Best way to tune MAF

[murfie]

I think tuning a digital MAF transfer is not the same as tuning an analog MAF transfer.

Analog MAF sensors used 0-5v to control the temperature of a wire. I was pretty simple more air mass means cooler wire means more voltage. Modification to the air flow usually equaled more air mass/density and therefore required more voltage. The problem was you are limited to the maximum voltage to keep the hot wire temperature constant. This meant there was a air flow above a certain point that the sensor could not heat the wire enough to properly calculate. At that point you could toss out the MAF and go full speed density or buy a MAF that was beefier and could handle more air flow.

Digital MAF sensors use only two voltages, on voltage and off voltage. This means it controls the temperature of the wire by frequency. Higher frequency mean more heat and more air flow. This also means much much higher upper limit to air flow calculations with more accurate resolution as frequency can go from very low to as fast as the circuit physically allows which is really fast. The table in the editor is period vs air mass. period is the reciprocal of frequency meaning period = 1/frequency so frequency = 1/ period. This is why higher frequency is smaller period. you can also see that frequency or period can never be 0, but be in theory infinite.

If the MAF is in the stock housing and it reads 500 period that means x air flow. If you take that same air mass and pass it through a larger housing it will be less dense. less density means less cooling effect on the hot wire. This means periods for the same air mass should be higher. If you say 500 period = 1.5x air flow in a bigger pipe you are accomplishing this. you could also say x air flow = 750 period and still accomplish the same result. In a larger tube the MAF will require less frequency to maintain hot wire temperature. This would mean it would operate at relatively higher periods in a larger housing. When the ratio is applied to the air flow it expands the resolution or the air flow which is not necessary. If we apply the correction values to the period instead of the air flow it should shift the resolution of the period in a more accurate position for aftermarket modifications.

attachment to shows period modification(1.38) vs air flow modification(1.38) vs stock. Notice how the resolution of the air flow in commonly used areas(1lb/min-55lb/min) is affected.

CurveMAF.PNG

[rhinogt]

So are you saying it would be better to apply changes in the MAF to the axis of the MAF period table instead of the values?

[murfie]

Yes the digital sensor doesn't need more flow resolution by sacrificing low flow resolution. You can just modify the period and maintain flow resolution for accuracy if not improve its resolution.

[rhinogt]

I will have to give that a try tomorrow.

[Higgs Boson]

you can edit the axis to maximize resolution if you want, but the changes to the hardware create airflow changes so correct the airflow. if you left your car stock and somehow modified applied voltage to the maf then you could edit the period axis to correct back to the right airflow. again, you edit what you changed. keep it simple.

the maf period axis goes down to 0 at the top cell, if you run out of space at wot, you can just put a 0 in that cell and interpolate down to wherever your wot airflow starts when you floor it at low RPM, mine is right at 166. my car idles at .8 lb/min at 621us. you could probably just rescale the maf axis from 700 at the bottom to 0 at the top to maximize resolution, if you need it up top. otherwise you can scale from 700 up to your max maf cell at wot, maybe 110 or so.

in reality, this isn't even necessary, airflow changes are so slow at wot you don't need more resolution there. maybe you would want more if we had big cams with reversion so bad they mess up low flow maf readings....been there done that. and that's the only time I ever felt like I was better off going to SD.

[murfie]

you gave me the idea to look at period when you said you didn't apply a base correction. Seeing as you are having the easiest time tuning the torque tables I think its because you didn't sacrifice your low air flow resolution. You just applied the error to the current resolution. Period does not increase voltage to the MAF. It works like an AC circuit and increases frequency. If you used a volt meter on it you would see a constant voltage no matter the air flowing through the meter. When I did the calculation the Hertz in the editor goes over 20k.

1/0.000166s = 6000+ hertz.

1/0.000621=1600+ hertz.

hertz is how many times it goes back and forth between 0 v and maximum volts ( I think its 5). It works like duty cycles.

I think if you know air flow will be between 0 and 50lb/min you want the ECU to have the most resolution between those points. Period can be anywhere from 0(infinity lb/min) to infinity(0lb/min) why not change those numbers since they are going to be more accurate. You modified airflow but that directly effects period which we can log directly from the MAF sensor output. you don't have to apply a base correction to period but applying error to period will give more accurate results than modifying airflow values based on inaccurate sensor readings.

My car stock idles at .85lb/min and 460us. makes sense that yours is higher as air is more available and moving slower. 4rd gear at 35 MPH WOT 2275 rpm it goes to 160us and 12 lb/min (I would have guessed yours to be a bit higher maybe your lb/min is greater). By 4k its down to 125us and 26lb/min. In 3rd 20MPH 1200rpm spikes to 2200 rpm the converter is unlocked and I get a spike up to 14lb/min at 170us. during this time STFT are 0. once it settles its at about 165us and 11.5 lb/min. By 4k its about 125us with 24lb/min. By 5500 its at 110us with 35lb/min. all with 75* iat. period bounces up and down as MAF climbs. neutral rev at 4k it goes to 125us and 23lb/min. Shows you load effects air velocity by slowing it down. If your MAF curve if off your load calculations will be off and the ECU will think the air is moving faster or slower than it really is giving you the wrong ignition, IMRC, cam events, ect. In the same respect if you alter any of these values when the MAF is calibrated right it should give you the benefit of the tune modification as long as the speed density cross check doesn't say its off. That's where the multipliers come in.

[murfie]

So yes trying to adjust the period is only use full in extremely fine adjustments. Probably fruitless for the effort and unnecessary.

What I found was ratioing your maf housing got long term fuel trims very close. With some adjustments it was all under 2% average. After that I looked at maximum and minimum and applied the difference. Mine was 4% and -2% so I multiplied the curve by .98. This got my ltft with in .7 every where. Max was .73 and min was 0. I'm pretty happy with my results.

I left the top and bottom cells as they were and only changed the middle cells. It took an hour total and three flashes.

[txcharlie]

I think tuning a digital MAF transfer is not the same as tuning an analog MAF transfer.

Analog MAF sensors used 0-5v to control the temperature of a wire. I was pretty simple more air mass means cooler wire means more voltage. Modification to the air flow usually equaled more air mass/density and therefore required more voltage. The problem was you are limited to the maximum voltage to keep the hot wire temperature constant. This meant there was a air flow above a certain point that the sensor could not heat the wire enough to properly calculate. At that point you could toss out the MAF and go full speed density or buy a MAF that was beefier and could handle more air flow.

Digital MAF sensors use only two voltages, on voltage and off voltage. This means it controls the temperature of the wire by frequency. Higher frequency mean more heat and more air flow. This also means much much higher upper limit to air flow calculations with more accurate resolution as frequency can go from very low to as fast as the circuit physically allows which is really fast. The table in the editor is period vs air mass. period is the reciprocal of frequency meaning period = 1/frequency so frequency = 1/ period. This is why higher frequency is smaller period. you can also see that frequency or period can never be 0, but be in theory infinite.

If the MAF is in the stock housing and it reads 500 period that means x air flow. If you take that same air mass and pass it through a larger housing it will be less dense. less density means less cooling effect on the hot wire. This means periods for the same air mass should be higher. If you say 500 period = 1.5x air flow in a bigger pipe you are accomplishing this. you could also say x air flow = 750 period and still accomplish the same result. In a larger tube the MAF will require less frequency to maintain hot wire temperature. This would mean it would operate at relatively higher periods in a larger housing. When the ratio is applied to the air flow it expands the resolution or the air flow which is not necessary. If we apply the correction values to the period instead of the air flow it should shift the resolution of the period in a more accurate position for aftermarket modifications.

attachment to shows period modification(1.38) vs air flow modification(1.38) vs stock. Notice how the resolution of the air flow in commonly used areas(1lb/min-55lb/min) is affected.

CurveMAF.PNG

Great info Murfie! I never understood why period and airflow went in opposite directions.

[RSlo]

Copy all results, paste special multiply by % - Half

I've seen it before but why minus the half? Thanks!

[AKDMB]

I've seen it before but why minus the half? Thanks!

This is common for many tune changes, this is just to make sure you don't "overshoot" with your correction and start going in the wrong direction. Most people do this so they don't make too big of a change and so they can verify they're moving in the right direction first. It's advisable to not make big sweeping changes, but instead incremental ones, see how the car responds and keep going. This doesn't really apply so much for a base tune(accounting for a new intake by doing the calculations shown on the first page and also here http://www.hptuners.com/forum/showth...F-tuning/page7), you're probably safe making a big change there just to get started. This more or less applies for fine tuning and messing with tables where you're unsure of what impacts your tune changes will make.

[RSlo]

Cool. Thanks. The actual drop down with paste special is nice. Thought I would have to manually put in the formula.

[Jn2]

Cool. Thanks. The actual drop down with paste special is nice. Thought I would have to manually put in the formula.

Yeah it's super easy once you copy it from your histogram. Like AKDM mentioned, you want to multiply by half so you don't apply a change that moves your trims too much in one direction. Since the histogram shows averages, at certain loads and rpm's it will be too drastic of a change and push your trims too much in one direction. Hard to explain, but don't obsess over a percent flat 0 LTFT because thats not going to happen. I have mine within around -2 through -1 during DD.

[idxsky]

I know this is a topic from a few years ago, but I've been trying to tune my MAFvsPeriod and I am running against walls all the time. i am a bit scared something might be wrong since my Long term fuel trims seam way to big...
Can someone give a look at my tables and tell me what am i doing wrong ? i cannot populate my tables properly, so I cant just grab the values and use the option to multiply % -half
i appreciate any comments and help you guys can give me.
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[suprmario96]

go read the 2nd post carefully, your answer is there

[LightingBlue17]

Is the general and plot tab what is populating in the histogram as you drive basically showing you what the % is thats off and that is the data you do the half % into your MAF period table?

[Khaos_5.0]

Depends on how far off your MAF is, most likely, with a base adjustment the car will be fairly driveable. If so, you can use LTFT's. I don't know if this is a simple, use STFT or LTFT question, but I thought I might as well include the how to info.

Take your stock inner intake tube diameter, assuming you have a 5.0 Coyote Mustang, it has a stock inner intake tube diameter of 86mm (inner radius of 43mm)

The surface area of the inside of the intake tube can be calculated using pir^2 : (pi)(43^2) = 5808.8

Take the inner tube diameter of the new intake, assuming you have a JLT Intake, has a inner tube diameter of 107mm(inner radius of 53.5mm)

The surface area of the inside of the intake tube can be calculated using pir^2 : (pi)(53.5^2) = 8992.02

8992.02 /5808.8 = 1.548

Multiply the entire MAF Airflow vs. Period table by 1.548 and flash this tune to the car. Doing this with my V6 Mustang right away got the MAF Curve within 3% in most driving conditions, but the car was 12% rich at idle, so there was still work to do.There is no need to disable any form of adaptive learning in the tune when using LTFT's, which is nice. STFT's switch quick and LTFT's consistently build fueling correction. Also if I don't datalog the car, the computer does it for me by remembering the LTFT during different driving conditions, the next time I datalog the car, the learned LTFT data is there.

The next thing to do after that base correction is made, is to setup a histogram to log MAF Period.

2.25 Scanner may or may not support all of the parameters needed to tune the MAF, here is how I did it in 2.24

1. Define a custom PID for MAF Period
Attachment 54111


2. Setup the table display to include the following parameters at a minimum: LTFTB1(SAE),LTFTB2(SAE),MAF Hz and the user defined PID you created for MAF Period.


3. Setup a histogram to relate LTFT's to MAF Period.

General & Plot
Attachment 54112


Row & Col Axis
The data in the labels box is simply copied from the period axis inside the MAF Airflow vs. Period Table in your tune. You have to use commas in between values in the labels box!
Attachment 54113


4. Go on a drive, let the car learn and generate LTFT data in as many different driving conditions as possible. As it records, it will populate your histogram table. You can now use this data to tune your MAF.
Attachment 54114

This is common for many tune changes, this is just to make sure you don't "overshoot" with your correction and start going in the wrong direction. Most people do this so they don't make too big of a change and so they can verify they're moving in the right direction first. It's advisable to not make big sweeping changes, but instead incremental ones, see how the car responds and keep going. This doesn't really apply so much for a base tune(accounting for a new intake by doing the calculations shown on the first page and also here http://www.hptuners.com/forum/showth...F-tuning/page7), you're probably safe making a big change there just to get started. This more or less applies for fine tuning and messing with tables where you're unsure of what impacts your tune changes will make.

I must be missing something I created a table for maf period vs stft and when the table displays I only ever see the first frequency ever change I don?t get a complete graph.

[Pistol_91]

If its only populating one cell you probably dont have it in your channels

Screenshot 2023-08-01 211847.png