AF = Mass Air Sensor Flow (MAF)
As stated at the beginning of this section, our cars come from the factory with a mass air form of fuel injection control which uses a flow meter, that we refer to as a mass air sensor, to measure the mass of the air flowing into the engine. Note that it measures mass and not volume. Hot air is less dense than cold air and thereby has less air molecules in a given volume than does the cold. Given that it is the number of air molecules in the cylinder that must be matched with fuel, it is important to know the mass.
The original factory mass air sensor is/was capable of measuring mass air flow from 3 to 150 grams per second. This is displayed on the scan tool over a range of some 3 to 255. 255 is numerical limit of the 8 bit processor in the ECM. The later LT-1/LS-1 mafs that can be used with
Bob Bailey's Translator system can potentially flow a higher mass of air than the original units if the engine can use it.
This parameter is a big help in troubleshooting. One of the first suspects when the car is not idling/running correctly is often the MAF. This is particularly true if the original style MAF is being used. To verify operation, turn the key on, but do not start the engine. The AF on the scan tool will normally read 3. Then, start the engine. With a normal idle speed, it will normally read 4-6, and, may read 7 if the programmed idle is around 800/850 rpm as the faster idle will require more air thru the sensor. If the MAF is reading in this range, one can be pretty sure that it is not the problem that is causing the car to not run properly...particularly at idle.
Now, the MAF can also lose calibration at higher mass flows. As stated prior, 255 is the maximum number that can be displayed. Cars running boosts close to 15 psi or so may report less than 255..say 245, or thereabouts. As the boost gets closer to ~17 psi, the car will normally begin to max the reading out and one would expect to see 255, or very close. Design of the intake tract, engine size/combination, etc. will affect the actual number.
If one has been seeing 255 and then it starts reading 235, one may start having problems as one transitions to wide open throttle as the ECM believes the car is consuming less air and therefore provides less fuel.
If one has a logging scan tool such as PowerLogger, then the graph of the MAF output should be smooth with no spikes, or, sudden dips on a wide open throttle run.
The later style MAF/Translator systems are generally far more robust and don't cause many problems as long as the wiring is solid on the install
"AF" of the Scanmaster. This is from Vortexbuicks.com
