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--- maffrequencylimits [2009/07/20 07:55]
twdorris
+++ maffrequencylimits [2024/03/15 11:16] (current)
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 Here is some basic information for the MAF sensors used in the DSM world.
-===== Mitsubishi MAFs =====
-Mitsubishi MAFs operate by measuring pressure, temperature and volume.  The ECU takes that data and multiplies it out to calculate air mass.  Air mass is then used to calculate fuel mass required to achieve a 14.7:1 A/F ratio.  That fuel mass is then used (along with the ECU's idea of which injectors are installed on the car) to calculate injector pulsewidth.  And then THAT is finally used to schedule the injector firing events.
-But it all starts with airflow measurement.  Like all devices, Mitsubishi MAFs were designed to operate in some pre-defined range of operating conditions.  One of those, of course, is the volume of air flowing through the MAF.  When the true volume exceeds the measuring capacity of a Mitsubishi MAF, you end up with an erratic volumetric output.  The erratic output feeds into the fuel calculation described above to produce an erratic A/F mixture.  And that produces erratic engine operation, typically while you're running wide open throttle!
+===== Mitsubishi MAF senors =====
-Mitsubishi MAFs report volumetric data using a frequency.  You can log this in ECMLink as MAFRaw.  You can monitor this frequency to determine how closely you're running to the known limits of that MAF.
+Mitsubishi MAF sensors operate by measuring pressure, temperature and volume.  The ECU takes that data and multiplies it out to calculate air mass.  Air mass is then used to calculate fuel mass required to achieve a 14.7:1 A/F ratio.  That fuel mass is then used (along with the ECU's idea of which injectors are installed on the car) to calculate injector pulsewidth.  And then THAT is finally used to schedule the injector firing events.
-==== 1G DSM MAF ====
+But it all starts with airflow measurement.  Like all devices, Mitsubishi MAF sensors were designed to operate in some pre-defined range of operating conditions.  One of those, of course, is the volume of air flowing through the MAF sensor.  When the true volume exceeds the measuring capacity of a Mitsubishi MAF sensor, you end up with an erratic volumetric output.  The erratic output feeds into the fuel calculation described above to produce an erratic A/F mixture.  And that produces erratic engine operation, typically while you're running wide open throttle!
-A stock, unhacked 1G DSM MAF will not accurately report frequencies above 2000hz.  That frequency represents roughly 180 lps (380 cfm) of volumetric airflow.  At standard temperature (around 77F) and sealevel pressure, that's about 210 gm/sec (28 lb/min) of mass airflow.
+Mitsubishi MAF sensors report volumetric data using a frequency.  You can log this in ECMLink as MAFRaw.  You can monitor this frequency to determine how closely you're running to the known limits of that MAF.
-==== 2G DSM MAF ====
-A stock, unhacked 2G DSM MAF (same as the 3000GT VR4 MAF) was designed to operate a bit higher.  You'd expect overflow on a 2G DSM MAF around 2700hz.  That frequency represents roughly 320 lps (about 680 cfm) of volumetric airflow.  At standard temperature (around 77F) and sealevel pressure, that's about 375 gm/sec (50 lb/min) of mass airflow.
+==== 1G DSM MAS ====
+A stock, unhacked 1G DSM MAS will not accurately report frequencies above 2000hz.  That frequency represents roughly 180 lps (380 cfm) of volumetric airflow.  At standard temperature (around 77F) and sealevel pressure, that's about 210 gm/sec (28 lb/min) of mass airflow.
-==== EVO8 MAF ====
-A stock, unhacked EVO8 MAF (effectively the same as the 3G Eclipse MAF) was designed to operate even higher!  You'd expect overflow on EVO8 MAF around 3000hz (we think...I'm not sure I've actually seen an EVO8 MAF overrun).  That frequency represents roughly 420 lps (about 890 cfm) of volumetric airflow.  At standard temperature (around 77F) and sealevel pressure, that's about 500 gm/sec (66 lb/min) of mass airflow.
+==== 2G DSM MAS ====
+A stock, unhacked 2G DSM MAS (same as the 3000GT VR4 MAS, same as an Lancer EVO1-3 MAS) was designed to operate a bit higher.  You'd expect overflow on a 2G DSM MAS around 2700hz.  That frequency represents roughly 320 lps (about 680 cfm) of volumetric airflow.  At standard temperature (around 77F) and sealevel pressure, that's about 375 gm/sec (50 lb/min) of mass airflow.
+==== EVO8 MAS ====
+A stock, unhacked EVO8 MAS (effectively the same as the 3G Eclipse MAS) was designed to operate even higher!  You'd expect overflow on EVO8 MAS around 3000hz (we think...I'm not sure I've actually seen an EVO8 MAS overrun).  That frequency represents roughly 420 lps (about 890 cfm) of volumetric airflow.  At standard temperature (around 77F) and sealevel pressure, that's about 500 gm/sec (66 lb/min) of mass airflow.
 ==== Summary ====
-^MAF         ^ Freq limit  ^ Volumetric limit   ^ Mass limit               ^
+^MAS         ^ Freq limit  ^ Volumetric limit   ^ Mass limit               ^
 |1G DSM      |       2000hz|180 lps (380 cfm)   |210 gm/sec (28 lb/min)    |
 |2G DSM      |       2700hz|320 lps (680 cfm)   |375 gm/sec (50 lb/min)    |
 |EVO8        |       3000hz|420 lps (890 cfm)   |500 gm/sec (66 lb/min)    |
-When running one of these MAFs anywhere near these limits, use ECMLink's MAF Clamp function.  Read the help files and forums for more information.  By using this function properly, you can effectively remove the upper airflow limitation of these MAF sensors.  Even so, it's highly recommended that the 1G DSM MAF not be used simply because its limit is too low to produce reliable MAF Clamp operation when running substantially more airflow than the sensor was designed to meter.
+When running one of these MAF sensors anywhere near these limits, use ECMLink's MAFClamp function.  Read the help files and forums for more information.  By using this function properly, you can effectively remove the upper airflow limitation of these MAF sensors.  Even so, it's highly recommended that the 1G DSM MAF not be used simply because its limit is too low to produce reliable MAFClamp operation when running substantially more airflow than the sensor was designed to meter.
-===== GM MAFs =====
+===== GM MAF sensors =====
-The two most common GM MAFs used on our DSMs are the 3" and 3.5" MAFs, part numbers 25180303 and 25179711, respectively.  These sensors operate fundamentally different than the Mitsubishi MAFs.  The GM MAFs work by measuring mass airflow directly.  They do not need temperature and baro data because they're not measuring volume.  They are reporting air mass directly as a frequency.
+The two most common GM MAF sensors used on our DSMs are the 3" and 3.5", part numbers 25180303 and 25179711, respectively.  These sensors operate fundamentally different than the Mitsubishi MAF sensors.  The GM MAF sensors work by measuring mass airflow directly.  They do not need temperature and baro data because they're not measuring volume.  They are reporting air mass directly as a frequency.
-The biggest problem, IMO, with these MAFs is that this frequency to mass mapping is non-linear.  So as airflow increases, it takes less and less change in frequency to present a larger and larger change in air mass.  This makes the system very sensitive to fluctuations in frequency output from the sensor.
+The biggest problem, IMO, with these MAF sensors is that this frequency to mass mapping is non-linear.  So as airflow increases, it takes less and less change in frequency to present a larger and larger change in air mass.  This makes the system very sensitive to fluctuations in frequency output from the sensor.
 Neither a MAF Translator nor the ECMLink V3 GM MAF cable allow you to see the raw GM MAF sensor frequency directly.  The MAF Translator provides a translation to stock DSM-like frequencies, while the ECMLink V3 GM MAF cable provides a simpler translation that produces raw frequencies that are quite different (but that the ECMLink V3 ECU code knows how to handle).  So it's best to avoid talking about limiting-frequencies when discussing a GM MAF sensor when used on a DSM and rather just talk about air-mass metering capability.

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