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The Basics

What you will need

  • Tactrix OpenPort - Tactrix makes a product called an OpenPort that lets you upload and download tuning information using a laptop. The original OpenPort (versions 1.0 - 1.3) was a cable with a USB connector at one and and an OBD2 connector at the other end. The current OpenPort (version 2.0) is a little box that plugs into the OBD2 port and you plug a USB cable into it… but everybody still calls it a “Tactrix cable” anyway.
  • EcuFlash is free software that uses the OpenPort to actually copy a tune to and from the car (copying a tune to the car is called reflashing). EcuFlash will also let you edit the tables in the tune.
  • RomRaider is free software that also lets you edit the tables in the tune. RomRaider is also a logger - it uses the OpenPort to connect to the car and record parameters from the engine to a file on your laptop. Logging is how you find out if your tune is working well or not.
  • Learning View is free software that shows the information that your ECU learns as you drive. Currently there are three kinds of learned information:

1) AF Learning A, B, C, D, also known as “fuel trims.” These indicate whether your MAF scaling is correct or not. For information about these values, see here.

2) Knock Correction. There is the Ignition Advance Multipler (IAM) and there’s a table of learned knock corrections and different RPM and airflow (load) cells. For information about these values, see here.

3) Diagnostic Trouble Codes, or DTCs. If present, these indicate problems with your car. For more information about these codes, enter the code number (e.g. “P0420”) into the search engine of your choice, and see what comes up.

Preparing to Tune

Is your car healthy?

You’ll generally start by logging to make sure that (or find out if) the car is healthy. First, just do some mild freeway driving, and use Learning View to make sure that your fuel trims are all in the range of −5% to +5%. If they are not, stop here and work on MAF Scaling.

If your fuel trims are all reasonable, you may start do log some pulls. A “pull” means going from 2000–2500 RPM to redline. Find a safe place for this. For most of us, that means going far outside of populated areas, preferably to an interstate freeway onramp that will allow you to reach redline in 3rd gear, then slow down a bit before the ramp merges with the freeway.

Start by logging a pull at half-throttle. Then stop the car and examine the log. Log examination is beyond the scope of this introduction, but essentially you want to look for knock, look at your boost level, and look at your AFR. If the car is not knocking and if nothing weird is happening to the boost and AFR, repeat the process, adding a bit more fuel each time, until you are pulling at wide open throttle (WOT) from 2500 to redline.

Most of us prefer to look at logs using Excel, as it makes it much easier to visualize the information in the logs. If you don’t know how to use Excel, this is an excellent time to learn.

Is there room to make more power?

How much power your car can make is beyond the scope of this article, but it helps to look at what boost, AFR, and timing other people are making this similar cars and similar modifications. Generally speaking, you make more power by adding boost, adding timing, and perhaps by leaning out the mixture (Subaru’s factory tunes run quite rich). However, if you get too greedy with any of those, the engine will knock, and knock will eventually destroy your engine.

The Tuning Workflow

  1. Decide what you want to accomplish. More boost? More timing? Leaner mixtures? Tune out boost spikes?
  2. Choose a set of parameters that will show you what you need to know to accomplish your goal. Decide what boost and AFR and timing you thing are reasonable.
  3. Log the car to create the conditions you are interested in. When tuning for power, this usually means WOT pulls, but part-throttle pulls and low-boost pulls are also useful to get smooth driveability.
  4. Study the logs. Look for detonation. Look for deviations between the actual boost, AFR, and timing, an the numbers that you want or expect.
  5. Revise the appropriate tables in the tune.
  6. Flash the revised MAP to the ECU.
  7. Go back the step 1.


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Page last modified on September 29, 2009, at 02:40 AM
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