MAF/MAP/AFS/AFM
03-09-2003, 02:27 AM
#1
Three Wheelin'
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MAF/MAP/AFS/AFM
So when exactly did the Air Flow Meter became the mass air flow sensor? I'm just bored and ranting but every so often an auction comes up on ebay offering a Mass Air Flow Sensor and what appears? A standard barn door flapper air flow meter. So, is it me or is the true MAF/MAP the hot wire or pressure sensor type? <img border="0" alt="[offtopic]" title="" src="graemlins/offtopic.gif" />
03-09-2003, 03:43 AM
#2
Race Director
Yes, you're right, people get the terms mixed up:
AFM - air-flow meter, measures flow (volume), not mass and requires air-temp and altitude sensors to calculate a compensation to arrive at mass
MAF - mass air-flow meter, measures air mass going through it, doesn't need altitude sensor and only requires air-temp for cold-start enrichment
MAP - manifold absolute pressure sensor, measures pressure and calculates an air mass. Can compensate for VE-volumetric efficiency; what actually makes it into the engine vs. what's flowing way out at the air cleaner. Is standard for all advanced aftermarket EFI systems.
AFM - air-flow meter, measures flow (volume), not mass and requires air-temp and altitude sensors to calculate a compensation to arrive at mass
MAF - mass air-flow meter, measures air mass going through it, doesn't need altitude sensor and only requires air-temp for cold-start enrichment
MAP - manifold absolute pressure sensor, measures pressure and calculates an air mass. Can compensate for VE-volumetric efficiency; what actually makes it into the engine vs. what's flowing way out at the air cleaner. Is standard for all advanced aftermarket EFI systems.
03-09-2003, 11:07 AM
#3
Race Director
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Danno:
<strong>Yes, you're right, people get the terms mixed up:
AFM - air-flow meter, measures flow (volume), not mass and requires air-temp and altitude sensors to calculate a compensation to arrive at mass
MAF - mass air-flow meter, measures air mass going through it, doesn't need altitude sensor and only requires air-temp for cold-start enrichment
MAP - manifold absolute pressure sensor, measures pressure and calculates an air mass. Can compensate for VE-volumetric efficiency; what actually makes it into the engine vs. what's flowing way out at the air cleaner. Is standard for all advanced aftermarket EFI systems.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I'd like to add that while you can compensate for VE with a MAP, a MAF is superior in this regard. A hot wire MAF will automatically compensate for changes in VE since it more or less directly measures air mass which is what we really want to know. Changing cams? No sweat for a MAF. Adding CAI or header with a MAF? No sweat. Have a turbocharged car and changing boost or even turbos? No sweat for a MAF equipped car as long as the flow does not go beyond the capability of the particular MAF.
Note: changing a turbo or large changes in boost will still require remapping in most cases since you will be changing combustion chamber pressures and temps.
<strong>Yes, you're right, people get the terms mixed up:
AFM - air-flow meter, measures flow (volume), not mass and requires air-temp and altitude sensors to calculate a compensation to arrive at mass
MAF - mass air-flow meter, measures air mass going through it, doesn't need altitude sensor and only requires air-temp for cold-start enrichment
MAP - manifold absolute pressure sensor, measures pressure and calculates an air mass. Can compensate for VE-volumetric efficiency; what actually makes it into the engine vs. what's flowing way out at the air cleaner. Is standard for all advanced aftermarket EFI systems.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I'd like to add that while you can compensate for VE with a MAP, a MAF is superior in this regard. A hot wire MAF will automatically compensate for changes in VE since it more or less directly measures air mass which is what we really want to know. Changing cams? No sweat for a MAF. Adding CAI or header with a MAF? No sweat. Have a turbocharged car and changing boost or even turbos? No sweat for a MAF equipped car as long as the flow does not go beyond the capability of the particular MAF.
Note: changing a turbo or large changes in boost will still require remapping in most cases since you will be changing combustion chamber pressures and temps.
03-09-2003, 02:09 PM
#4
Race Director
How can a MAF even sense VE? It's measuring only air at atmospheric density at the end of the pipe. I think you're talking about measuring the changes in volume of flow. After you stretch out the air-column the intake, it's a different volume and density. The air by that point has already been measured by a MAF.
"changes in VE since it more or less directly measures air mass"
VE is not the same as total air mass. You can be sucking the same mass of air, yet be at a VE of .50 or .75.
"changes in VE since it more or less directly measures air mass"
VE is not the same as total air mass. You can be sucking the same mass of air, yet be at a VE of .50 or .75.
03-09-2003, 08:14 PM
#5
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The VAF and MAF are used for directly measuring Ve because they measure the amount of air (volume or mass) that the engine is currently consuming. Divide that value by the theoretical amount (volume or mass) based on rpm and displacement and you get Ve in real time. This all assumes no leaks in the intake tract which is the main reason leaks adversely affect VAF and MAF systems. Forget about the affect of any turbos, heat or restrictions in the intake plumbing. With the meter at the very entrance to the intake, it directly measures the efficiency of the engine (again assume no leaks).
03-09-2003, 10:31 PM
#7
Race Director
" Divide that value by the theoretical amount (volume or mass) based on rpm and displacement and you get Ve in real time."
This is kinda like the Hiesenberg principle at work here. You can't have real-time because you need to let some elapse time occur in order to measure RPM.
"With the meter at the very entrance to the intake, it directly measures the efficiency of the engine (again assume no leaks)."
But the air that's measured at the entrance is not the same piece of air that's going into the engine, which has a different density (VE). By the time the measured air makes it to the engine, its VE could be very different from the VE when its mass/volume was measured. This is the cause of the flaming exhausts on shifts; the AFM/MAF measures 2.5L of air flowed in X-amount of time, yet simultaneously the closed throttle stretches the air that entered earlier yielding a VE of 0.20 or 0.5L ingested by the engine in the same X-amount of time. You have to wait a while until the air-column has stopped moving before the VE changes are reflected at the entrance of the intake tract. Now if we place the MAF sensor after the throttle-body, then it can measure VE instantaneously in real-time.
This is kinda like the Hiesenberg principle at work here. You can't have real-time because you need to let some elapse time occur in order to measure RPM.
"With the meter at the very entrance to the intake, it directly measures the efficiency of the engine (again assume no leaks)."
But the air that's measured at the entrance is not the same piece of air that's going into the engine, which has a different density (VE). By the time the measured air makes it to the engine, its VE could be very different from the VE when its mass/volume was measured. This is the cause of the flaming exhausts on shifts; the AFM/MAF measures 2.5L of air flowed in X-amount of time, yet simultaneously the closed throttle stretches the air that entered earlier yielding a VE of 0.20 or 0.5L ingested by the engine in the same X-amount of time. You have to wait a while until the air-column has stopped moving before the VE changes are reflected at the entrance of the intake tract. Now if we place the MAF sensor after the throttle-body, then it can measure VE instantaneously in real-time.
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03-09-2003, 10:38 PM
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</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Danno:
<strong>This is the cause of the flaming exhausts on shifts;.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I thought that was caused by a "on the fly" timing adjust that leaves the exhaust open longer and delays the spark so part of the combustion happens in the turbo itself thus keeping it spooled while letting off the throttle or shifting.
or is that just in the "big boy's" cars?
<strong>This is the cause of the flaming exhausts on shifts;.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I thought that was caused by a "on the fly" timing adjust that leaves the exhaust open longer and delays the spark so part of the combustion happens in the turbo itself thus keeping it spooled while letting off the throttle or shifting.
or is that just in the "big boy's" cars?
03-09-2003, 10:44 PM
#9
Race Director
That's the 'anti-lag' feature you're talking about. A couple of aftermarket EFI systems allow you to program in extra fuel and extra ignition retard at low MAP-pressure/high-RPM values. This in intentional. I'm pointing out the flaming exhausts you get when removing the cat and increasing the boost on cars with AFM & MAF sensors.
If you hook up a scope and record manifold-pressure, AFM/MAF output and injector duty-cycle, you'll see there's a fraction of a second between when the manifold drops pressure from the closed throttle-plate on shifts and when the AFM/MAF sensor actually senses this and cuts the injectors.
If you hook up a scope and record manifold-pressure, AFM/MAF output and injector duty-cycle, you'll see there's a fraction of a second between when the manifold drops pressure from the closed throttle-plate on shifts and when the AFM/MAF sensor actually senses this and cuts the injectors.
03-09-2003, 10:50 PM
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so what your saying is that a map or maf placed on the engine side of the throttle body is the way to go... or am I missing the point.
03-09-2003, 11:19 PM
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</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> You can't have real-time because you need to let some elapse time occur in order to measure RPM </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Motronic updates RPM every 11.5 msec for the 944/951, if that is not real time enough I don't know what will be (~87 updates/sec). It updates the VAF reading anywhere from 25 to 50 times/sec (it's not a timed event like RPM).
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> But the air that's measured at the entrance is not the same piece of air that's going into the engine, which has a different density (VE). </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Ve is not density, it is the ratio of actual ingested volume divided by theoretical volume which is directly related to pressure. The air measured is not the same piece actually entering the combustion chamber, but the particular piece doesn't matter it is the flow which is registered at the flow meter at the start of the intake tract that matters.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> you'll see there's a fraction of a second between when the manifold drops pressure from the closed throttle-plate on shifts and when the AFM/MAF sensor actually senses this and cuts the injectors </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">There are many reasons for this delay, but it is small compare to the long delay which occurs on throttle opening. The VAF/MAF sensors measure the increase in air well before the MAP sensor registers the change in manifold pressure. It takes time for the plenum to fill and change the pressure, that's why MAP systems need the throttle position to keep from going lean while the plenum is filling.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> what map sensor do the available map kits use. A gm or ford or something?
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">GM would probably be the most prevalent. Sunfire turbo cars used the 2-bar sensor and the 89 TA turbo used a 3-bar sensor.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> But the air that's measured at the entrance is not the same piece of air that's going into the engine, which has a different density (VE). </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Ve is not density, it is the ratio of actual ingested volume divided by theoretical volume which is directly related to pressure. The air measured is not the same piece actually entering the combustion chamber, but the particular piece doesn't matter it is the flow which is registered at the flow meter at the start of the intake tract that matters.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> you'll see there's a fraction of a second between when the manifold drops pressure from the closed throttle-plate on shifts and when the AFM/MAF sensor actually senses this and cuts the injectors </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">There are many reasons for this delay, but it is small compare to the long delay which occurs on throttle opening. The VAF/MAF sensors measure the increase in air well before the MAP sensor registers the change in manifold pressure. It takes time for the plenum to fill and change the pressure, that's why MAP systems need the throttle position to keep from going lean while the plenum is filling.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> what map sensor do the available map kits use. A gm or ford or something?
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">GM would probably be the most prevalent. Sunfire turbo cars used the 2-bar sensor and the 89 TA turbo used a 3-bar sensor.
03-10-2003, 12:43 AM
#12
Race Director
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Danno:
<strong>How can a MAF even sense VE? It's measuring only air at atmospheric density at the end of the pipe. I think you're talking about measuring the changes in volume of flow.
</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">It doesn't need to sense VE. It only needs to sense the air mass. Improve VE and your engine sucks in more air mass (all other things being equal).
The only thing that matters is air mass. MAP and other air flow sensors require more sensors to calculate air mass. An ECU (or DME in the case of a Porsche) can calculate air mass just from the voltage from the MAF. Easy peasy.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Danno:
<strong> After you stretch out the air-column the intake, it's a different volume and density. The air by that point has already been measured by a MAF.
</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">But the air mass doesn't change, so the volume and density don't matter.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Danno:
<strong>VE is not the same as total air mass. You can be sucking the same mass of air, yet be at a VE of .50 or .75.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">All other things being equal Danno, all other things being equal.
When all other things are equal, a change in VE will yield a change in air mass.
The point was that as you mod the engine with things that improve VE, a hot wire MAF doesn't need further calibrations (or really the ECU)unless you have improved VE sufficiently that the air mass being sucked in by the engine is beyond the MAF's calibration range.
<strong>How can a MAF even sense VE? It's measuring only air at atmospheric density at the end of the pipe. I think you're talking about measuring the changes in volume of flow.
</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">It doesn't need to sense VE. It only needs to sense the air mass. Improve VE and your engine sucks in more air mass (all other things being equal).
The only thing that matters is air mass. MAP and other air flow sensors require more sensors to calculate air mass. An ECU (or DME in the case of a Porsche) can calculate air mass just from the voltage from the MAF. Easy peasy.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Danno:
<strong> After you stretch out the air-column the intake, it's a different volume and density. The air by that point has already been measured by a MAF.
</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">But the air mass doesn't change, so the volume and density don't matter.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Danno:
<strong>VE is not the same as total air mass. You can be sucking the same mass of air, yet be at a VE of .50 or .75.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">All other things being equal Danno, all other things being equal.
When all other things are equal, a change in VE will yield a change in air mass.
The point was that as you mod the engine with things that improve VE, a hot wire MAF doesn't need further calibrations (or really the ECU)unless you have improved VE sufficiently that the air mass being sucked in by the engine is beyond the MAF's calibration range.
03-10-2003, 04:47 AM
#13
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"Ve is not density, it is the ratio of actual ingested volume divided by theoretical volume which is directly related to pressure."
I think we got the terms mixed up. The engine will always suck in 2.5L of volume per 4-stroke cycle, unless you've got rubber pistons or something. At a VE=0.50, there will be 1/2 the mass of air sucked in compared to theoretical. Assuming this is an NA motor, the pressure in the cylinder at BDC will be 1/2 of atmospheric for the same 2.5L volume. One-half of mass or 1/2 of pressure for the same volume means density is 1/2 as well. We can juggle terms and move things around in the VE equation, but volume must always be constant.
"But the air mass doesn't change, so the volume and density don't matter."
But total air-mass per volume does change and that's what we're interested in. For every 2.5L that's sucked in per 4-stroke cycle, how much mass is going into each combustion chamber? That will determine the pressure and density (volume will remain constant).
"Motronic updates RPM every 11.5 msec for the 944/951, if that is not real time enough I don't know what will be (~87 updates/sec). It updates the VAF reading anywhere from 25 to 50 times/sec (it's not a timed event like RPM)."
Yes, but it's really the air-flow time that I'm referring to. It doesn't matter how fast the computer is if it's given inaccurate data. The amount of time for the air that's measured to the time it takes to get into the engine causes a time-shift in the fuel-delivery curve. The fuel-flow doesn't exact match the air-flow.
"There are many reasons for this delay, but it is small compare to the long delay which occurs on throttle opening. The VAF/MAF sensors measure the increase in air well before the MAP sensor registers the change in manifold pressure. It takes time for the plenum to fill and change the pressure, that's why MAP systems need the throttle position to keep from going lean while the plenum is filling."
Again, that's exactly the mis-match I was talking about earlier with the throttle-closing example. Taking the inverse with the throttle-opening delays, why meter extra fuel when the extra air hasn't even entered the combustion chambers yet? This causes the extra puff of richness and soot you see when cars with AFM/MAF sensor accelerate. The sensor picks up extra air flow, but it's going to take 20-40 revolutions of the engine before this air fills the plenum and makes it into the engine. Meanwhile, the computer's been dumping in 5-10x more fuel than necessary. So in one instance, the computer is late in responding to air-flow changes and in the other, it's too early.
What I'm talking about here is not just pure sensor technology, but how it works with the EFI systems. Honda has always been at the forefront of these systems and their latest computers can adjust fuel & spark on an individual cylinder basis per revolution. They use separate maps for each cylinder to account for flow differences, and can measure air-fuel readings for each cylinder separately using a single O2-sensor. So I'm really getting down to the nitty-gritty of what does it take to accurately manage an engine at an infinitely small time-slice, not an overall average.
I think we got the terms mixed up. The engine will always suck in 2.5L of volume per 4-stroke cycle, unless you've got rubber pistons or something. At a VE=0.50, there will be 1/2 the mass of air sucked in compared to theoretical. Assuming this is an NA motor, the pressure in the cylinder at BDC will be 1/2 of atmospheric for the same 2.5L volume. One-half of mass or 1/2 of pressure for the same volume means density is 1/2 as well. We can juggle terms and move things around in the VE equation, but volume must always be constant.
"But the air mass doesn't change, so the volume and density don't matter."
But total air-mass per volume does change and that's what we're interested in. For every 2.5L that's sucked in per 4-stroke cycle, how much mass is going into each combustion chamber? That will determine the pressure and density (volume will remain constant).
"Motronic updates RPM every 11.5 msec for the 944/951, if that is not real time enough I don't know what will be (~87 updates/sec). It updates the VAF reading anywhere from 25 to 50 times/sec (it's not a timed event like RPM)."
Yes, but it's really the air-flow time that I'm referring to. It doesn't matter how fast the computer is if it's given inaccurate data. The amount of time for the air that's measured to the time it takes to get into the engine causes a time-shift in the fuel-delivery curve. The fuel-flow doesn't exact match the air-flow.
"There are many reasons for this delay, but it is small compare to the long delay which occurs on throttle opening. The VAF/MAF sensors measure the increase in air well before the MAP sensor registers the change in manifold pressure. It takes time for the plenum to fill and change the pressure, that's why MAP systems need the throttle position to keep from going lean while the plenum is filling."
Again, that's exactly the mis-match I was talking about earlier with the throttle-closing example. Taking the inverse with the throttle-opening delays, why meter extra fuel when the extra air hasn't even entered the combustion chambers yet? This causes the extra puff of richness and soot you see when cars with AFM/MAF sensor accelerate. The sensor picks up extra air flow, but it's going to take 20-40 revolutions of the engine before this air fills the plenum and makes it into the engine. Meanwhile, the computer's been dumping in 5-10x more fuel than necessary. So in one instance, the computer is late in responding to air-flow changes and in the other, it's too early.
What I'm talking about here is not just pure sensor technology, but how it works with the EFI systems. Honda has always been at the forefront of these systems and their latest computers can adjust fuel & spark on an individual cylinder basis per revolution. They use separate maps for each cylinder to account for flow differences, and can measure air-fuel readings for each cylinder separately using a single O2-sensor. So I'm really getting down to the nitty-gritty of what does it take to accurately manage an engine at an infinitely small time-slice, not an overall average.
03-10-2003, 02:57 PM
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</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> I think we got the terms mixed up. The engine will always suck in 2.5L of volume per 4-stroke cycle, unless you've got rubber pistons or something. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">It's not terms so much as pressure at the VAF/MAF and intake manifold being left out. The engine (as an air pump) wants to suck in 2.5L of air per cycle theoretically, but the position of the throttle plate is used to limit how much air actually is pumped by the engine. If 1 liter/cycle is measured by the VAF/MAF at atmospheric pressure, that 1 liter will be increased inside the intake manifold to 2.5 liters but at a lower pressure.
At idle a 944 consumes a little less than 300 l/min (STP at the VAF) at around 800 rpm. This is 400 cycles/min resulting in 300/400 l/cycle or .75 l/cycle. The resulting Ve would be .75/2.5 or .30. The manifold pressure should be close to .3 bar or -20 inHg.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> the inverse with the throttle-opening delays, why meter extra fuel when the extra air hasn't even entered the combustion chambers yet? </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">The VAF/MAF is not too early, the engine is consuming the air. The MAP sensor won't register this fact until the plenum is filled while the VAF/MAF register it immediately. Again the throttle position is necessary for the MAP system.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> This causes the extra puff of richness and soot you see when cars with AFM/MAF sensor accelerate. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">This is the acceleration enrichment programmed into Motronic. The 944/951 stock setup will increase the pulse width by as much as 250% if there is a large and quick increase in the VAF voltage. This is a momentary increase that decays quickly but the deed is done and you get the puffs.
Honda needs the kind of management systems they make for the redlines they have on their engines. 944/951 Motronic is already too busy counting teeth at redline and would not have time to do anything else above 7000 rpm.
As far as the individual cylinder AFR adjustments go, GM was doing this on the production Grand Am's back in 1996 using a single switching O2 sensor.
At idle a 944 consumes a little less than 300 l/min (STP at the VAF) at around 800 rpm. This is 400 cycles/min resulting in 300/400 l/cycle or .75 l/cycle. The resulting Ve would be .75/2.5 or .30. The manifold pressure should be close to .3 bar or -20 inHg.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> the inverse with the throttle-opening delays, why meter extra fuel when the extra air hasn't even entered the combustion chambers yet? </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">The VAF/MAF is not too early, the engine is consuming the air. The MAP sensor won't register this fact until the plenum is filled while the VAF/MAF register it immediately. Again the throttle position is necessary for the MAP system.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> This causes the extra puff of richness and soot you see when cars with AFM/MAF sensor accelerate. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">This is the acceleration enrichment programmed into Motronic. The 944/951 stock setup will increase the pulse width by as much as 250% if there is a large and quick increase in the VAF voltage. This is a momentary increase that decays quickly but the deed is done and you get the puffs.
Honda needs the kind of management systems they make for the redlines they have on their engines. 944/951 Motronic is already too busy counting teeth at redline and would not have time to do anything else above 7000 rpm.
As far as the individual cylinder AFR adjustments go, GM was doing this on the production Grand Am's back in 1996 using a single switching O2 sensor.
03-10-2003, 03:17 PM
#15
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> The VAF/MAF is not too early, the engine is consuming the air. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">How can that be???
Here's my real world experience - My MAF car with big turbo, big injectors and no cat shoots giant flames out the exhaust when upshifting when driving aggressively (ie. full throttle, letting off throttle quickly at 6500rpm+ to upshift). The instantaneous moment I let off the throttle, a huge volume of air is still being registered by my MAF sensor right after my air filter. However, my throttle body is firmly closed (air is compressible), and my injectors pump in tons of fuel for the small amount of air remaining in my intake manifold. Unburnt fuel ignites when it hits my red-hot turbine housing, and a flame shoots out my tail pipe.
Here's my real world experience - My MAF car with big turbo, big injectors and no cat shoots giant flames out the exhaust when upshifting when driving aggressively (ie. full throttle, letting off throttle quickly at 6500rpm+ to upshift). The instantaneous moment I let off the throttle, a huge volume of air is still being registered by my MAF sensor right after my air filter. However, my throttle body is firmly closed (air is compressible), and my injectors pump in tons of fuel for the small amount of air remaining in my intake manifold. Unburnt fuel ignites when it hits my red-hot turbine housing, and a flame shoots out my tail pipe.