The boys over on the opensource forums have finally licked this and created a way for anyone to custom tune their car for the intake/fuel resonance that exists in the GR engine. The symptoms are slight but tremendously annoying hesitations/surging in acceleration under light load (0 boost and lower) that occur between 2400 and 3000 rpm.
The reference thread is here:
RomRaider • View topic - How to fix the GR STi 2400-3200 stumbles
You need a recent version of Cobb's accessTuner Race, an AP2 and Engine Compensation spreadsheet that can be downloaded here:
RomRaider • View topic - Spreadsheet to generate fuel trim pivot table (RPM v. MRP)
I would recommend reading this thread as well.
I'm not going to hold anyone's hand and write an exact tutorial on what to do - I believe you should not be changing things in ATR if you don't understand what you are doing. But I will provide an overview.
Open the spreadsheet in the form that you download it. The main table will show you the data from another user. The header columns are the things you need to log with your AP. The only wrinkle is that RomRaider and Cobb call the same data different things - manifold relative pressure is boost in cobb lingo, A/F correction #1 is fuel trim (short) in Cobb, A/F learning #1 is fuel trim (long) in Cobb. The rest are straightforward.
Drive on the highway for between 30 minutes to 2 hours logging the required data. Try and keep the throttle relatively constant for minutes at a time and drive across the whole rpm range that you need data for - you will be driving from 60 to 75 mph. If your highway has long slight hills even better.
Open your log in Excel and rename your headers to match the headers in the spreadsheet (they don't have to be in the same order, but I usually rearrange them because I'm anal). Once you've done that save the file, use the spreadshreet and click on 'get data'. It will ask you where the file is. Once it has your data, click on 'Filter'. The spreadsheet generates a pivot table of RPM vs manifold pressure, showing fuel correction needed at each cell point in the table. This is the data you are going to use to adjust your Calc. Engine Load Compensation B table under Sensor Calibrations in AccessTuner. The labels in the spreadsheet for pressure are in boost, the labels in ATR are in boost/14.7, but the columns correspond exactly with those in ATR. Any cell that has sufficient data will be black, cells with not enough data will be empty or grey. Add the value of the cells in the pivot table to what is in the Engine Load table.
To generate the values for Compensation A, you need to click on the ROM tab in the spreadsheet and change the RPMs that the pivot table uses (Compensation A has additional RPM values at 2700 and 2750). Once you change the values in the ROM table, 'Filter data' again and you will get a new pivot table.
The spreadsheet will also generate some nice 3D graphs. In my case it was blatantly obvious what was causing my stumbles. The short term trim was adding over 25% more fuel at 2400 rpm and light load and removing 15% at 2800 rpm at slightly higher load. After adding the pivot values to my compensation tables and relogging all my trim values are less than 5% and I don't get ANY knock at cruising anymore.
If I'm not clear on something let me know.
The reference thread is here:
RomRaider • View topic - How to fix the GR STi 2400-3200 stumbles
You need a recent version of Cobb's accessTuner Race, an AP2 and Engine Compensation spreadsheet that can be downloaded here:
RomRaider • View topic - Spreadsheet to generate fuel trim pivot table (RPM v. MRP)
I would recommend reading this thread as well.
I'm not going to hold anyone's hand and write an exact tutorial on what to do - I believe you should not be changing things in ATR if you don't understand what you are doing. But I will provide an overview.
Open the spreadsheet in the form that you download it. The main table will show you the data from another user. The header columns are the things you need to log with your AP. The only wrinkle is that RomRaider and Cobb call the same data different things - manifold relative pressure is boost in cobb lingo, A/F correction #1 is fuel trim (short) in Cobb, A/F learning #1 is fuel trim (long) in Cobb. The rest are straightforward.
Drive on the highway for between 30 minutes to 2 hours logging the required data. Try and keep the throttle relatively constant for minutes at a time and drive across the whole rpm range that you need data for - you will be driving from 60 to 75 mph. If your highway has long slight hills even better.
Open your log in Excel and rename your headers to match the headers in the spreadsheet (they don't have to be in the same order, but I usually rearrange them because I'm anal). Once you've done that save the file, use the spreadshreet and click on 'get data'. It will ask you where the file is. Once it has your data, click on 'Filter'. The spreadsheet generates a pivot table of RPM vs manifold pressure, showing fuel correction needed at each cell point in the table. This is the data you are going to use to adjust your Calc. Engine Load Compensation B table under Sensor Calibrations in AccessTuner. The labels in the spreadsheet for pressure are in boost, the labels in ATR are in boost/14.7, but the columns correspond exactly with those in ATR. Any cell that has sufficient data will be black, cells with not enough data will be empty or grey. Add the value of the cells in the pivot table to what is in the Engine Load table.
To generate the values for Compensation A, you need to click on the ROM tab in the spreadsheet and change the RPMs that the pivot table uses (Compensation A has additional RPM values at 2700 and 2750). Once you change the values in the ROM table, 'Filter data' again and you will get a new pivot table.
The spreadsheet will also generate some nice 3D graphs. In my case it was blatantly obvious what was causing my stumbles. The short term trim was adding over 25% more fuel at 2400 rpm and light load and removing 15% at 2800 rpm at slightly higher load. After adding the pivot values to my compensation tables and relogging all my trim values are less than 5% and I don't get ANY knock at cruising anymore.
If I'm not clear on something let me know.
