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??

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.