MAF, which means Mass Air Flow, is a sensor that is positioned directly after the air filter and is designed to measure the mass of air crossing across an element inside the housing (in Grams per second). The ECU can then interpret these values and calculate the fuelling needed for the combustion cycle to be competeted efficiently and produce the desired AFR. Air density can change vastly with differences in temperature and pressure, so a airflow sensor works in conjunction with Lambda sensors and the intake air temperature sensor to ensure that the fuelling is precisely controlled to the demand of the engine.
There are two types of MAF sensor that are used in a 1.8T application and this depends on what type of ECU you use. The two types are Narrowband and Wideband. These can be identified by removing the sensor from the housing and noting three numbers printed onto the actual sensor. 040 identifies a Narrowband sensor. 049 identifies a Wideband sensor. These work in conjuction with the type of Lambda sensor too. So if you have a Narrowband MAF sensor, you will have a Narrowband Lambda sensor. The opposite applies for Wideband.
With the newer 1.8Ts, running a ME7.5 ECU, which are found from 2001 onwards; all of the actual sensor elements are identical (providing they are narrow or Wideband). So, a common misconception is the MAF sensors differ between 150bhp engines and 225bhp engines, whereas actually, its just the actual housing and scaling inside of the ECU maps that differs.
A common upgrade when chasing more power, is to change the MAF sensor housing for a larger diameter, which will allow the ECU to correctly see how much air is entering the engine and fuel appropriately for it.
Vr6 upgrade for the me3.8
Me7.1 is narrowband
Me7.5 is wideband
As you increase power, you naturally create more airflow. MAF housings work on a scale that calculates the airflow in g/s passing over the sensor. Once the reading reaches the max of the scale, it cant read any further. This is down to the diameter of the housing the MAF sensor sits in. A larger housing can allow more air to flow over it. If you have reached the maximum capacity of the housing, you can add a larger housing and scale it in via the ECU mapping done by your tuner. This allows more air to be accurately calculated allowing fuelling to be accurate aswell. A common upgrade is the S3 BAM housing which is 3″ in diameter. It is important to retain the square mesh lamier flow straightener as this stops erratic results the sensor picks up.
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