Dale Amy
June 1, 2003

Horse Sense:
While in closed-loop (part-throttle) operation, the EEC uses feedback from the car's oxygen sensors to monitor and maintain a "stoichiometric" air/fuel ratio. This ratio of around 14.7 parts air to 1 part fuel is that which produces the most thorough combustion. At wide-open throttle, or in open-loop, feedback from the O2 sensors is ignored and A/F is dictated strictly by the EEC.

Like it or not, we have the often mysterious world of electrons to thank for the modern Mustang's jaw-dropping performance potential. Were it not for the unparalleled speed and precision of electronic engine control processors when it comes to spark and air/fuel mixture, we couldn't begin to approach the blend of power, economy, and prep-school manners we've come to take for granted these days.

But a computer is only as good as its software, and, as good as they are, factory tuning calibrations aren't always perfect-even for a stock vehicle, since they're generalized and even compromised to allow for production tolerances and other variables. That gap from tuning perfection will widen to a chasm after hop-up modifications are made, because the original calibrations were based on assumptions that will no longer be valid.

Instead of using wrenches and screwdrivers to close that gap, today we must rely on "tuning" the EEC computer itself, since these days an engine does exactly what its electronic brain tells it to. Most of us are familiar with tuning via EEPROM chips-such as those from Autologic, DiabloSport, and Superchips-that go in and substitute revised data in the EEC's programming tables. Well, when it comes to manipulating air/fuel ratios, there's now another way to trick the EEC into doing our bidding: We can lie to it about how much air is inbound to the combustion chambers. Enter Pro-M's MAFtuner, which can be thought of as an air/fuel ratio tuning tool disguised as a little black box. Used properly, it can root out the last bits of power, driveability and mileage hiding in your Ford's current combination, whether heavily modified or factory stock.

The MAFtuner functions by intercepting-and modifying-the electronic signal between your car's mass airflow meter (MAF) and computer (EEC IV or EEC V). Remember that a mass air meter's one and only job is to tell the EEC processor as accurately as possible how much air is being ingested at any given time, so that the EEC can then order the appropriate amount of fuel injected for proper combustion. Maintaining an ideal ratio between air and fuel-an ideal that varies somewhat depending on a number of factors-is oh-so vital for exhaust cleanliness, idle quality, driveability, power production, and ultimately the engine's survival. An A/F ratio that is at any time either too rich or too lean can adversely affect any or all of these conditions.

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In Ford applications, the mass air meter talks to the EEC by sending it a signal that increases in voltage with the mass of incoming air. More air equals more voltage (within a range of roughly 0-5 volts DC). In the EEC's software cerebrum, any given voltage input is equated to a certain mass of air, to which the program assigns a corresponding amount of fuel to be injected. In other words, the amount of fuel injected is directly related to the voltage received by the EEC from the mass air. Raise that voltage and the computer would call for more gas, and vice versa.

The MAFtuner does its trickery by intercepting the mass air meter voltage signal and selectively raising or lowering it, according to the user's preference, before sending the modified voltage on to the EEC. This makes the computer believe that either more or less air is being ingested than is actually the case, fooling it into generating a slightly leaner or richer A/F mixture. The voltage changes applied by the user need not be universal; they can vary from point to point in the airflow curve. In other words, you can leave the mixture as is at some points, richen it in some areas, and lean it in others, depending on what your engine's combination responds to best.

These voltage alterations can be ordered up either by using the combination of four potentiometers and eight LEDs arrayed on the face of the MAFtuner, or by attaching a laptop. Since it's best to have a clear A/F ratio feedback, detailed tuning will be best done on a dyno equipped with a wideband oxygen sensor that can show the ratio real-time. But Pro-M can provide general suggestions for what has worked on particular vehicles and combinations.

The MAFtuner can also save you from needing to have your meter recalibrated after changing injector sizes or adding a cold-air kit. For instance, let's say you have a 75mm Bullet mass air calibrated for stock 19-lb/hr injectors and you then upgrade to a set of 24-lb/hr squirters. Rather than removing and shipping your meter back to the manufacturer for recalibration, you can simply hook up your MAFtuner to your laptop with the supplied cable, and use the included software to reprogram it using specific voltage alteration tables available from Pro-M.

Will the MAFtuner completely eliminate the need for chip tuning or an EEC reflash after radical engine mods such as ported heads and a blower? No, it won't, because it can address only the fuel side of the tuning equation and not the spark. But it does add real-time A/F tuning to your bag of tricks. Will the mere act of bolting on the MAFtuner instantly gain you horsepower? Nope, it's a tuning tool, not a power adder. But it's a flexible way to gain complete control over all-important air/fuel mixtures, and getting those right can maximize power, driveability, and efficiency, making the MAFtuner a valuable addition to your tuning arsenal.

OK, So How Do I Use It?
Once the MAFtuner is installed, MAF voltage as seen by the EEC-and therefore air/fuel ratios-can be adjusted via programming, or in real-time. The former is done with a laptop, the latter, without. Real-time adjustment can be performed with the engine running, using the unit's four potentiometers and octet of LEDs. Roughly speaking, the left-most knob adjusts idle mixture, the middle-two are for midflow, and the right knob alters voltage at maximum airflow. The LEDs beneath indicate where you are in the MAF's voltage range (showing a percentage of maximum airflow). Let's say you have your car on a chassis dyno with a wide-band oxygen sensor attached. If the wide-band's display shows a rich or lean A/F ratio at a certain point during a pull, a glance at the LEDs will tell which pot to adjust to correct it-just turn the knob above whichever LED is lit to alter mixture at that point. Turning the knob clockwise increases the voltage sent to the EEC (enriching the mixture), and counterclockwise decreases it (leaning the mixture). Naturally, the logical question is, how do you know when the mixture is too rich or too lean? There can, of course, be overall clues in spark-plug condition and tailpipe coloration, but those are fairly vague and general. And that's why we suggest the best way to tune with the MAFtuner is on a dyno with a wideband oxygen sensor to precisely indicate real-time mixtures. As a starting point, you might confer with the support staff at Pro-M for suggestions on your particular vehicle.

By attaching a laptop, programmed voltage curves or meter calibrations can be downloaded to the MAFtuner's onboard EEPROM. The MAFtuner's existing voltage curves can also be uploaded and viewed-or modified-on the laptop. The voltage curves or "transfer functions" are simply voltage-in/voltage-out tables. Each row or data-point has the effect of saying, "For a voltage input of x.xxx received from the MAF, send a voltage output of y.yyy to the EEC." Among the various options, you can either directly edit the output voltages yourself in the main program window and then save the file to the EEPROM, or you can use the software's "Meter Matching Tool" files to specify the original mass air meter calibration and the desired calibration to be matched. The latter are available for a number of meter/injector combinations.

Finding Power on a Near-Stock GT
You'll have a field day when you strap a MAFtuner on a wildly modified blown application that idles like a pig and belches more black smoke than a pulling tractor at full throttle. Fixing those situations is right up the MAFtuner's alley. But we figured the toughest test for it would be on a near-stock vehicle, where the factory calibrations should be close to bang-on. We decided to test this theory on an '00 Mustang GT belonging to Brian Lamparski. Brian's red GT is-powerwise-stock except for a Bassani cat-equipped X-pipe (even the after-cat exhaust was OEM). We strapped it down on the Mustang MD-1750 chassis dyno at Detroit Speedworks, hooked up the shop's wide-band O2 sensor, and went hunting for horsepower. With the dyno loaded to reflect vehicle weight, a baseline pull netted 201.2 hp at 4,250 rpm and 252.8 lb-ft of torque at 4,000.

Pro-M's Scott Beer noticed that, between about 4,100 and 5,000 rpm, the air/fuel ratio seemed unreasonably rich, hovering at about 11.5:1, whereas a more desirable wide-open-throttle mixture for normally aspirated engines is generally in the area of 12.5:1. There was a clear dip in the horsepower and torque curves in this rev range. Taking advantage of the MD-1750 dyno's speed-hold function, whereby the car can be held, full throttle, at any desired speed, Scott was able to real-time adjust the mixture ratio closer to 12.5:1 using the MAFtuner's potentiometer knobs, while monitoring the results on the wide-band's display. The payoff was that peak horsepower jumped to 208.9 at 4,750 rpm, while torque was bumped to 255.2 lb-ft at 4,000 rpm. In this instance we gained nearly 8 peak horsepower and a couple lb-ft of torque on a near-stock modular. But we'll say it again: The mere act of "bolting on" a MAFtuner is not going to produce appreciable power gains (though the folks at Pro-M say its sample rate is so high that it does tend to act as a signal conditioner, smoothing out mass-air voltage oscillations that can cost a horsepower or two). It is, however, a powerful and precise tuning tool that, in the right hands, can potentially unlock hidden power or solve driveability issues related to air/fuel ratios.

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