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

Old 03-21-2009, 05:44 PM
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How to Scale your MAF for Flash Tuning (Cobb, Hymee)

Ok - I am finally going to sit down and try to spell this one out as best I can.

With our MAF based car tuning you have two "running numbers"; the fuel flow and the airflow. Once you start to play around with these (or even from the factory) they start to vary from thier intended Volts to Value tables.

Before we address the Fuel Scaling - the first step in tuning a MAF car is to Scale the MAF. This involves correcting the MAF table from the g/sec or lb/min values and the voltage readings.



Here is a screenshot of a sample MAF Scale.

Step One: Cruising.
- On your Base Fueling MAP; set the Lamda Values in the cruising range to 1 (AFR 14.7). Be sure to use the LOW LOAD areas in order to avoid engine damage. Additionally; you will need to ensure you are in Open Loop.
- For Closed Loop areas; set the lamda to 1 and compare your Fuel Trims to the % changes you are making in open loop. See more info on this below.
- Go find a flat level surface or dyno and get your car into a stable cruising speed and RPM. Hold it long enough for your AFR's to become stable. Document the Volts, g/sec, measured Lamda like in the picture above.
- You can also log these runs and go over the average (like Baseline Does).
- Adjust your g/sec based on the % deviation from your target. Using a Target Lamda of 1 makes the math easier.
- Hit as many voltage cells as you can in your Low Load cruising areas and look for trends. If your 1-3 Voltage range is all trending low by 10%; go ahead and scale the ENTIRE MAF by that percentage in order to get closer to your targets when you do your WOT MAF Scaling.
- Once you get all your crusing areas within 1-2 Percent then you should be pretty good.

Step Two: WOT / Boost
- The process is basically the same but your obviously NOT going to set your Lambda to 1.... set your target Lambda to a safe number (this AFTER you may have already scaled the entire MAF by the percentage trend in the Cruising Area.)
- Zero the Throttle Enrichment Maps out - you just want to see the Base Map Fueling.
- Be careful about stabbing the GO Pedal; since your gonna get lean spikes without Enrichment.
- Get to your higher Load Areas - Boost and WOT; but don't Punch the pedal, slowly get to WOT and hold it as long as you can.
- Use the same Math Process as Cruising but with a richer Lamda.

Step Three: Connect the Dots.
- Now that you have maybe 40-60% of your MAF scale done; connect the dots by filling in the blanks using the overall shape of your MAF curve.
- Try to make a nice smooth line. You can go back and re-tune the blanks later if you need to.
- Ideally you want to test each voltage in your table; but some interpollation is not going to be a big deal.

Step Four: Idle
- With radical cams / porting idle can be an issue.... the best way to go here is to get a g/sec trend for your car. Like the RX8; all 10-20 stock and boosted ones I have seen, all idle really close to 5 g/sec... so if your car idle g/sec is 7-8 then you can adjust it down to a known approximate value of (in my case 5). If your MAF numbers never get stable; you need to address the turbulence. If your engine is modifyed to the point you can never get it stable; then just do your best and shoot ffor best idle quality.
- You always do idle last because it can be the most challenging; but again if your % changes were all pretty much the same across the board then you can start with that % change at idle as well.

* Remember you don't have to have the same numbers or trendline; if your cruising is scaled at 3-5% and your WOT areas end up being scaled at 15%; that is fine.
* Closed loop actual lambda readings can't be used since the car will hit the target Lamda using Fuel Trims. So in closed loop cruising; look at your logged and stable LTFT instead.

Tuning ANY FUEL MAPS without first knowing your airflow readings are good is a waste - get your sensors right FIRST; then start in on your actual tuning.


Scaling the Fuel Injectors is a bit-o-pain since we have some that only come on later on. As fo the primary injector; use your "known" MAF g/sec value and look at your fuel trims... if your MAF idle is 5 g/sec (good based on known similar cars) and your LTFT is +5%; there is a good chance that is the Fuel Injector scale.... go back and scale the P1 injector a bit and see if it cures it.


I am attaching a sample Excel Spreadsheet you can use to get started.
Attached Files
File Type: zip
MAF Scaling.xls.zip (5.7 KB, 906 views)
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Old 03-21-2009, 06:51 PM
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this is nice kane!
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Old 03-21-2009, 06:55 PM
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I hope it makes sense.... I talked a few guys through it over the phone - but I was trying to consolodate it into some easier steps.

The big question is when the Air Scaling turn to Fuel Scaling... and short of flow testing your injectors - some educated guessing has to go down.

I'm gonna try a few techniques and get back to you on the Fuel Stuff.
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Old 03-21-2009, 07:51 PM
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Great info!

dumb question how do you know what is open loop and closed loop?
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Old 03-21-2009, 09:04 PM
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Nice. Lets automate that!

Cheers,
Hymee.
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Old 03-21-2009, 09:33 PM
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wow kane I like that a lot, specially since im beginning to maybe want to tune my car with the street tuner and one of the local tuners, so having this info is nice. Thanks!
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Old 03-22-2009, 12:43 AM
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sticky!
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Old 03-22-2009, 01:11 AM
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MAF Calibration for new Induction kit

In order to correctly calibrate the ECU for the new induction kit, the relationship between air flow and output voltage of the air flow sensor must be measured. Initial thoughts would suggest using a flow bench to do this, though very few tuners will have access to a calibrated flow bench capable of flowing 300 grams per second of air.

In actual fact, all tuners do in fact have this flow bench in their workshops - the vehicle itself ! By plumbing the the two induction kits in series (the standard system and the new system), it is possible to draw the same mass of air through each induction kit. With a mass air flow sensor in each induction kit, it is possible to measure the sensor output from each kit. By taking the vehicle through a wide air flow range on the dyno, it is possible to measure the relative outputs of the two sensors when mounted in the two induction kits. A tool such as DelatDash External Sensor Logging may then be used to record the data for later analysis.

The result of recording this data is a graph showing the relative outputs of the two induction kits for a range of air flows.
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Old 03-22-2009, 04:54 AM
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Originally Posted by Hymee View Post
Nice. Lets automate that!

Cheers,
Hymee.
No; that will NEVER work!

You do your part and I'll do mine!

Originally Posted by a_ahlan View Post
In order to correctly calibrate the ECU for the new induction kit, the relationship between air flow and output voltage of the air flow sensor must be measured. Initial thoughts would suggest using a flow bench to do this, though very few tuners will have access to a calibrated flow bench capable of flowing 300 grams per second of air.

In actual fact, all tuners do in fact have this flow bench in their workshops - the vehicle itself ! By plumbing the the two induction kits in series (the standard system and the new system), it is possible to draw the same mass of air through each induction kit. With a mass air flow sensor in each induction kit, it is possible to measure the sensor output from each kit. By taking the vehicle through a wide air flow range on the dyno, it is possible to measure the relative outputs of the two sensors when mounted in the two induction kits. A tool such as DelatDash External Sensor Logging may then be used to record the data for later analysis.

The result of recording this data is a graph showing the relative outputs of the two induction kits for a range of air flows.
Huh? Parallel logging seems kind of a waste of time in most cases as we have a feedback loop already.
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Old 03-22-2009, 04:56 AM
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BTW - can an admin fix my crappy spelling on the title... I fail.
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Old 03-22-2009, 05:11 AM
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Originally Posted by rotarenvy View Post
Great info!

dumb question how do you know what is open loop and closed loop?
WOT and above 4000 RPMS or so is open loop.

There is a load threshold too - but I don't know it....
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Old 03-22-2009, 05:52 AM
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Originally Posted by rotarenvy View Post
Great info!

dumb question how do you know what is open loop and closed loop?
What Kane said, plus a couple of other things...

You can see it with a sCAN tool... (??) as one of the params monitored is "fuel system status".

You can also generally see it in logging - when the lambda is around 1.0 give or take a small amount, then it is closed loop. When she drops out of closed loop, lambda will generally be nowhere near 1.0 (consistently).

Cheers,
Hymee.
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Old 03-22-2009, 10:58 AM
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I'm just going to blurt out my opinion on maf tuning here...

If your maf is reading around 5-6 g/s at idle, has a steady voltage output at idle and light cruise, and if the max flow (normally aspirated) is around 210-220ish g/s then there is no use in touching the maf. If you have a stock intake there is probably no need to touch it and if you have your maf sitting in a different size pipe that should be pretty easy to accommodate with using some math.

I tried to tune only tweaking the maf last summer and all you do is end up chasing your tail.
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Old 03-22-2009, 02:22 PM
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Originally Posted by r0tor View Post
I'm just going to blurt out my opinion on maf tuning here...

If your maf is reading around 5-6 g/s at idle, has a steady voltage output at idle and light cruise, and if the max flow (normally aspirated) is around 210-220ish g/s then there is no use in touching the maf. If you have a stock intake there is probably no need to touch it and if you have your maf sitting in a different size pipe that should be pretty easy to accommodate with using some math.

I tried to tune only tweaking the maf last summer and all you do is end up chasing your tail.
If running an all stock intake - then there isn't any reason to scale the MAF....

Listen folks - this isn't tuning - this is getting accurate information to the PCM... you can't "tune" with messing with the MAF sensor - you get it right, then get your fuel injectors right, then go tune the fuel and timing tables.



Anything else is a band-aid
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Old 03-22-2009, 02:23 PM
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Originally Posted by Kane View Post
No; that will NEVER work!


Huh? Parallel logging seems kind of a waste of time in most cases as we have a feedback loop already.
The procedure I described was to recalibrate the MAF sensor when used in a new tube of a different diameter or new induction kit.
I don't see any reason for messing with MAF when the intake is a stock setup and LTFTs are perfect.
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Old 03-22-2009, 02:28 PM
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Ah I see ahlan.

Yes that would work; my process is doing the same thing just with the new induction kit already on the car.
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Old 03-22-2009, 05:01 PM
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Originally Posted by Kane View Post
If running an all stock intake - then there isn't any reason to scale the MAF....

Listen folks - this isn't tuning - this is getting accurate information to the PCM... you can't "tune" with messing with the MAF sensor - you get it right, then get your fuel injectors right, then go tune the fuel and timing tables.



Anything else is a band-aid
Well said!

Cheers,
Hymee.
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Old 03-22-2009, 05:15 PM
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Originally Posted by Kane View Post
WOT and above 4000 RPMS or so is open loop.

There is a load threshold too - but I don't know it....
I started to have a look at my logs and realized most of the cruising speeds where there is a lambda of 1 seemed to be closed loop areas.

Originally Posted by Hymee View Post
What Kane said, plus a couple of other things...

You can see it with a sCAN tool... (??) as one of the params monitored is "fuel system status".

You can also generally see it in logging - when the lambda is around 1.0 give or take a small amount, then it is closed loop. When she drops out of closed loop, lambda will generally be nowhere near 1.0 (consistently).

Cheers,
Hymee.
I'd better start sCANing
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Old 03-22-2009, 05:20 PM
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I also just read if the STFT is a fixed number - you're in open loop.

SO that is another way to tell.
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Old 03-22-2009, 05:33 PM
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The way I did it was kind ot a reverse version of Kanes , but I had no instructions so had to start somewhere .

*Made sure my LTFT had settled down
*adjusted entire maf up to 200g/s (typical N/A range) by the LTFT value . IE if LTFT was -10 i took 10% from all values up to 200g/s.
*Did some WOT logs (always monitoring AFRs real time as well) and adjusted maf to approx. get the AFRs i wanted in the ranges above 200
*fine tune with fuel maps

not saying this is any better - just another way to to it .....

BTW - I just checked my idle and it reads 5g/s

Last edited by Brettus; 03-22-2009 at 05:35 PM.
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Old 03-23-2009, 07:13 PM
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I have a question about Maf scaling? I installed a AEM intake and I expected my Maf to need recalibrated but my LTFT's are consitently at 0. I've put about a hundred miles on the car with several drive cycles and the LTFT's are still 0. With the stock intake I saw on average +7 for LTFT. Does this sound normal? My AFR's are a little off, so I'm assuming it has to be a Maf issue.
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Old 03-23-2009, 10:41 PM
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Originally Posted by po_snake View Post
I have a question about Maf scaling? I installed a AEM intake and I expected my Maf to need recalibrated but my LTFT's are consitently at 0. I've put about a hundred miles on the car with several drive cycles and the LTFT's are still 0. With the stock intake I saw on average +7 for LTFT. Does this sound normal? My AFR's are a little off, so I'm assuming it has to be a Maf issue.
AEM is a good stock type intake MAF wise....if you AFR's are off though - retune for it to be sure it is accurate.


Could also be the fuel injectors; or a combo.

Last edited by Kane; 03-23-2009 at 10:45 PM.
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Old 03-24-2009, 11:55 AM
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Originally Posted by Kane View Post
AEM is a good stock type intake MAF wise....if you AFR's are off though - retune for it to be sure it is accurate.


Could also be the fuel injectors; or a combo.
Thanks for the advise. I will take a look at the injectors.
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Old 03-24-2009, 12:18 PM
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A couple of quick points:

1) The MAF sensor's response is not linear. Its not even an exponential curve. Its response not really even a curve. Its a sorta lumpy Bézier. The response curve that is described in the PCM MAF calibration table is an "optimized" average of the expected MAF output.
2) The injector output is also not a perfect curve and changing its scaling changes the slope of that fuel delivery rate curve.
3) The fuel delivery calculation is based on load, not the MAF output, so chasing a lambda value based on the MAF reading wont work most of the time.
4) [TRADE SECRET AHEAD] Open loop is adjusted by several interacting tables based on RPM, MAF, accelerator position, vehicle speed (gear) and load. However, a quick way to force open loop is to disconnect the front O2 sensor.
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Old 03-26-2009, 12:29 AM
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Bare with me here.

First question. How can the function that describes the output of the MAF sensor, NOT be a 1:1, invertable function? I am not asking about the physics (which, at a first approximation, would suggest that such a descriptive model WOULD be invertable), but the simple fact that the pcm needs to convert voltage back to measured flux. If the function was grossly lumpy then a voltage would be potentially ambiguous, solving for two or more flows.

Second: I am trying to determine if i should proceed with MAF calibration with my current intake configuration. I have the greddy tube, however, I have pretty smooth AFR traces. HOW smooth is smooth. I dont have a problem changing intakes; however, I have more than a foot of straight pipe infront of the MAF housing prior to a ninty degree bend. I think it is pretty good. Furthermore, to smooth out the flow a little, I was considering putting in a screen Could I simply take some flexable screen and just seal it onto the maf housing with the coupler and a t-bolt clamp?

Third: what would be the best base map to start modifing? Would any functional map serve as a base?

Finally, in order to perform the MAF calibration, I need to scale my injectors as a first approximation. I know the scaling function, but how do i know these will provide a sufficiently safely rich mix in boost?

Actual final question. Seriously, how many times can I flash my PCM. I figure, I will be flashing it several hundered times in the next 6 months (the time i figure it will take me to tune.)
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