The MAF meter
The MAF is a "mass" air meter. What this means is that it reads the MASS of the air entering the motor. This concept is very important in that air mass is the final value the tuner is looking for when adjusting the tune. All fueling calculations are based on air MASS. The MAF is the most accurate sensor when it comes to determining air mass, and thus all fueling calculations.

Now, one might think that if the MAF is the most important accurate component in reading air mass for fueling calculations, that it would be all we need for accurate fueling. But the MAF does have its limitations. First off, this is a steady state sensor. What that means is the sensor does not respond well to sudden changes in airflow. The MAF is most in its element at WOT above 4000rpm's. Under this condition the computer will actually disregard all other input in favor of the MAF. But where the MAF fails in under light airflow, and transient conditions. This is when you mat the pedal, or during light cruise. This is when the MAf becomes lazy and can't read effectively. Under these conditions the VE becomes important. But this will be discussed the VE and SD threads.

Now, how does one tune the MAF? If it is so accurate, and pumps out mass flow numbers, then why is there a need to modify the table?
Well, some of the time, there is no need to modify it. But anytime there is a change in the inlet tubing, or air filter assembly, then the MAF should be checked. Now here is the kicker! Since the MAF is a steady state device, how do you check it on a car that will almost never enter steady state (espescially at WOT).
The new concept is to test and tune the meter on a flow bench. With a flow bench the tuner can adjust airflow for every frequency encountered by the meter. This will allow the tuner to stabilize flow and verify MAF output. If needed, then a new MAF transfer function can be modeled and input to the new tune.
The other reason for checking the MAF is to adjust the factory variances inherant in mass production parts, and tune the specific output so the metered vs actual calculations have a less than 1% error.

Thanks for posting this info up Mike...makes me glad people like you are available to tune my goat. This kind of stuff makes me miss the good ole days when I cold tune a car with a screwdriver, a socket and timing light! LOL

Well, I want people to be informed on what is being changed on their car, and how it effects how it runs. In informed consumer is generally a good thing.

I also want to create a question and answer section to further enhance peoples understanding of fuel injection.