Over the years of production Mitsubishi has largely used a Karmen Vortex Mass Air Sensor (until lately but the only ones relevant to us are KV). These sensors are special from all others, I won't get into their exact working because it is quite complicated and moreover irrelevant to their employment in these cars but the important things to consider are these:
1) Airflow must go STRAIGHT through (hence the honeycomb screen)
2) Airflow must be UNIFORM across the the cross section of the flow pattern
3) They are NOT designed for blow through (PERIOD!)
4) They are NOT adjustable
5) They are NOT cleanable (contrary to popular belief)
Other things to know is that the MAF also contains the barometer and intake air temperature sensors in these applications.
A lot of people don't like our MAF's because they provide a large restriction on the intake. This may be true but not to the extent the world seems to believe and there are things one can do to make the most of using these sensors, upgrading them and tuning them for maximum performance. This is the prerequisite for a few points I'm going to make here.
3g's came with two different MAF's throughout their production. The first and by far most common is the 501 MAF sensor.
![Image]()
This sensor came on all GS's, RS's, and GT's over all years.
The other sensor is the 482.
![Image]()
This came on all GTS's, automatic and manual. It also came in some Montero Sports.
Notice the differences, 501 top, 482 bottom.
![Image]()
The 482 is geometrically identical to the 399 MAF that comes on the Evo. It however has different scalings. To my knowledge it has the same air metering capabilities, I have mine out close to 550 at the crank and I haven't topped it out yet. It provides a HUGE improvement in response and flow over the 501.
The 501 however is a different story. Of a few cars I've tuned and worked both suck through boosted and the big block naturally aspirated the 501 has failed to perform. It's as if it can't keep up with the air flow in these applications and had to be swapped out for the 482.
I've run into a number of tuning problems with both MAF's ultimately. Refer to the 5 key points I mentioned at the beginning of the post, unless all 5 are satisfied you will have to compensate in the tune for inaccuracy. The MAF's come attached directly to a straight flow air box providing for the flow requirements, the problem is when you upgrade to aftermarket intakes and upgrade engines a few things begin happening.
The first thing to note is that YOU CANNOT USE OILED AIR FILTERS WITH THESE MASS AIR SENSORS. The oil coats the filament and their metering abilities are eliminated. You can't clean these sensors either because the elements are coated with a special film that MAF cleaners dissolve.
Secondly, open filament air filters have a tendency to spin the air as it goes through the filter into an intake tube. The honey comb in the MAF helps take care of this, so that is not deletable.
The next problem, and most common results from installing just about any aftermarket intake. Here is a comparison between the MAF plate that comes in any AEM intake and a 4.5" plate that I bought off ebay.
![Image]()
The result with the AEM intake plate is it focuses air into the center of the MAF. This can skew the density distribution of air through the cross section of flow through the MAF. This doesn't hurt things in stock form because the charge velocities on a stock engine or other low horsepower application aren't high enough work against an even air distribution.
However when bigger engines or forced induction begin pulling in more air the velocities through the MAF start climbing into a range where the elasticity of air causes the distribution to start changing. A small plate like the one that comes with the AEM (or ANY ebay intake) will ruin the meterability of the 482 because the opening is larger than the plate diameter. As I said earlier I have no idea why the 501 loses its functionality, but I have yet to be able to make one work well on anything more potent then a bolted on 3 liter, they all run lean to the point that it can't be compensated for.
On the 482 plates like these cause flat spots in the MAF curve, meaning chunks of your rpm range always run lean or rich. The fix I've found for these is the 4 or 4.5" plate.
![Image]()
This is one of the reasons I will always recommend a custom intake. Put a filter right on the MAF with the 4.5" plate and a 3" pipe. What it makes for is an even air density across the maf and straight flow. As well as the least restriction you can get for the meterability. Like I said, I'm making something like 550 crank right now with the 482 and I'm using 100% stock MAF curves and settings.
On the 501.
![Image]()
On the 482
![Image]()
Swapping these MAF's REQUIRES a flash. There are 4 tables related to air metering with the maf. MAF Size, MAF Sensor Filtering, MAF Smoothing and MAF Scaling.
If you're going to be doing a MAF swap and doing any level of tuning you'll want to follow this tutorial for redefining your Scaling and Smoothing tables.
How-To: Rescale your MAF (without pics) - evolutionm.net
What this does is put the left column of your tables into HZ. This is the loggable readout given to the ECU by AirFlowHz in Evoscan. To tune the MAF you want to log your wideband, airflowhz, AFRmap, rpm and ecuload to see what your target AFR's are, when and how far off they are. Given properly dialed in injectors this method can be used to track down a MAF curve. If you have the appropriate intake however this should be unnecessary.
The tables I'm posting below are for a ROM CONVERTED BY THE ABOVE TUTORIAL.
For the 482:
Size: 358.8
Sensor Filtering:
192
241
Smoothing:
141
140
134
132
131
131
131
131
131
132
132
132
132
132
133
132
131
130
130
130
130
Scaling:
145
150
164
176
181
184
188
192
196
198
202
204
207
213
218
223
231
235
235
233
230
Since no one would possibly upgrade to the 501 I won't bother posting the settings for it. The 399 MAF is also swappable but I don't have the scalings for that on hand at the moment. If someone finds them feel free to post.
1) Airflow must go STRAIGHT through (hence the honeycomb screen)
2) Airflow must be UNIFORM across the the cross section of the flow pattern
3) They are NOT designed for blow through (PERIOD!)
4) They are NOT adjustable
5) They are NOT cleanable (contrary to popular belief)
Other things to know is that the MAF also contains the barometer and intake air temperature sensors in these applications.
A lot of people don't like our MAF's because they provide a large restriction on the intake. This may be true but not to the extent the world seems to believe and there are things one can do to make the most of using these sensors, upgrading them and tuning them for maximum performance. This is the prerequisite for a few points I'm going to make here.
3g's came with two different MAF's throughout their production. The first and by far most common is the 501 MAF sensor.
This sensor came on all GS's, RS's, and GT's over all years.
The other sensor is the 482.
This came on all GTS's, automatic and manual. It also came in some Montero Sports.
Notice the differences, 501 top, 482 bottom.
The 482 is geometrically identical to the 399 MAF that comes on the Evo. It however has different scalings. To my knowledge it has the same air metering capabilities, I have mine out close to 550 at the crank and I haven't topped it out yet. It provides a HUGE improvement in response and flow over the 501.
The 501 however is a different story. Of a few cars I've tuned and worked both suck through boosted and the big block naturally aspirated the 501 has failed to perform. It's as if it can't keep up with the air flow in these applications and had to be swapped out for the 482.
I've run into a number of tuning problems with both MAF's ultimately. Refer to the 5 key points I mentioned at the beginning of the post, unless all 5 are satisfied you will have to compensate in the tune for inaccuracy. The MAF's come attached directly to a straight flow air box providing for the flow requirements, the problem is when you upgrade to aftermarket intakes and upgrade engines a few things begin happening.
The first thing to note is that YOU CANNOT USE OILED AIR FILTERS WITH THESE MASS AIR SENSORS. The oil coats the filament and their metering abilities are eliminated. You can't clean these sensors either because the elements are coated with a special film that MAF cleaners dissolve.
Secondly, open filament air filters have a tendency to spin the air as it goes through the filter into an intake tube. The honey comb in the MAF helps take care of this, so that is not deletable.
The next problem, and most common results from installing just about any aftermarket intake. Here is a comparison between the MAF plate that comes in any AEM intake and a 4.5" plate that I bought off ebay.
The result with the AEM intake plate is it focuses air into the center of the MAF. This can skew the density distribution of air through the cross section of flow through the MAF. This doesn't hurt things in stock form because the charge velocities on a stock engine or other low horsepower application aren't high enough work against an even air distribution.
However when bigger engines or forced induction begin pulling in more air the velocities through the MAF start climbing into a range where the elasticity of air causes the distribution to start changing. A small plate like the one that comes with the AEM (or ANY ebay intake) will ruin the meterability of the 482 because the opening is larger than the plate diameter. As I said earlier I have no idea why the 501 loses its functionality, but I have yet to be able to make one work well on anything more potent then a bolted on 3 liter, they all run lean to the point that it can't be compensated for.
On the 482 plates like these cause flat spots in the MAF curve, meaning chunks of your rpm range always run lean or rich. The fix I've found for these is the 4 or 4.5" plate.
This is one of the reasons I will always recommend a custom intake. Put a filter right on the MAF with the 4.5" plate and a 3" pipe. What it makes for is an even air density across the maf and straight flow. As well as the least restriction you can get for the meterability. Like I said, I'm making something like 550 crank right now with the 482 and I'm using 100% stock MAF curves and settings.
On the 501.
On the 482
Swapping these MAF's REQUIRES a flash. There are 4 tables related to air metering with the maf. MAF Size, MAF Sensor Filtering, MAF Smoothing and MAF Scaling.
If you're going to be doing a MAF swap and doing any level of tuning you'll want to follow this tutorial for redefining your Scaling and Smoothing tables.
How-To: Rescale your MAF (without pics) - evolutionm.net
What this does is put the left column of your tables into HZ. This is the loggable readout given to the ECU by AirFlowHz in Evoscan. To tune the MAF you want to log your wideband, airflowhz, AFRmap, rpm and ecuload to see what your target AFR's are, when and how far off they are. Given properly dialed in injectors this method can be used to track down a MAF curve. If you have the appropriate intake however this should be unnecessary.
The tables I'm posting below are for a ROM CONVERTED BY THE ABOVE TUTORIAL.
For the 482:
Size: 358.8
Sensor Filtering:
192
241
Smoothing:
141
140
134
132
131
131
131
131
131
132
132
132
132
132
133
132
131
130
130
130
130
Scaling:
145
150
164
176
181
184
188
192
196
198
202
204
207
213
218
223
231
235
235
233
230
Since no one would possibly upgrade to the 501 I won't bother posting the settings for it. The 399 MAF is also swappable but I don't have the scalings for that on hand at the moment. If someone finds them feel free to post.
