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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