This page provides an overview of topics for those interested in tuning their own Subaru or having it tuned professionally. See our gadgetry and software page for more information about the tools used and the electrical and control systems page, note that open source tuning depends on RomRaider and ECUFlash. We provide links to other sites and disclaim any damage caused by experimentation, always do your own research before making any changes to your car and operate within national and local regulations.
- Pay a professional tuner to tune your car on a dyno
- Pay a tuner to e-tune your car. This involves you sending the tuner log files and the tuner sending ROM's that you flash into your car, collect more log file drive data to send back to the tuner who makes adjustments to the ROM.
- DIY tuning. Make your own changes to the ROM in your car to adjust from collecting log file drive data.
- Chip tuning. Purchase a per-configured ROM to flash into your car. This is a blanket approach that doesn't take into account that all engines have slightly different characteristics.
- Pedal tuning. A physical device that intercepts accelerator pedal position to magnify the value sent the the engine computer for better response.
If you want to tune your car or understand terms such as IAM, FBKC, FLKC, etc… be sure to read these documents, these are not optional reading!
¶ ECU Parameters and Tables
The terminology can be confusing at first.
- ECU - engine control unit - most 2005-2009 Subaru ECU's are modifiable to to some extent
- TCU - transmission control unit - not directly modifiable
- Standard Parameter - a value in the ECU that is made available to OBD-II and other diagnostic equipment through the OBD-II channel
- Extended Parameter - a value that the ECU uses for it's own calculations. These are only available to end users once the ROM address has been reverse engineered.
- Constants - single value
- 2D table - X,Y values - i.e. scaling values to calculate Mass Air Flow g/s (Y) from voltage (X)
- 3D table - X,Y,Z values - i.e. ignition timing values (Z) from Engine Load (X) and Engine Speed (Y)
You can find more information about the parameters where you install RomRaider as one step in the install process is to configure a logging definitions file that contains all parameters.
IAM (ignition advance multiplier) is a often discussion topic as it controls how much timing advance is applied, hence an indicator of timing health. On 32-bit ECU's the value should be 1.0 unless ECU was reset by software or a battery disconnect in which case IAM will take a few kilometers of driving to relearn. There are a values of IAM to be aware of.
- IAM at 1.0 - the tuning is generally healthy
- IAM at 0.5 - this is usually the initial value after reset
- IAM at 0.0 - the ECU is still learning, it doesn't have enough info to provide a value
This is a very high level view, see the tuning guides on this page and read the Subaru knock control strategy document.