General Information on Mass Air Meters (1988-2010)
One of the real problems you might face when you start making more power with your vehicle is you might just "peg" your mass airflow sensor (MAF). What is pegging? When you peg your MAF, you have not reached the airflow limit of the MAF - MAFs, even smaller sized ones, will flow enormous amounts of air. Pegging refers to hitting the electronic capacity of the sensor.
MAFs use a tiny heated wire in the airflow stream and a thermistor - which is a resistor that varies resistance according to temperature. The ECU keeps scaling voltage up to keep the temperature of the wire the same, but as airflow increases, the wire keeps getting cooler and cooler, and the ECU increases current to keep the temp the same. The current flow is measured and a voltage signal is sent back to the ECU and the ECU uses this to measure the mass or weight of the incoming air. It's a little more complicated than that, but that's basically how it works.
On Ford MAFs, some of which are manufactured by Hitachi, the MAF will output voltage to battery voltage. However, the ECU is set up to only acknowledge a maximum of about 4.7 volts. This is without a tune. . After the MAF gets past the maximum limit that the ECU can use, bad things start happening.
Bad thing #1 - The ECU controls injector pulsewidth based on the data it is receiving from the MAF signal. It tries to maintain the commanded air to fuel ratio in the base fuel table. For a naturally aspirated engine at wide open throttle, this is usually around Lambda 0.85. On a blower or turbo motor, this is Lambda 0.77-0.80 depending on a number of variables. Once the voltage limit is attained, the ECU 'thinks' that there is no more air coming into the engine so it does not increase fuel flow. But there is an ever increasing airflow - so what happens is the engine goes lean very quickly. The end result is burned pistons, valves, detonation, blown head gaskets... you get the picture, the bottom line is you better be in a spending mood, because you'll need a new engine. This is especially bad with a blower or turbo motor.
Bad Thing #2 - The MAF does another key function for engine control. It supplies data to the ECU so the ECU can calculate "load". Load is similar to volumetric efficiency, it is a measure of the engine's capacity to fill each cylinder with air/fuel. What's important is that load is used by the ECU for a number of things, two of the things might be timing and fueling. Generally at low loads, timing is much higher and fueling is much leaner than at higher loads. When the MAF pegs however, the load measurement starts drifting down. So timing goes up and fuel goes even leaner.
Bad Thing #1 + Bad Thing #2 = BOOOM!!
Usually on a stock 1989-2004 GT, the MAF is good to around 300 RWHP - some will peg sooner, some later. 80mm Lightning MAFs add a little to that, about 350-375 RWHP, while 90mm Lightning MAFs will peg at about 450 RWHP. SCT BA 2400/2600 MAFs are good to around 625 RWHP and the BA 2800/3000 are good to near 700 RWHP or so. Any of the SCT MAFs will give almost stock drivability, but they need a tune to work properly. Most people skip the 80mm Lightning MAF and go right to the 90mm unit.
Any Ford MAF as well as the SCT MAFs are NOT calibrated for any injector size. The injector size is set in the ECU. We do NOT recommend MAFs that are 'calibrated' to injector size mainly because the calibration is usually not correct and the curve is out of line. These types of MAFs also skew load calculations throwing timing calculations off. We CAN work with these types of MAFs, but driveability will usually never be as good as stock.
1996-2004 model cars have the right connector and usually only need a filter adapter, a 4" cone filter and a silicon adapter to adapt the MAF to the powerpipe. Earlier model cars need a pigtail harness. Late Model cars incorporate the ACT (temp sensor) in the MAF - all SCT MAFs have the temp sensor included. The two outer wires are for the temp sensor and are not used by earlier models using and external sensor.
Please use any information gathered here at your own risk.