Calibrated MAFs are something you are almost guaranteed to run into sooner or later tuning EECIV Fords.  Although largely an artifact of yesteryear when tuning tools were not available, “calibrated” MAFs will work just as well as any other if you understand them.  Few of the websites out there will really give you the information you need to use them effectively in current golden age of EECIV tuning.

How They Work

The factory ECM has a table that tells the computer that it has a certain amount of air when there is a particular MAF voltage.  (i.e. “MAF Transfer Function”)  The computer also has a configuration for a set of injectors. (i.e. “high slope / low slope / breakpoint / offset”)  The factory ECM is going to deliver a certain amount of fuel based on the size of the injectors, MAF transfer and amount of air / voltage coming from the MAF.

So pretend for a moment that the ECM is off limits.  You can’t do anything with the MAF transfer function or any of the internal configuration.  But you need to be able to support a larger engine that makes more power than factory 19# injectors can support.  So you install 24# injectors that flow more fuel.  Paired with a stock MAF, 24# injectors are going to make the car run really rich!  Mass air flow (output from MAF transfer) x injector slopes get’s you pulsewidth, pulsewidth determines fuel flow.  You can’t change anything on the computer in this game, so what do you do to fix fueling?

Enter the calibrated MAF.

Say you start with a system that uses 19# injectors and you have installed 24# injectors.  Your injectors flow roughly (24# / 19#) or 1.26 times too much fuel.  What’s the other side of the fueling equation?  Airflow.  If you can make the MAF output 1.26 times LESS air, the net amount of fuel will be about the same as when you have a factory MAF and factory injectors.  “Calibrated MAFs” diddle with the voltage->airflow output of the MAF in order to try and make a factory ECM provide the correct amount of fueling without needing any of its program being altered.  Essentially, hardware modifications to the sampling tube and electrical tweaks are used to produce a specifically reshaped output to fool the ECM into somewhat behaving.

So What Does This Mean?

There is an unintended consequence to using a “Calibrated MAF” setup.  In addition to being used for fueling, the MAF is also used to calculate timing at part throttle.  Less air means less Load.  Less Load generally means more timing at part throttle.  Fortunately, the WOT timing model of factory fox body cars removes most of the danger inherent with changing Load values without changing the rest of the tune.   It’s an imperfect system, at best.  There are generally errors here and there in the airflow curve.  Hopefully, they’re small enough to be corrected by O2 sensors.  Remember, this whole matching calibrated MAF thing dates to when there weren’t tuning options commonly available.

In the golden age of EECIV tuning ushered in by the QuarterHorse, you can make effective changes to the calibration on the ECM, removing the need for MAFs to be “Calibrated” in hardware.  Instead, the quality of MAF calibration will depend on how closely the values you have programmed in the MAF transfer function match the actual airflow values required to produce given voltages.  Being able to independently change the MAF transfer function and injector configuration using our tools removes the need for the “calibration” to be done in hardware and instead lets you do it in software by tuning the vehicle and modifying its calibration.

Bottom line: when tuning with a QuarterHorse, the flow test or flow sheet from the MAF is 100x more important than the MAF being “calibrated” for whatever injectors are being used.  The MAF and injectors can be independently calibrated in tuning software.

References

C+L on Calibrated MAFs

Need more refs…

The rise of electronic engine management allows for the running conditions of an engine to be rapidly and precisely adjusted.  Before we talk about anything super technical, it’s worth examining some really basic stuff like, “why should we bother tuning a car in the first place?”  “What can we reasonably hope to accomplish?”

Sometimes we start with an engine that’s running acceptably but we want to slightly change how it operates to achieve our goals.  Sometimes we start with an engine that doesn’t run at all because it is so different from the original system that was running that we have to tune it for it to run acceptably.  Regardless of whether adjustments are made out of necessity or desire, the answer to this “why bother” question is simple: in a word, it is OPTIMIZATION.  Tuning allows us to make the most out of the engine that we have.

What Tuning ISN’T

Tuning cars is often very misunderstood, especially by people who do not do it.  There is no magic involved.  You cannot wave a magic wand and violate the laws of physics in the name of making horsepower.  You are dealing with a computer system that responds to sensors in a predictable way.

There is one golden rule (which I think has its origins in a completely different realm) which applies here:

Garbage In, Garbage Out.

As a tuner, you can only work with what you are given.   This may seem so obvious that it is a waste of time to even say it.  Trust me.  It isn’t.  It’s critical.  And at some point if you mess around with tuning vehicles long enough, you will get so focused on the knobs and buttons available to turn on your computer that you will forget about the mechanical system you are controlling.

• Changing a computer program can’t fix mechanical issues.
• Changing a computer program can’t fix electrical issues.
• Changing a computer program can’t make more air enter an engine than it can mechanically pump
• Changing a computer program can’t make more fuel flow through pumps/injectors than they can mechanically pump
• Bottom line: You can’t make pigs fly by pushing buttons.  The physical motor you are working with will define what you do on the computer.

Tuning Possibilities

So if we are inherently limited by the physical engine that we are dealing with, what CAN we typically accomplish with tuning?

Typically, we can:

• Increase power / torque output of the engine
• Increase efficiency / decrease fuel consumption
• Decrease noxious emissions (Carbon Dioxide/CO2, hydrocarbons/HC, Carbon Monoxide/CO, Nitrous oxide/N2O, Nitrogen Oxides/NOx)
• Control NVH (Noise – Vibration – Harshness)
• Decrease stress on mechanical components / prevent damage to mechanical components
• Many of these goals require different operating conditions making it impossible to do all of them at once! 

Conclusion

Tuning isn’t magic.  Modifying electronic engine control systems lets you get the most out of the physical system that you’re working with.  Through tuning, you can choose how to operate an engine in order to achieve the goals that are most important to you, making the compromises you want to make.  The goal of this course is going to be to teach you to use a calculator/simple math and data logging combined with an understanding of underlying processes to make targeted and appropriate changes in order to achieve the operating conditions you desire for your engine.

The material in this course represents *hours* (think: whole day+) worth of classroom lecture and discussion. Be prepared to spend an extended period of time reading through it and processing it. When you’re done, you’ll arguably be better prepared to tackle tuning than half the shops that practice on your car.

Enjoy!

(More will be coming soon as time permits.)