How does the AFC / S-AFC work?

The AFC works by changing the mass airflow sensor (MAS) signal going into the ECU. This signal is a frequency proportional to the amount of air passing through the sensor.

Picky tech-heads will realize that the MAS puts out three signals: air flow, air pressure, and air temperature. The ECU integrates all of these to calculate air mass. The AFC alters only the air flow signal.

Different levels of adjustment to the signal occur for the different RPM ranges. In-between ranges, the AFC uses linear interpolation to smoothly transition from one adjustment level to the next. Thus, if the AFC is set to +10 at 2000 RPM, and - 10 at 3000 RPM, the signal correction at 2500 RPM will be zero.

The Super AFC also has two different correction maps based on throttle position. The "Th" (throttle) points set inside the unit by the user determines the low-throttle and high-throttle boundaries. The AFC also interpolates between the low and high settings at part throttle. Thus, if the low throttle is set at 10% and has +10% correction, and the high throttle is set at 90% and has +20% correction, the correction at 50% throttle will be +15%.

Despite this flexibility the AFC suffers a few drawbacks. It does not "know" the engine load, only engine RPM. For this reason it is hard to tune each gear ideally, since the engine load at any RPM in 1st gear is different than that in 3rd or 5th gear.

AFC owners should check out the Super-AFC-DSM mailing list on Yahoo! Groups. You need a Yahoo! ID since membership is now restricted. To join, click here.