5.0 Mustang & Super FordsHow To Engine
Pro-M MAFtuner: Air Fuel Mix Master
Optimizing your air/fuel ratio with Pro-M's MAFtuner
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.
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.
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.