Going MAFless (SD mode) - Clarification needed

[emarkay]

On a stock vehicle, (presuming WBO2's are installed), and aside from the slight intake restriction removal, are there any drivability advantages? I know it's a must for turbo and a good thing for radically altered engine components, but I was wondering, since WB's are coming down in price and PCM's are increasing in capability, what keeps the OEM's from just tossing the MAF all together?

MRK

[BowlingSS]

what keeps the OEM's from just tossing the MAF all together? MRK

That would be a cost saving right?? :exactly:

Bill

[SinisterSS]

Random thoughts with Jack Handy -

Primary reason for an automaker to use a MAF sensor - regulatory motivation in emissions & fuel economy. To achieve those, the MAF is key in the O2 feedback closed loop system.

If there were no regulatory requirements and gasoline was $0.50/gallon, we'd all still have 4-bbl carbs under the hood and would have no need for O2 or MAF sensors.

[emarkay]

Aw come on, on a stock and EPA registered application, a WB02 configured vehicle COULD achieve OBDIII standards, correct?

[hrodgmc]

I think atmospheric changes in the various U.S. climates are the primary reasons MAF's are retained.

[dfe1]

There are a couple reasons that MAFs are being used by OEMs-- initial certification and warranty. Part of the initial emissions certification testing includes starting a vehicle dead cold and running it under specific conditions. During this test, literally everything that comes out of the tailpipe is captured in large bags and analyzed. Once everything comes up to temperature and the catalytic converters light off, emissions fall to almost zero. But before that happens, the exhaust can be fairly dirty. One of the reasons a forward mounting position is favored for converters is that the closer they are to the engine, the quicker they light off. The quicker they light off, the lower the total emissions. At the same time, air/fuel ratios need to be controlled as tightly as possible to minimize emissions while the system is in open loop (before the O2 sensors warm up). A MAF-based system can make compensations automatically for variances in air flow under open loop, as well as closed loop control.

A second issue is warranty. Emissions control systems have to be warranteed for 8 years or 80,000 miles which means the manufacturer is on the hook even if there is no component failure, but a vehicle fails to pass an emisisons test. By having the ability to measure air flow, as opposed to calculating it, a MAF-based system can make adjustments to keep a vehicle emissions compliant. In the real world, increases in emissions caused by changes in air flow as an engine accumulates miles are rarely, if ever severe enough to cause an emissions test failure. But under the controlled conditions present during required long term testing, things are different. Even seemingly minor changes can be significant. If you're having trouble following the rationale, consider the gaping difference between EPA rated and actual fuel economy. And don't forget, your mileage may vary..., professional driver, closed course....

[emarkay]

Now that makes sense. Thanks.

[TAQuickness]

There are a couple reasons that MAFs are being used by OEMs-- initial certification and warranty. Part of the initial emissions certification testing includes starting a vehicle dead cold and running it under specific conditions. During this test, literally everything that comes out of the tailpipe is captured in large bags and analyzed. Once everything comes up to temperature and the catalytic converters light off, emissions fall to almost zero. But before that happens, the exhaust can be fairly dirty. One of the reasons a forward mounting position is favored for converters is that the closer they are to the engine, the quicker they light off. The quicker they light off, the lower the total emissions. At the same time, air/fuel ratios need to be controlled as tightly as possible to minimize emissions while the system is in open loop (before the O2 sensors warm up). A MAF-based system can make compensations automatically for variances in air flow under open loop, as well as closed loop control.

A second issue is warranty. Emissions control systems have to be warranteed for 8 years or 80,000 miles which means the manufacturer is on the hook even if there is no component failure, but a vehicle fails to pass an emisisons test. By having the ability to measure air flow, as opposed to calculating it, a MAF-based system can make adjustments to keep a vehicle emissions compliant. In the real world, increases in emissions caused by changes in air flow as an engine accumulates miles are rarely, if ever severe enough to cause an emissions test failure. But under the controlled conditions present during required long term testing, things are different. Even seemingly minor changes can be significant. If you're having trouble following the rationale, consider the gaping difference between EPA rated and actual fuel economy. And don't forget, your mileage may vary..., professional driver, closed course....

Throwing an anal $0.02 out there... The PCM never measures flow, it looks up data from the MAF table in respect to the incoming MAF Hz and calculates (interpolates) the mass flow value.

I think another reason the MAF is used is it offers a finer resolution to the air mass flow for finer tuning of emmisions standards.

[dfe1]

Throwing an anal $0.02 out there... The PCM never measures flow, it looks up data from the MAF table in respect to the incoming MAF Hz and calculates (interpolates) the mass flow value.

Isn't that measuring? The HZ value generated by the MAF sensor varies according to the amount of air flowing through the sensor. The conversion is simply from Hz to grams per second. That's really no different than an electric oil pressure gauge that converts a given voltage to psi except that the gauge does it all with hardware as opposed to a combination of hardware and software.

[TAQuickness]

Isn't that measuring? The HZ value generated by the MAF sensor varies according to the amount of air flowing through the sensor. The conversion is simply from Hz to grams per second. That's really no different than an electric oil pressure gauge that converts a given voltage to psi except that the gauge does it all with hardware as opposed to a combination of hardware and software.

It's close. In the same respect, MAF opperation is really no different (in fuctionality) than SD where the PCM takes MAP and RPM and looks up a value. The difference is the MAF calibration is a higher resolution than the VE table.

If the PCM was measuring, as opposed to calculating, there would be no need to re-calibrate the MAF when you mod the engine and/or induction plumbing, and a Corvette, Fbod, and Truck would all have the same MAF calibration tables (asusming they were all using the same size MAF).

The MAF calibration is a look up table respective to the stock components.

[dfe1]

I somewhat, kinda, almost agree with you, but I also somewhat, kinda almost disagree with you. The LS version of a MAF system does a lot of referencing and sanity checking. From what I've seen, it's actually a hybrid system that uses MAP and MAF readings in varying percentages. I don't know this for a fact, but I'm pretty sure that a lot of the sanity checking is included as a double check for electronic throttle control operation. The original GM MAF systems (1986-89) were pure MAF systems and no MAP sensor was included. LT1s also appear to use pure MAF systems with speed density being purely a back-up mode.

As with any air meter, eddies and reversion within the intake system can require application specific calibration-- that is, air may not flow the same way through a Corvete air filter/duct assembly as it does through a truck or F-body assembly. It would be interesting to check the accuracy of MAF air flow readings under controlled circumstances to see how much simply changing the filter/ducting altered MAF readings.

In spite of appearances, I'm not trying to make a big deal out of differences in terminology. I've just seen a lot of misinformation about MAF operation spread around and frankly, I'm not sure anyone (myself included) outside of a few GM engineers really knows how the system functions.

[John Skiba]

All measuring devices have "look up" tables or conversion tables. How does an temp sensor, oil pressure sensor, VSS sensor function? Some convert resistance values, some convert voltage values, some frequency. The MAF (Mass AirFlow Sensor) frequency output (LS1 at least) is converted in software (PCM) for flexibility of using the device in a wide range of application. One of the unknown variables as dfe1 mentioned which require the flexibility of a PCM lookup table being the air movement before and after the MAF due to ducting. If the manufacturer built the MAF with long tubes on each end to ensure consistant repeatable flow in all applications then it the output would be a fixed known. Such is not the case as the MAF is a small portable device which many times is placed before or after bends or in some cases right before a throttle body,etc.

Maybe we are all saying it in a slightly different way and I am missing something, but why would you not consider the MAF as a measuring device? Is it because it has a editable lookup table in the PCM?

[TAQuickness]

All measuring devices have "look up" tables or conversion tables. How does an temp sensor, oil pressure sensor, VSS sensor function? Some convert resistance values, some convert voltage values, some frequency. The MAF (Mass AirFlow Sensor) frequency output (LS1 at least) is converted in software (PCM) for flexibility of using the device in a wide range of application. One of the unknown variables as dfe1 mentioned which require the flexibility of a PCM lookup table being the air movement before and after the MAF due to ducting. If the manufacturer built the MAF with long tubes on each end to ensure consistant repeatable flow in all applications then it the output would be a fixed known. Such is not the case as the MAF is a small portable device which many times is placed before or after bends or in some cases right before a throttle body,etc.

Maybe we are all saying it in a slightly different way and I am missing something, but why would you not consider the MAF as a measuring device? Is it because it has a editable lookup table in the PCM?


The MAF is a measuring device, as is a MAP sensor. The PCM does not measure anything. PCM only looks up values. And I agree, if the MAF was installed with the proper plumbing, there wouldn't be much of an issue with the calibration tables.

I'm just splitting well split hairs :D

[John Skiba]

:moon1: :cheers: