Is Your Car Tuned Correctly?

91svtbird

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The Foundation of Mass Air Calibration

The MAF Meter and it’s Transfer Functions….. The Foundation of your Tune.


My reason for posting this information is my concern for the unsuspecting Mustang community, to hopefully educate because of what I see happening with member’s cars with aftermarket tunes.

I’ve seen member’s who only have minor modifications such as New Throttle Body, Cold Air Intake, and a Tune. This has lead to part throttle pinging, and or hanging idle drive-ability issues and in some cases even with failed rods (both forged steel and powder forged). It has been suggested by some that they need to run race fuel and that will correct or prevent the problem even though they may be running a “safe” (low timing) 91 octane tune.

After checking for all the easy and basic things that could be wrong with basic installation issues such as a vacuum leak, intake tube leak etc and eliminating them, I would suggest to you that you consider looking at the way your tuner does his tuning specifically regarding the Mass Air meter curve because many of these symptoms can indicate an incorrect meter curve has been installed in your PCM.

It’s because these issues seem to be so prevalent today even more so than in earlier years I thought I'd post this information gathered and written with help from experts on this topic. I thought I’d offer a basic explanation about the role the MAF plays in tuning in a modern Mass Air vehicle and illustrate why it is so important the MAF transfer functions be calculated properly and accurately so as to reflect a true and accurate measurement of incoming air to the engine. This is the foundation of the tune.

Remember all major PCM calculations are made based on and compared to the true and accurate measurement of all incoming air by the MAF. If the meter curve is inaccurate in any way, all PCM calculations that depend upon that reading will in turn be inaccurate. Remember, garbage in garbage out.

The list of parameters dependent on a true MAF reading is long but I can assure you that every calculation depends on that air flow measurement being real and accurate.

Here are a couple of the most important parameters that are calculated from the intake airflow the MAF meter measures.
(1) Load (which is extremely critical for timing)
(2) Torque calculation. (Extremely important with Electronic Throttle (ETC) systems)
.




In the 2012 Ford Racing Part’s Catalog Ford mentions Two Tuning methods:

The First is using a MAF meter that “fools” the PCM. The Second is changing the calibration to match the hardware that is installed on the engine.
When dealing with modern ETC engine management systems, one of these methods mentioned is acceptable and preferred while the other is definitely not. The question is why one and not the other. Obviously Ford is concerned enough and seen enough of what the aftermarket has been doing that they felt it necessary to point out the differences between the two and printed it in their parts catalog.

I will direct you to the 2012 catalog Ford Racing Catalog pay close attention to page 206
http://d27vj430nutdmd.cloudfront.net/20544/88199/88199.1.pdf (hope this link is OK with the management)

“Quotes” below are from the 2012 Ford Racing parts catalog page 206

The first method mentioned is the one NOT recommended for an ETC engine management system and really isn’t the best for any system but you could get away with it on the older mass air systems with less sophisticated software. Unfortunately many of the tuners today are using a form of this method when they “move or alter” the meter curve to obtain their desired Air Fuel (A/F) but the adverse affects are the just same. Notice that Ford is careful to point out what happens to many of the other variables in the tune such as “Load” and “spark” if the MAF output signal isn’t absolutely spot on and correct. (either too high or too low)

Quote>“The first method requires a MAF sensor that has been “curved” to a certain flow rate of injector. For instance, let’s say your engine originally came with 19 lb/hr injectors and you replaced them with 39 lb/hr injectors. To use this method, you will need a MAF with electronics that have been modified such that it will output a signal proportional to an airflow that is 19/39 times as great as the stock MAF would measure. This will result in the PCM delivering the correct amount of fuel despite the fact that the injector size has been increased from 19 lb/hr to 39 lb/hr. The downside of this method is that many other variables such as spark advance are determined from the MAF sensor through a parameter called “load”. For a given engine RPM, as load increases, required spark advance decreases. Since, by using this method, the MAF outputs a signal that is lower than the stock MAF, the calculated load will also be lower. This means that commanded spark advance will be higher than it should be, which can potentially result in spark knock and other concerns. While this method works quite well on less-sophisticated electronics, such as the EEC-IV found in a Fox body Mustang, it is not recommended for newer vehicles which have a much higher dependency on the calculated value of load.”

The part above I want you to pay special attention to is highlighted in “yellow” because it points out what happens if the MAF calculations are off.



OK Now lets take a look at the “Preferred Method”

QUOTE-“The second, and much preferred method requires the ability to alter the calibration inside the PCM. When using this method, the actual flow data for the injector, as well as the “transfer function” for the MAF are entered into the calibration in the PCM .”

In Ford’s “Preferred method” (quoted above) it clearly states the importance of starting by “entering” “real actual flow data” for both the injector’s but most importantly the “Transfer Functions for the MAF” into the PCM.

You might ask how Ford acquires their “Transfer Functions” for a given application. The answer is by using a professional “flow bench” capable of accurately measuring the full range of air that meter/sensor assembly is capable of flowing. Then plotting those calculations to where they become the exact “transfer functions”. These are either the 0-5 volt signals for analog MAF meters or frequency for digital MAF meters, now being used in all Mustangs starting in 2011. This will tell you exactly how much air is measured to a corresponding voltage or frequency throughout the complete airflow range of that meter.

Understanding the correct way to achieve a real calibration for a mass air meter is critically important before taking that transfer function and entering it in the tune. Once that has been done then the rest of the parameters wanted/needed to change in the tune can be safely re-calibrated (as indicated in the Ford racing catalog as quoted below)


(2nd method continued) Quote>"Generally, it is recommended to test the new calibration on a dynamometer to ensure that the engine receives the correct A/F ratio at all speeds and loads. Provided this is performed by a competent and experienced operator using proper equipment, this is by far the best method and will result in the best part-throttle drivability and idle, and the least amount of trouble with check-engine lights, returnless fuel, electronic throttle monitors, transmission shifting, etc.”

It is always best to dyno the engine to check A/F but altering the MAF transfer functions is not the proper way to make corrections if any are needed to achieve target air fuel.

With a known actual meter curve/transfer functions already installed in the PCM it is proper and far better to make small incremental changes to injector slopes and or other fuel maps which would only affect the A/F and not load.

Whereas changing the MAF transfer functions (MAF meter curve) to reach target A/F would indeed affect load and many other parameters like spark advance, throttle blade openings, dashpots, torque tables etc. (as indicated in Yellow in Ford’s method #1 above)

Unfortunately many tuners today are indeed altering the MAF to adjust for target A/F. I believe this is the main reason why we see many cars “pinging” at part throttle even though the newer engines have knock sensors and wide band O2’s that would normally prevent such an occurrence. (The load tables are likely incorrect because the meter curve is not reading “actual flow data” causing the spark tables to add too much timing.)

For example it is quite possible depending how incorrect the load tables are instead of calling for 18* of timing it could be calling for 30* or more at a given throttle position. This would lead to detonation and possible engine damage. I believe we could already be seeing this happen in some cases. When it does the answer to the customer is to add a can or two of octane booster because they are using “bad gas”.


ETC (Drive by wire)
Having the MAF meter curve absolutely correct and reflective of “actual air flow data” is especially critical with ETC systems. Ford relies very much on accurate mass air data to determine load which in turn will dictate throttle body blade closure under certain circumstances when torque limits are exceeded. This is even more important now that the much more accurate “Digital meters” are being used. Among other data the PCM is always checking and comparing data between the MAF and the TPS to determine correct throttle position. If that information being delivered is incorrect or it could likely result in drivability problems such as a hanging or hunting idle, even codes or a failsafe condition. Of course the customer and or tuner will then think there is something wrong with the TB instead of looking at the real culprit…the inaccurate meter curve.

Alternate ways of creating a meter curve?
When one tries to create a mass air transfer function table in a tune where the CAI, pumps injectors etc were all changed at the same time would be impossible to do so accurately. This is because there is no real flow data on the fuel system or the mass air meter.

When they do most of the calibrating in the tune by changing the meter transfer curve to obtain the air fuel ratio they would have no clue what that meter is telling the computer airflow wise, all they care about and looking at is one thing, air fuel ratio coming out the tail pipe.
The A/F ratio may be correct, however, other items such as torque demand, spark advance, etc will be grossly incorrect. I also believe this is why when a tuner does move a transfer curve around in a tune without knowing its true flow, they get some cars to run good (no problems) and others with all kinds of little drivability issues . Further, those drivability issues are often blamed by the tuner on some part the guy changed in the car but rarely the tune itself.

Checking MAF voltage/frequency when data logging is important for a few reasons.
(1) Do not exceed the range of the sensor.
(2) It is also used in checking the amount of airflow the motor is moving at a certain RPM.
(3)Airflow is a needed known parameter to understand fuel requirements.
(Also great info when a blower, cams or anything that can improve airflow is changed) Airflow is power, valuable data to record if you want to know what kind of power your engine is making.


Understanding the need for a correct mass air calibration transfer curve to be entered into a tune instead of trying to calibrate/create the mass air sensor transfer function on/in the car (Adjusting it without realizing all the other factors) is critical.

Calibrating a mass air meter and calibrating a complete tune are two different things but one should be starting off with the correctly calibrated transfer function first.

Why Ford sells their meter housings without providing transfer functions
Ford sells larger MAF meter housings in their catalog without providing the transfer functions. This is because there are many different applications these meters can be used in. There is no way Ford could know which tube or filter one might be using with a particular meter housing. Ford leaves it up to the tuner/car owner and expects they will get their particular combo of filter, meter, sensor and tube flowed and calibrated on a professional flow bench to ensure the proper transfer functions the same way they (Ford) does.
To suggest that the meter curve be done on a chassis dyno by using short term fuel trims at idle and part throttle rpm’s and scaling up from there is virtually guessing the complete voltage/frequency range of the meter and can be a highly risky and dangerous practice.

With regard to Ford “kits” which include a filter, sensor, meter housing and tube, Ford does all the work for you as they do indeed include the proper transfer functions in their tune.
Quote>“Ford Racing performance upgrade kits and their associated calibrations are designed to work together seamlessly, taking much of the hard work out of upgrading
the performance of your vehicle.”


It all goes back to understanding things from the foundation up, not starting on the top floor and trying to work down. The MAF transfer functions are the foundation!

Ford also provides the known flow data for both the injectors and the MAF. They do not alter or change the “meter curve” in their kits from one vehicle to another for a given vehicle like is being done by many tuners today because their data is “actual flow data” determined using a professional flow bench.

Moving a transfer curve around (instead of using real flow data) is like calibrating a torque wrench by feel. (How accurate is that?)

Believe the myths in the aftermarket or not it is your call and it’s your engine that could be at risk. Many have already found out too late and some still today are blaming it on bad gas or faulty parts.

How to know if your tuner alters the MAF
If you want to know if your tuner alters the meter curve when he tunes or if he establishes his MAF meter curve on a chassis dyno using short term fuel trims instead of having it flowed on a professional flow bench or if your tuner alters a known meter curve to adjust for A/F then I suggest you ask him. Most of the tuners that do it that way absolutely believe it is the correct way to tune because they have been taught that from the aftermarket software companies so they most likely will tell you if they do.

Another simple way to tell if your tuner has altered your MAF or entered an incorrect MAF transfer map would be to see if your factory boost gauge is not reading correctly anymore compared to say, an accurate mechanical gauge or even from one tune to another in the same car all things being equal.

You might ask what does that have to do with the MAF being incorrect? The answer is because the factory boost reading is based on calculations directly off the MAF readings at any given RPM. Remember the MAF should be and is dependent upon measuring real accurate airflow.

Lets say for example (using volts):

1 volt is a 100 cfm

2 volts is 200 cfm

and so on up to 5 volts.

Your boost gauge value is calculated from the MAF transfer curve to tell it how much air the motor is moving and converts it into a boost value (It does use other sensors also to do this but it all starts with the reading from the MAF)

A tune that is causing the gauge to read a higher boost value than it should is actually telling the PCM its moving more air than it actually is .

So instead of 1 volt representing a 100 cfm as stated above the incorrect MAF tune 1 volt is representing 110 cfm.
Since the boost gauge depends on all of its calculations beginning with those values’ any tune telling the computer it is moving more air will read a higher boost value.

This itself isn’t critical but is indicative of the bigger problem that you have which is that your car is now likely running with all parameters in the tune being dangerously OFF especially the spark (timing) tables………



Finally this article may be contrary to most of the aftermarket establishments but as we’ve seen I don’t believe it is to the calibrators at Ford. I do hope it will be a help to those who want to ensure they have a safe tune and enjoy driving a car that drives the way it was engineered to drive. I would also hope that the aftermarket in general will take heed and start their tune with a real and accurate MAF transfer curve and not routinely alter it as their standard way of tuning putting your engine’s life is at risk in the process.


Respectfully,

George Brower

Special thanks to PCM and MAF consultant Jim Larocca and Sam Guido (PCM software developer for FMCO) for their expertise and contributions to this article.
 
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railroad

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Well, my next question would be, who uses which method?
I have heard good things about Larocca.
 

03Steve

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Most of this knowledge is spot on, other is dated. One example of the dated:

For instance, let’s say your engine originally came with 19 lb/hr injectors and you replaced them with 39 lb/hr injectors. To use this method, you will need a MAF with electronics that have been modified such that it will output a signal proportional to an airflow that is 19/39 times as great as the stock MAF would measure. This will result in the PCM delivering the correct amount of fuel despite the fact that the injector size has been increased from 19 lb/hr to 39 lb/hr.

Correction: You can run any MAF with any injector.

Let's say you are running a stock car with 15psi of boost. You decide you want to use E98 fuel. In part you may need bigger injectors, correct? This doesn't mean the MAF has to change to match the injectors. The MAF does not need to match the injectors. The MAF does need to have enough range to measure the airflow present.

If you want to know if your tuner alters the meter curve when he tunes or if he establishes his MAF meter curve on a chassis dyno using short term fuel trims instead of having it flowed on a professional flow bench or if your tuner alters a known meter curve to adjust for A/F then I suggest you ask him. Most of the tuners that do it that way absolutely believe it is the correct way to tune because they have been taught that from the aftermarket software companies so they most likely will tell you if they do.

If the starting point for the air model is correct, then yes...the MAF transfer/freq function remains untouched. How many people are receiving flow sheets with the MAF they buy? I did with my Pro-M.

Some food for thought...

When I tuned my current engine combination, I started with a stock 03 Cobra MAF. I put the car down to the minimum boost setting, and worked with a stock 03 Cobra MAF transfer function. With the car having cams, aftermarket injectors, and other mods...I first addressed them knowing that the air model I currently had was spot on. With everything else addressed, I then installed the Pro-M MAF with the flow sheet that was built for that MAF and air filter, along with the data from the flow sheet into the calibration. Air/fuel and load did not change.
 

91svtbird

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Most of this knowledge is spot on, other is dated. One example of the dated:



Correction: You can run any MAF with any injector.

Let's say you are running a stock car with 15psi of boost. You decide you want to use E98 fuel. In part you may need bigger injectors, correct? This doesn't mean the MAF has to change to match the injectors. The MAF does not need to match the injectors. The MAF does need to have enough range to measure the airflow present.



If the starting point for the air model is correct, then yes...the MAF transfer/freq function remains untouched. How many people are receiving flow sheets with the MAF they buy? I did with my Pro-M.

Some food for thought...

When I tuned my current engine combination, I started with a stock 03 Cobra MAF. I put the car down to the minimum boost setting, and worked with a stock 03 Cobra MAF transfer function. With the car having cams, aftermarket injectors, and other mods...I first addressed them knowing that the air model I currently had was spot on. With everything else addressed, I then installed the Pro-M MAF with the flow sheet that was built for that MAF and air filter, along with the data from the flow sheet into the calibration. Air/fuel and load did not change.

Yeah that was the example Ford used. Of course my aim was to show that the negative effects on the overall tune are the same when altering a known MAF meter curve.

Glad to see you understand that as evidenced by after having flowed your pro M meter and using that data in your tune the A/F was spot on. WTG !
 

Ryan23

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So, for the sake of simplicity, wouldn't the safest course of action be to just retain the factory intake tube & just add a resonator delete/larger element filter?

With the sensor calibration being such a critical element, it seems like the stock MAF location would always be spot on. Is there any real benefit to changing the pre-blower piping, all tuning being equal?

Ryan
 

91svtbird

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So, for the sake of simplicity, wouldn't the safest course of action be to just retain the factory intake tube & just add a resonator delete/larger element filter?

With the sensor calibration being such a critical element, it seems like the stock MAF location would always be spot on. Is there any real benefit to changing the pre-blower piping, all tuning being equal?

Ryan

That would be fine as long as the HP level increased by the new modifications doesn't take the airflow level past the maximum range of the stock MAF meter,tube and sensor combo. (which on the 13' is roughly around the 640-650 rwhp range) Then a larger MAF housing assembly would be needed.
If the transfer functions are obtained as mentioned in the article above it would operate exactly like the stock one does only with extended range which would allow it to support additional airflow.
 

ALLKHEINZ

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Jim Larocca and Dennis from Tasca Ford tuned my gt500 and i would never go to anyone else ever again. PERIOD!
 

TClark22

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pretty sure mines not tuned correctly...but i don't know any good tuners in the KC area.

Mine drives daily and has for 5 years with my procharger but it has never run well. Its a rough ride.
 

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