mass air flow sensor>theory of operation
07-27-2005, 12:38 PM
#1
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Join Date: Apr 2004
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mass air flow sensor>theory of operation
This is an informative article that was posted on EFI University's site. NOT witten by me.
KingBarry79
Joined: 04 Oct 2004
Posts: 40
Location: Maryland
Posted: Tue Apr 12, 2005 04:01 pm Post subject: Maf Basics 101
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For some of you this will be new and interesting information, for others it will be a review. I hope that it is atleast a semi-complete listing of MAF function for everyone to read. A lot of this information was gathered in my several years as an engine management tuner. I also have to thank Spiro Gounaropolos, Jerry Wroblewski, Don LaSota, and Brian Herron as they have been an invaluable source of info.
The MAF sensor measures the air coming into the engine by means of a heated wire that is cooled by the incoming air in the MAF sable tube. The MAF circuitry applies more voltage to keep the wire at a constant temperature. The MAF circuitry measures this voltage. This in turn tells the PCM how much air is flowing into the engine which then calculates engine load and controls injector pulsewidth.
The MAF curve is essentially the plot between units of MAF voltage and the mass of the air flowing into the engine. The MAF curve is the most important parameter used when tuning an engine. If the MAF curve is not right, then fuel will be wrong as well as spark. Spark is calculated based on load – and load data comes from data gathered from the MAF.
With speed density A/F was calculated and commanded via a VE table. On a Speed Density vehicle if the VE table was set up wrong the A/F would be incorrect and the vehicle would be either rich or lean when compared to your commanded A/F. To make things simple; on a vehicle equipped with a MAF, the MAF Signal can be looked at as the VE Table Lookup in a speed density vehicle. If the MAF Curve is set up incorrectly, the vehicle will have the wrong AFR when compared to the commanded A/F.
The terms load and volumetric efficiency can be used interchangeably. It is usually expressed in a percentage, such as 50% load. Load of volumetric efficiency is actually the measurement of how much air if flowing into the engine. If a 4.6L engine sucks in 4.6L of air in two engine revolutions (it takes two engine revolutions for all the cylinders to fill) then the load is 100%. If it only inhales 2.3L of air, then the load is 2.3/4.6 or 50%. On a blown car you can force more air into the engine that it’s actually displacement, so in these cases, load will go above 100%
If you command a 12:1 air/fuel for WOT in the base fuel table, you will adjust the MAF transfer function until you achieve the 12:1 air/fuel ratio. By calibrating the MAF Function in this way, you will now have the correct engine load and a mass air meter that is working correctly. Because the mass air meter is now working correctly the car will be capable of adjusting the air/fuel ration on its own as air density changes. To calculate a MAF correction factor, or the amount you need to adjust the air meter transfer function by, you divide the commanded A/F into the actual A/F ratio (actual/commanded). The result is the correction factor. You can only get this info from a wideband and PCM datalogging.
DEEP BREATH!
The best scenario is to have a MAF that will not peg. Pegging means that the MAF has reached its maximum capacity, it can physically still flow more air, but the electronics will not measure it. A MAF will output to battery voltage, but most PCM’s will only acknowledge to 5v. The PCM in this case will think the air coming in the engine is staying the same (5v to 12v+) so it will not add more fuel, but more air will be entering the engine, causing a possible lean condition. Additionally, the load calculations after the MAF pegs will be off.
Quick Notes:
Try to use a MAF that only uses 80-90% of its range. This allows for the best resolution in the lower RPM levels. A suck through maf is usually best for blower cars. Suck through aka Draw through setups are usually easier to tune, and will always require less range from the MAF sensor. You have a blow-through setup it will peg sooner then the same combination in a draw-through setup.
_________________
Just about any tuner can make you go fast, but can they get your car to behave in traffic?
EFI101 Grad
Jason King
KingBarry79
Joined: 04 Oct 2004
Posts: 40
Location: Maryland
Posted: Tue Apr 12, 2005 04:01 pm Post subject: Maf Basics 101
--------------------------------------------------------------------------------
For some of you this will be new and interesting information, for others it will be a review. I hope that it is atleast a semi-complete listing of MAF function for everyone to read. A lot of this information was gathered in my several years as an engine management tuner. I also have to thank Spiro Gounaropolos, Jerry Wroblewski, Don LaSota, and Brian Herron as they have been an invaluable source of info.
The MAF sensor measures the air coming into the engine by means of a heated wire that is cooled by the incoming air in the MAF sable tube. The MAF circuitry applies more voltage to keep the wire at a constant temperature. The MAF circuitry measures this voltage. This in turn tells the PCM how much air is flowing into the engine which then calculates engine load and controls injector pulsewidth.
The MAF curve is essentially the plot between units of MAF voltage and the mass of the air flowing into the engine. The MAF curve is the most important parameter used when tuning an engine. If the MAF curve is not right, then fuel will be wrong as well as spark. Spark is calculated based on load – and load data comes from data gathered from the MAF.
With speed density A/F was calculated and commanded via a VE table. On a Speed Density vehicle if the VE table was set up wrong the A/F would be incorrect and the vehicle would be either rich or lean when compared to your commanded A/F. To make things simple; on a vehicle equipped with a MAF, the MAF Signal can be looked at as the VE Table Lookup in a speed density vehicle. If the MAF Curve is set up incorrectly, the vehicle will have the wrong AFR when compared to the commanded A/F.
The terms load and volumetric efficiency can be used interchangeably. It is usually expressed in a percentage, such as 50% load. Load of volumetric efficiency is actually the measurement of how much air if flowing into the engine. If a 4.6L engine sucks in 4.6L of air in two engine revolutions (it takes two engine revolutions for all the cylinders to fill) then the load is 100%. If it only inhales 2.3L of air, then the load is 2.3/4.6 or 50%. On a blown car you can force more air into the engine that it’s actually displacement, so in these cases, load will go above 100%
If you command a 12:1 air/fuel for WOT in the base fuel table, you will adjust the MAF transfer function until you achieve the 12:1 air/fuel ratio. By calibrating the MAF Function in this way, you will now have the correct engine load and a mass air meter that is working correctly. Because the mass air meter is now working correctly the car will be capable of adjusting the air/fuel ration on its own as air density changes. To calculate a MAF correction factor, or the amount you need to adjust the air meter transfer function by, you divide the commanded A/F into the actual A/F ratio (actual/commanded). The result is the correction factor. You can only get this info from a wideband and PCM datalogging.
DEEP BREATH!
The best scenario is to have a MAF that will not peg. Pegging means that the MAF has reached its maximum capacity, it can physically still flow more air, but the electronics will not measure it. A MAF will output to battery voltage, but most PCM’s will only acknowledge to 5v. The PCM in this case will think the air coming in the engine is staying the same (5v to 12v+) so it will not add more fuel, but more air will be entering the engine, causing a possible lean condition. Additionally, the load calculations after the MAF pegs will be off.
Quick Notes:
Try to use a MAF that only uses 80-90% of its range. This allows for the best resolution in the lower RPM levels. A suck through maf is usually best for blower cars. Suck through aka Draw through setups are usually easier to tune, and will always require less range from the MAF sensor. You have a blow-through setup it will peg sooner then the same combination in a draw-through setup.
_________________
Just about any tuner can make you go fast, but can they get your car to behave in traffic?
EFI101 Grad
Jason King
07-27-2005, 05:22 PM
#2
Jack Of All Trades
Join Date: Jun 2004
Location: Acton, California
Posts: 2,296
That's an interesting write-up............. 
If you're interested in how all of the components work together, buy the "Bosch Fuel Injection & Engine Management Book". Very interesting reading. Every fuel injection system in the world is based around the original Robert Bosch designs.............. lol.... just like every turbocharger brand in the world is based around the original Garrett designs.
BTW - That is one thing the hondus and other vehicles have that is better than what we have, and that's an air flow measurement system based around "manifold absolute pressure" (MAP sensor) versus out MAF system. They're much easier to tune with.
If you're interested in how all of the components work together, buy the "Bosch Fuel Injection & Engine Management Book". Very interesting reading. Every fuel injection system in the world is based around the original Robert Bosch designs.............. lol.... just like every turbocharger brand in the world is based around the original Garrett designs.
BTW - That is one thing the hondus and other vehicles have that is better than what we have, and that's an air flow measurement system based around "manifold absolute pressure" (MAP sensor) versus out MAF system. They're much easier to tune with.
Last edited by CanyonCarver; 07-27-2005 at 05:35 PM.
07-28-2005, 11:10 PM
#4
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Join Date: Jun 2003
Location: Wilmington, NC
Posts: 650
MAP's are great... Honda's are so much easier to tune, due to that fact that they have MAP, as opposed to MAF.
And you could still run ITB's... How do you think RB26DETT's run ITB's? Basically, you have a Surge Tank surrounding each Throttle Body, so you could still run Intake Piping, with a MAF integrated into the design. Hell, with the design that I've come up with, you could even run a Single Turbo set-up with the Surge Tanked ITB's.
Although, with our Honda race car that we performed the ITB modification on, we had to tune it to Hell and back. It was running extremely rich until about 60% power... Then it ran like an absolute dream, and screamed like a school girl looking at a dead body.
Only about an 18bhp increase though... Not too good considering there are aftermarket manifolds that add more than that, and they're still single piece.
Anyway, I'll post up my designs on the ITB's once I at least mail them to myself (Postage date stamp can't be forged... Proving the idea was mine on, or before that date
). It's an interesting idea to ponder, but it would be an outragous project... Not one I plan on taking on any time soon.
And you could still run ITB's... How do you think RB26DETT's run ITB's? Basically, you have a Surge Tank surrounding each Throttle Body, so you could still run Intake Piping, with a MAF integrated into the design. Hell, with the design that I've come up with, you could even run a Single Turbo set-up with the Surge Tanked ITB's.
Although, with our Honda race car that we performed the ITB modification on, we had to tune it to Hell and back. It was running extremely rich until about 60% power... Then it ran like an absolute dream, and screamed like a school girl looking at a dead body.
Only about an 18bhp increase though... Not too good considering there are aftermarket manifolds that add more than that, and they're still single piece.
Anyway, I'll post up my designs on the ITB's once I at least mail them to myself (Postage date stamp can't be forged... Proving the idea was mine on, or before that date
). It's an interesting idea to ponder, but it would be an outragous project... Not one I plan on taking on any time soon.
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