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How to Scale your MAF for Flash Tuning (Cobb, Hymee)

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How to Scale your MAF for Flash Tuning (Cobb, Hymee)

Old 04-08-2009, 04:03 PM
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Even worse for me because I discovered that i only have one fuel map that covers all 6 gears so i have to richen it up over a wide band to keep it going too lean ....
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Old 04-08-2009, 06:44 PM
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Ideally you should scale the MAF with the stock injectors with stock injector scaling. Once the MAF is scaled, then go install and scale the injectors. Both scalings affect fuel trims making it very hard to tune both variables at once. I have never tuned an RX8 but carbon asked my opinion since I do tune Mitsus and Subies. When I tune a MAF I log fuel trims and airflow under closed loop fueling. Ideally fuel trims should be close to zero (in reality zero is impossible but anything under 3-4% is good). Bear in mind that STFT will get pushed into LTFT. So the STFT requires the most attention. In Evo tuning we use airflow under cruise closed loop conditions and at idle to figure out the % correction. eg, if at an idle of 50 hz airflow, my STFT is consistently +10%, then the ECU is adding 10% additional fuel to account for 10% excessive airflow. So the MAF scaling needs to be decreased 10% at that airflow range. You do the same for different cruise conditions/airflow ranges. Once the MAF is scaled, you repeat the same for injectors. Although a lot of injector latency numbers are already published and can just be copied.

Last edited by shadow1; 04-09-2009 at 07:55 AM.
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Old 04-08-2009, 08:32 PM
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wouldnt it just be easier to log afr target and afr actual along with maf voltage and compute your adjustments from there?
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Old 04-08-2009, 08:56 PM
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Originally Posted by lurch519 View Post
wouldnt it just be easier to log afr target and afr actual along with maf voltage and compute your adjustments from there?
Uh, that is exactly what I said. Problem is, if you search for details on this process, the are in error or not detailed.

Originally Posted by shadow1 View Post
Ideally you should scale the MAF with the stock injectors with stock injector scaling. Once the MAF is scaled, then installed and scale the injectors. Both scalings affect fuel trims making it very hard to tune both variables at once. I have never tuned an RX8 but carbon asked my opinion since I do tune Mitsus and Subies. When I tune a MAF I log fuel trims and airflow under closed loop fueling. Ideally fuel trims should be close to zero (in reality zero is impossible but anything under 3-4% is good). Bear in mind that STFT will get pushed into LTFT. So the STFT requires the most attention. In Evo tuning we use airflow under cruise closed loop conditions and at idle to figure out the % correction. eg, if at an idle of 50 hz airflow, my STFT is consistently +10%, then the ECU is adding 10% additional fuel to account for 10% excessive airflow. So the MAF scaling needs to be decreased 10% at that airflow range. You do the same for different cruise conditions/airflow ranges. Once the MAF is scaled, you repeat the same for injectors. Although a lot of injector latency numbers are already published and can just be copied.

Thanks. Scaling with the stock injectors is not possible as I was not aware at the time I installed them that I would have to do this. And, as you well know, I am not taking them off. In any case, the flow numbers on the stockers are as much a shot in the dark as the upgrades, and the scaling (if necessary) can happen after the MAF is nailed down.

I dont know anything about the evo, (and only infinitesimally more about the RX8,) but as for scaling MAF cali in closed loop on the RX8, it seems that would miss all the RPM ranges above about 4000rpm, below which is barely usable low load territory. Scaling above this is the entire range where you can go "pop!" What you learn below 4000rpm cant be used to scale above this rpm.

I now understand what you were talking about over sushi, but I am nearly certain that the methods are not transferable between the cars.
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Old 04-08-2009, 09:07 PM
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my take on what you posted, is that you log afr actual, maf voltage, load, etc and lookup in the expected afr table in the map. what i was suggesting is to log both afr actual and afr expected at the same time, as well as maf voltage, then just computing from there.
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Old 04-08-2009, 09:21 PM
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OH! I didn't understand you. I dont have the capability to log expected AFR. That would make this process MUCH easier. It is possible that those that can do live datalogging with the dongle and a computer can do this. Even if this is possible, I, unfortunately, can not get my computer hooked up to talk to the car. I have basically given up and just log with the AP. But, yeah, logging expected AFR would be a nice thing to have for this process.
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Old 04-08-2009, 10:11 PM
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Originally Posted by carbonRX8 View Post
OH! I didn't understand you. I dont have the capability to log expected AFR. That would make this process MUCH easier. It is possible that those that can do live datalogging with the dongle and a computer can do this. Even if this is possible, I, unfortunately, can not get my computer hooked up to talk to the car. I have basically given up and just log with the AP. But, yeah, logging expected AFR would be a nice thing to have for this process.
Yeah that is my way of doing it - but you have to set your fuel maps up for it prior to - with your excel file though you can just use the AFR/lambda from your fuel base map.

I am def down to have this in my thread - can a mod move it?
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Old 04-08-2009, 10:27 PM
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Originally Posted by Kane View Post
I am def down to have this in my thread - can a mod move it?
Seconded.
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Old 04-08-2009, 10:31 PM
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Is it in the wrong forum?
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Old 04-08-2009, 10:43 PM
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Combine them - mine and Carbons?
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Old 04-08-2009, 11:15 PM
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Originally Posted by lurch519 View Post
my take on what you posted, is that you log afr actual, maf voltage, load, etc and lookup in the expected afr table in the map. what i was suggesting is to log both afr actual and afr expected at the same time, as well as maf voltage, then just computing from there.
That would be sweet.....if you could do it. The AP can't log Target Lambda tho.
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Old 04-08-2009, 11:57 PM
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Originally Posted by chickenwafer View Post
That would be sweet.....if you could do it. The AP can't log Target Lambda tho.
Set them to 1 like I told you on the phone for low load areas - and you got your target.
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Old 04-09-2009, 07:18 AM
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AH! So I understand a little more now what you were trying to do, Kane. Your step one is fine, mathematically, but your suggestion to scale the entire maf curve by what ever you see at lower load/flow is not useful. WHat happens at low flow does not predict high. Furthermore, your step two needs, as you say, more math; specifically to convert to using the % error equation to determine the adjustment factor.

Download those excel addons and try them out. I can send you my excel sheet that has a way to convert a matrix of fueling to indexed fueling and the set up to extract expected AFR. Using this, you can see that you could completely automate MAF calibration. Even to the point where you take an excel macro, feed it your fuel table, current MAF cali, and a datalog, and it spits out a new, spline-fit, MAF calibration. Lotta work tho.
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Old 04-09-2009, 08:11 AM
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Originally Posted by carbonRX8 View Post
Thanks. Scaling with the stock injectors is not possible as I was not aware at the time I installed them that I would have to do this. And, as you well know, I am not taking them off. In any case, the flow numbers on the stockers are as much a shot in the dark as the upgrades, and the scaling (if necessary) can happen after the MAF is nailed down.

I dont know anything about the evo, (and only infinitesimally more about the RX8,) but as for scaling MAF cali in closed loop on the RX8, it seems that would miss all the RPM ranges above about 4000rpm, below which is barely usable low load territory. Scaling above this is the entire range where you can go "pop!" What you learn below 4000rpm cant be used to scale above this rpm.

I now understand what you were talking about over sushi, but I am nearly certain that the methods are not transferable between the cars.
I don't bother scaling for high load and/or high rpm ranges. At those ranges, the ECU is in open loop fueling and I can tune for what I need via the OL fuel map. In Evo tuning, you need to adjust MAF scaling to fix closed loop fueling issues for fuel economy and to prevent lean/rich CELs and for a good idle. These conditions only occur off boost when the ECU is striving for stoichiometric fueling (14.7:1).

Since you are scaling the MAF based on lambda and airflow, I personally don't see how you can properly scale the MAF when you are going to be running rich across the board with bigger non-stock injectors. Also I would assume that the RX8 has a fuel injector scaling table and injector voltage latency table. Or at least I would hope that the Cobb Accessport has those functions. At the very least, get the published latency numbers for the injectors and use a rough approximation of the scaling (roughly 85% of the published flow). Then you will at least be in the ball park for injector scaling. What are the stock injector sizes and what are your aftermarket injector sizes?

Last edited by shadow1; 04-09-2009 at 08:14 AM.
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Old 04-09-2009, 09:37 AM
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Originally Posted by shadow1 View Post
I don't bother scaling for high load and/or high rpm ranges. At those ranges, the ECU is in open loop fueling and I can tune for what I need via the OL fuel map. In Evo tuning, you need to adjust MAF scaling to fix closed loop fueling issues for fuel economy and to prevent lean/rich CELs and for a good idle. These conditions only occur off boost when the ECU is striving for stoichiometric fueling (14.7:1).
So, specific to tuning with the accessport, and perhaps specific to the RX8 pcm, the OL maps are afr targets that the pcm wants to hit. The computer doesnt read from the wb02 but it does use the maf to determine how much fuel is required. If the maf is miscalibrated, the fuel is wrong. So duty cycles are determined by the computer, not directly from a map. The maf is critical in that respect. Also, just fyi, the maps are load-based, not pressure-based. After you get used to that, it actually makes a lot of sense.

Originally Posted by shadow1 View Post
Since you are scaling the MAF based on lambda and airflow, I personally don't see how you can properly scale the MAF when you are going to be running rich across the board with bigger non-stock injectors. Also I would assume that the RX8 has a fuel injector scaling table and injector voltage latency table. Or at least I would hope that the Cobb Accessport has those functions. At the very least, get the published latency numbers for the injectors and use a rough approximation of the scaling (roughly 85% of the published flow). Then you will at least be in the ball park for injector scaling. What are the stock injector sizes and what are your aftermarket injector sizes?
There is a separate individual scaling factor that can be used as a first approximation for injector size. I have left the latencies alone until I can get more information on my specific injectors. Unfortunately, I only know the identity of my 780cc/min injectors. My 650s had no identifing marks.
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Old 04-09-2009, 10:41 AM
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Originally Posted by carbonRX8 View Post
So, specific to tuning with the accessport, and perhaps specific to the RX8 pcm, the OL maps are afr targets that the pcm wants to hit. The computer doesnt read from the wb02 but it does use the maf to determine how much fuel is required. If the maf is miscalibrated, the fuel is wrong. So duty cycles are determined by the computer, not directly from a map. The maf is critical in that respect. Also, just fyi, the maps are load-based, not pressure-based. After you get used to that, it actually makes a lot of sense.
There is more to it then that though. The amount of fuel the pcm delivers in open loop is also corrected based on the VE tables, load limiting tables, and more... its not just the maf being off
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Old 04-09-2009, 11:00 AM
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Originally Posted by r0tor View Post
There is more to it then that though. The amount of fuel the pcm delivers in open loop is also corrected based on the VE tables, load limiting tables, and more... its not just the maf being off
Noted. Although relevant to this discussion (with a misguided piston driven tuner) I think it is sufficent to describe it in the simplest terms. Measured airflow drives fueling in OL. How that signal is modulated after the airflow is measured is an important, but secondary, consideration.
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Old 04-09-2009, 11:09 AM
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Originally Posted by carbonRX8 View Post
So, specific to tuning with the accessport, and perhaps specific to the RX8 pcm, the OL maps are afr targets that the pcm wants to hit. The computer doesnt read from the wb02 but it does use the maf to determine how much fuel is required. If the maf is miscalibrated, the fuel is wrong. So duty cycles are determined by the computer, not directly from a map. The maf is critical in that respect. Also, just fyi, the maps are load-based, not pressure-based. After you get used to that, it actually makes a lot of sense.

There is a separate individual scaling factor that can be used as a first approximation for injector size. I have left the latencies alone until I can get more information on my specific injectors. Unfortunately, I only know the identity of my 780cc/min injectors. My 650s had no identifing marks.
Your 1st statement implies the the RX8 has a wideband O2 sensor from the factory. I agree, if the ECU is shooting for an AFR target than yes, the MAF needs to scaled at all rpm/load ranges. In addition, that technically means that you are no longer open loop... The ECU is using O2 sensor feedback to hit a goal lambda for a particular rpm and load. If that is the case, then tuning is simple. Plug in your goal lambda under boost and let the ECU figure the rest.

There are really only 3 brands of injectors regardless of who sells or labels them:
1. JDM injectors are made by Denso and sold under Greddy, Blitz, HKS, OEM labels.
2. USDM injectors are made by Delphi and sold under PTE, Fuel injector clinic, RC engineering, and tons of other labels (BTW I use these in my Evo).
3. German injectors made by Siemens.

Latency numbers are locatable via google. You just need to know which 650cc injector you have for example (Denso or Delphi). Also different sellers rate their injectors differently. Fuel Injector clinic rates their injectors conservatively. What they call a 750cc injector, PTE sells as a 780cc injector. But they are the same injector. There is a LOT of latency numbers available on the evo forums.
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Old 04-09-2009, 11:16 AM
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One more point: In Evo tuning, our open loop fuel maps have "AFR" numbers in them for particular loads and rpms. These are not true AFRs in a modded Evo. Once you mod, the numbers are meaningless. You have to make adjustments to these numbers to achieve the wideband AFRs numbers that you want. eg, if my AFR at 4000 rpm and 250% load is 10.5:1 I would increase the numbers in those cells by 2% to get my WB AFR above 11:1. The actual number in the map is meaningless (it could say "9.9"). What is important is what change I make to the number. I say all this because I wonder if open loop fueling in RX8's is similar.
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Old 04-09-2009, 11:27 AM
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Originally Posted by shadow1 View Post
Your 1st statement implies the the RX8 has a wideband O2 sensor from the factory. I agree, if the ECU is shooting for an AFR target than yes, the MAF needs to scaled at all rpm/load ranges. In addition, that technically means that you are no longer open loop... The ECU is using O2 sensor feedback to hit a goal lambda for a particular rpm and load. If that is the case, then tuning is simple. Plug in your goal lambda under boost and let the ECU figure the rest.
Yes, there is a wbo2 on the car from the factory. In CL the pcm uses this information to hit targets. Under high load, I do not believe that the wb02 is used, hence, OL. What specific algorithms that are used to determine fuel is complicated as rotor noted, but the general idea is that, yes, put in your target afr and hit the gas.


Originally Posted by shadow1 View Post
There are really only 3 brands of injectors regardless of who sells or labels them:
1. JDM injectors are made by Denso and sold under Greddy, Blitz, HKS, OEM labels.
2. USDM injectors are made by Delphi and sold under PTE, Fuel injector clinic, RC engineering, and tons of other labels (BTW I use these in my Evo).
3. German injectors made by Siemens.

Latency numbers are locatable via google. You just need to know which 650cc injector you have for example (Denso or Delphi). Also different sellers rate their injectors differently. Fuel Injector clinic rates their injectors conservatively. What they call a 750cc injector, PTE sells as a 780cc injector. But they are the same injector. There is a LOT of latency numbers available on the evo forums.
I will post a pic of the 650s to help get an idea of what they are.
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Old 04-09-2009, 11:32 AM
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Originally Posted by shadow1 View Post
One more point: In Evo tuning, our open loop fuel maps have "AFR" numbers in them for particular loads and rpms. These are not true AFRs in a modded Evo. Once you mod, the numbers are meaningless. You have to make adjustments to these numbers to achieve the wideband AFRs numbers that you want. eg, if my AFR at 4000 rpm and 250% load is 10.5:1 I would increase the numbers in those cells by 2% to get my WB AFR above 11:1. The actual number in the map is meaningless (it could say "9.9"). What is important is what change I make to the number. I say all this because I wonder if open loop fueling in RX8's is similar.
It is similar, but how I understand the OL fueling to work in the RX8, if the maf is scaled correctly and the injectors are scaled correctly, and no adjustments are made by the pcm by a multitude of other tables, the lambda you put in should be the lambda you get out. Again this is much further down the line in actual tuning than what I was discussing for maf calibration.
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Old 04-09-2009, 11:40 AM
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Originally Posted by carbonRX8 View Post
It is similar, but how I understand the OL fueling to work in the RX8, if the maf is scaled correctly and the injectors are scaled correctly, and no adjustments are made by the pcm by a multitude of other tables, the lambda you put in should be the lambda you get out. Again this is much further down the line in actual tuning than what I was discussing for maf calibration.
I would only agree with this statement if you are running n/a with stock injectors and stock exhaust, etc. With boost and all your other mods, the VE of the motor is radically different. I believe that the Evo method of tuning would work fine since your "target" lambda under OL fueling is now meaningless with forced induction. If I am correct then you guys can skip high load/rpm MAF scaling headaches. Just compensate in your OL fuel maps.

Last edited by shadow1; 04-09-2009 at 11:42 AM.
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Old 04-09-2009, 02:17 PM
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Originally Posted by carbonRX8 View Post
AH! So I understand a little more now what you were trying to do, Kane. Your step one is fine, mathematically, but your suggestion to scale the entire maf curve by what ever you see at lower load/flow is not useful. WHat happens at low flow does not predict high. Furthermore, your step two needs, as you say, more math; specifically to convert to using the % error equation to determine the adjustment factor.

Download those excel addons and try them out. I can send you my excel sheet that has a way to convert a matrix of fueling to indexed fueling and the set up to extract expected AFR. Using this, you can see that you could completely automate MAF calibration. Even to the point where you take an excel macro, feed it your fuel table, current MAF cali, and a datalog, and it spits out a new, spline-fit, MAF calibration. Lotta work tho.
I'll look at it this weekend and update the first post. But to clarify - YOU ONLY correct the MAF at high loads and high RPM's if you are trending by a certain %. All that does is bring your higher MAF voltages closer to actual to be safer UNTIL you actually load up the car and scale them. This is critical in FI because if your whole MAF needs to be scaled by say 10% - and you don't scale the higher points as well then your going to be dangerously lean when you access those points in the MAF.


Originally Posted by carbonRX8 View Post
Yes, there is a wbo2 on the car from the factory. In CL the pcm uses this information to hit targets. Under high load, I do not believe that the wb02 is used, hence, OL. What specific algorithms that are used to determine fuel is complicated as rotor noted, but the general idea is that, yes, put in your target afr and hit the gas.


I will post a pic of the 650s to help get an idea of what they are.
Correct - the WBO2 does not provide fuel corrections in OL - but the g/sec calculation determines absolute load, which determines fuel. ACCURACY is KEY - get your sensors and tables right - then tune.

Originally Posted by shadow1 View Post
I would only agree with this statement if you are running n/a with stock injectors and stock exhaust, etc. With boost and all your other mods, the VE of the motor is radically different. I believe that the Evo method of tuning would work fine since your "target" lambda under OL fueling is now meaningless with forced induction. If I am correct then you guys can skip high load/rpm MAF scaling headaches. Just compensate in your OL fuel maps.
It is not meaningless - you want accurate sensor information first - then set your fuel maps tp the desired Lambda. We don't need to trick stuff any more with a flash tuner - so don't. Take the time and do it right.
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Old 04-09-2009, 03:48 PM
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You will never get the open loop AFR to match the targets in the table. To do that you need to get all 3 injectors perfect, you need to get the maf perfect, the engine VE perfect, the fuel VE table perfect, and then deal with the flow disturbances caused by the various ports opening and closing.

You are not going to get all that perfect unless you spend wwaaaayyyy too long on an chassis dyno holding the car in a steady state condition in all areas of the maps.
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Old 04-09-2009, 04:57 PM
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Originally Posted by r0tor View Post
You will never get the open loop AFR to match the targets in the table. To do that you need to get all 3 injectors perfect, you need to get the maf perfect, the engine VE perfect, the fuel VE table perfect, and then deal with the flow disturbances caused by the various ports opening and closing.

You are not going to get all that perfect unless you spend wwaaaayyyy too long on an chassis dyno holding the car in a steady state condition in all areas of the maps.
I agree . I spent all of yesterday trying to get my maf lined up with my lambda in the fuel tables . It did not work . I got things near perfect at higher flow rates IE actual lambda lining up with expected lambda at 150-170% load . But found that at 110-130% load I was way too rich .
I could not make sense of it but that was the reality .
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