Ford: “Calibrated” MAFs


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.


C+L on Calibrated MAFs

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