will improve combustion.

The first EGR systems in '73 were crude and the emissions calibration engineers hadn't figured out how to use the hot exhaust to advantage, so nearly all new cars ran better when EGR was disabled. This created the situation of misguided urban lore and prejudice against EGR which is now going on 50 years old.

In '78 and '79 the emissions engineers started getting EGR figured out and some engines started appearing that didn't respond favorably at all to disconnecting or blocking the EGR. Disconnecting the EGR on some Pontiac 455 and Olds 403 engines would almost double fuel consumption. 302 Ford was another that liked its EGR at part-throttle, but the mileage deal was not as dramatic as the Olds and Pontiac.

Some engines with radical cams that have a lot of valve timing overlap will respond to lean A/F in high vacuum cruising conditions for the same reason, hot oxygen in high vacuum exhaust reversion improves combustion. Exhaust system resonance has large influence on whether or not and to the degree this favorable phenomenon occurs. Just changing the muffler(s) can have a huge influence on carb calibration in high vacuum cruising conditions. Vacuum advance calibration is also important and can be sensitive to small changes in advance per inch Hg. If you don't think clean plugs and minimum fuel consumption are important, don't bother.

In the case of valve timing overlap combined with intake and exhaust system resonance resulting in a large amount of intake air passing through into the exhaust, the O2 sensor will see O2 that has not been involved in combustion and will report a leaner A/F than the actual combustion A/F. When a radical engine responds favorably to indicated A/F leaner than 17/1 overlap bypass is probably occurring, so the O2 sensor reading must be taken with a grain of salt, but because tuning is a process of judgement calls in seeking best performance, numbers on a gauge are irrelevant for anything but reference anyway.

[ELS]

EGR is inert, that is, it won't burn again. It lacks both fuel and oxygen. As such, the egr flow doesn't affect the O2 sensor reading. And sure, someone will say a bad/burned gasket can allow air into the system, and sure, that's true, but in a properly functioning system, an open egr valve will have little or no effect on the oxygen sensor reading. The various sensors used to monitor egr over the years (valve position sensor, egr temp sensor, etc) proves that statement; if it was possible to monitor egr volume by using the O2 sensor, the OEM's would have done it.

And remember, EGR was around long before oxygen sensors. And with carburetors, no less.

"EGR is inert, that is, it won't burn again. It lacks both fuel and oxygen."

This isn't so. EGR from lean combustion contains O2, and bonus, it is hot O2, so the hot exhaust gas will not only improve vaporization it will improve combustion.

The first EGR systems in '73 were crude and the emissions calibration engineers hadn't figured out how to use the hot exhaust to advantage, so nearly all new cars ran better when EGR was disabled. This created the situation of misguided urban lore and prejudice against EGR which is now going on 50 years old.

In '78 and '79 the emissions engineers started getting EGR figured out and some engines started appearing that didn't respond favorably at all to disconnecting or blocking the EGR. Disconnecting the EGR on some Pontiac 455 and Olds 403 engines would almost double fuel consumption. 302 Ford was another that liked its EGR at part-throttle, but the mileage deal was not as dramatic as the Olds and Pontiac.

Some engines with radical cams that have a lot of valve timing overlap will respond to lean A/F in high vacuum cruising conditions for the same reason, hot oxygen in high vacuum exhaust reversion improves combustion. Exhaust system resonance has large influence on whether or not and to the degree this favorable phenomenon occurs. Just changing the muffler(s) can have a huge influence on carb calibration in high vacuum cruising conditions. Vacuum advance calibration is also important and can be sensitive to small changes in advance per inch Hg. If you don't think clean plugs and minimum fuel consumption are important, don't bother.

In the case of valve timing overlap combined with intake and exhaust system resonance resulting in a large amount of intake air passing through into the exhaust, the O2 sensor will see O2 that has not been involved in combustion and will report a leaner A/F than the actual combustion A/F. When a radical engine responds favorably to indicated A/F leaner than 17/1 overlap bypass is probably occurring, so the O2 sensor reading must be taken with a grain of salt, but because tuning is a process of judgement calls in seeking best performance, numbers on a gauge are irrelevant for anything but reference anyway.

yeah
If EGR being 'innert' means it wont affect the O2 sensor reading. Think of what the O2 sensor is reading... Exhaust Gasses.
It will affect the reading because it "dilutes" the oxygen content so the O2 sensor thinks the engine is running richer than it actually is, because there's exhaust gases that displace the real mixture exhaust gases.

Well I've seen EGR systems on MUCH earlier engines, think of early flat-heat engines where the intake was a log intake right on top of a log exhaust manifold, and would have a sizeable passage going from the exhaust to the intake.
I presume this was done to instead heat the intake mixture for better evaporization, but it is also adding EGR.

[Tuner]

EGR is inert, that is, it won't burn again. It lacks both fuel and oxygen. As such, the egr flow doesn't affect the O2 sensor reading. And sure, someone will say a bad/burned gasket can allow air into the system, and sure, that's true, but in a properly functioning system, an open egr valve will have little or no effect on the oxygen sensor reading. The various sensors used to monitor egr over the years (valve position sensor, egr temp sensor, etc) proves that statement; if it was possible to monitor egr volume by using the O2 sensor, the OEM's would have done it.

And remember, EGR was around long before oxygen sensors. And with carburetors, no less.

"EGR is inert, that is, it won't burn again. It lacks both fuel and oxygen."

This isn't so. EGR from lean combustion contains O2, and bonus, it is hot O2, so the hot exhaust gas will not only improve vaporization it will improve combustion.

The first EGR systems in '73 were crude and the emissions calibration engineers hadn't figured out how to use the hot exhaust to advantage, so nearly all new cars ran better when EGR was disabled. This created the situation of misguided urban lore and prejudice against EGR which is now going on 50 years old.

In '78 and '79 the emissions engineers started getting EGR figured out and some engines started appearing that didn't respond favorably at all to disconnecting or blocking the EGR. Disconnecting the EGR on some Pontiac 455 and Olds 403 engines would almost double fuel consumption. 302 Ford was another that liked its EGR at part-throttle, but the mileage deal was not as dramatic as the Olds and Pontiac.

Some engines with radical cams that have a lot of valve timing overlap will respond to lean A/F in high vacuum cruising conditions for the same reason, hot oxygen in high vacuum exhaust reversion improves combustion. Exhaust system resonance has large influence on whether or not and to the degree this favorable phenomenon occurs. Just changing the muffler(s) can have a huge influence on carb calibration in high vacuum cruising conditions. Vacuum advance calibration is also important and can be sensitive to small changes in advance per inch Hg. If you don't think clean plugs and minimum fuel consumption are important, don't bother.

In the case of valve timing overlap combined with intake and exhaust system resonance resulting in a large amount of intake air passing through into the exhaust, the O2 sensor will see O2 that has not been involved in combustion and will report a leaner A/F than the actual combustion A/F. When a radical engine responds favorably to indicated A/F leaner than 17/1 overlap bypass is probably occurring, so the O2 sensor reading must be taken with a grain of salt, but because tuning is a process of judgement calls in seeking best performance, numbers on a gauge are irrelevant for anything but reference anyway.

yeah
If EGR being 'innert' means it wont affect the O2 sensor reading. Think of what the O2 sensor is reading... Exhaust Gasses.
It will affect the reading because it "dilutes" the oxygen content so the O2 sensor thinks the engine is running richer than it actually is, because there's exhaust gases that displace the real mixture exhaust gases.

Well I've seen EGR systems on MUCH earlier engines, think of early flat-heat engines where the intake was a log intake right on top of a log exhaust manifold, and would have a sizeable passage going from the exhaust to the intake.
I presume this was done to instead heat the intake mixture for better evaporization, but it is also adding EGR.

It is evident you misunderstand what you have seen on the old flathead engines. The exhaust gas only heats the intake manifold for vaporization, it does not actually mix with the intake air.

For the intent and purpose of production engine management, O2 sensors only measure O2, whether it is in fresh air or exhaust gas makes no difference, O2 is O2.

Some engine management systems have O2 sensors in the intake manifold to measure O2 content to compensate for dilution after EGR is added.

[Schurkey]

It will affect the reading because it "dilutes" the oxygen content so the O2 sensor thinks the engine is running richer than it actually is, because there's exhaust gases that displace the real mixture exhaust gases.

This is your basic mistake in logic.

Any dilution of the intake charge with inert material is automatically compensated-for via the MAP, MAF, and throttle-position sensors. You're moving the throttle to get the power you need--which affects mass flow, intake pressure, and throttle position.

The inert EGR affects nothing so far as the O2 sensor is concerned. It's still reading the O2 in the exhaust stream, it doesn't know the difference between "fresh" exhaust and "recirculated" exhaust, and it's still fine-tuning the fuel delivery to make the O2 voltage swing from high to low to high, exactly as the engineers intend; therefore the mixture is essentially at the air/fuel ratio the engineers intend.

[ELS]

It will affect the reading because it "dilutes" the oxygen content so the O2 sensor thinks the engine is running richer than it actually is, because there's exhaust gases that displace the real mixture exhaust gases.

This is your basic mistake in logic.

Any dilution of the intake charge with inert material is automatically compensated-for via the MAP, MAF, and throttle-position sensors. You're moving the throttle to get the power you need--which affects mass flow, intake pressure, and throttle position.

The inert EGR affects nothing so far as the O2 sensor is concerned. It's still reading the O2 in the exhaust stream, it doesn't know the difference between "fresh" exhaust and "recirculated" exhaust, and it's still fine-tuning the fuel delivery to make the O2 voltage swing from high to low to high, exactly as the engineers intend; therefore the mixture is essentially at the air/fuel ratio the engineers intend.

Ok I think you're right that the reading will be the same but not for the reason you described.

If EGR is added, the fuel and air intake stays the same so it's a closed loop, the oxygen content will not change because there just isnt enough fuel to burn any more oxygen.
Even if it burns some of the oxygen from the EGR gas, it will just burn less of the clean air coming in.

[07GTS]

there is usually a system in place for anything that offsets the closed loop control, the use of the fuel trims STFT and LTFT have modes built in for when the tank purge is opened to the manifold to adjust to the added fuel vapor entering, so i can only assume that the egr will have its own setup like that, and they are usually only used under curtain conditions as well in the first place

[barnym17]

SOME sensors provide "gross" inputs for the computer to calculate fuel delivery: For example, engine coolant temp, throttle position, MAP, MAF.

The O2 sensor provides a method to "fine-tune" the fuel delivery, some amount of self-learning via the short- and long-term fuel trims.

EGR displaces incoming air. The computer knows when the EGR is operational, the "gross" fueling changes are already incorporated into those fuel tables. Again, the O2 provides "fine tuning" of the fuel delivery.

O2 sensor(s) are essential for closed-loop operation.

How is the EGR flow calculated? is there like another MAF or a pressure sensor in the exhaust?

In the big truck world egr flow is measured and clogged passages sure cause running issues.

[dannobee]

I stick by my statement; EGR is inert, it has no affect on the amount of oxygen in the exhaust. Look no further than your 5 gas exhaust analyzer. With the probe out of the exhaust, 20.7% oxygen, with the probe inside the exhaust, 0.3% oxygen. Where is this "other" oxygen of which you speak coming from? Hint, it's simply not there.

With respect to "Hot O2," you do realize that EGR COOLS the combustion process, right? Because the main purpose of EGR is to reduce oxides of nitrogen emissions formed by high combustion temperatures. Ideal gas laws (Charles's Law, to be exact) are not germane to this discussion.

And if you somehow think that disconnecting the EGR valve from a properly running system would increase mileage, you lack the basic understanding of pumping losses and the effect of introducing an inert gas into the intake charge of an engine. Conduct the experiment for yourself. Go disconnect the EGR system on your daily driver and compare the mileage before and after.

Diesel EGR is entirely different because Diesels don't require a homogeneous fuel air mixture for the flame front. And where is the oxygen sensor on a Diesel?