Tuning FAQ

Note: This section has had very little in the way of contributions and is not, in its current form, anything close to a comprehensive tuning guide. The RomRaider forums contain the most up-to-date and useful tuning information.

1. Read the current ROM image from your car. RomRaider cannot actually help with this - this step requires EcuFlash. Also note that most cars must be put into ‘test mode’ for reading or writing.

1. Write your modified ROM image to your car. (Again, this step requires EcuFlash and most cars must be put into test mode.)

1. The “Learning View” utility (by merchgod) shows fuel trims and fine learning knock correction (and actually works just as well with the parked).

Q How do I tune my car?

Tuning is an iterative process.

1. Read the current ROM image from your car.
2. Learn about the car’s behavior with the current ROM image, using a logger or other data-collection tool to gather log information from your car as you drive.
   1. RomRaider’s logger will record arbitrary parameters in real time.
   2. RomRaider’s MAF scaling tab will plot your MAF sensor’s results and help you tune the scaling
   3. RomRaider’s injector scaling tab will plot your fuel injectors’ behavior and you adjust scaling at latency
   4. The “SawMill” utility (by natewaddoups) will display knock in different load/rpm cells
3. The “Learning View” utility (by merchgod) shows fuel trims and fine learning knock correction (and actually works just as well with the parked).
4. Look for problems such as knock, boost oscillations, boost that is lower or higher than desired, etc.
5. Consider opportunities to improve, such as timing that can be advanced, boost that can be increased, etc. This depends not only on your recent logs but also on your experiences with past logs.
6. Use RomRaider to edit your ROM image, making changes to address problems or opportunities that you’ve found.
7. Write your modified ROM image to your car.
8. Go back to the second step

If you are just starting out, you will want to:

• Read the RomRaider FAQ.

• Learn everything you can about tuning and logging. RomRaider’s tuning discussion forum is an excellent place to start.
• Read the following posts about ECU logic:
  • Subaru’s knock control strategy explained
  • Closed Loop to Open Loop fueling transition explained
  • Turbo dynamics and boost control explained
• Learn to use RomRaider to edit your ROM
• Learn to use EcuFlash to write your modified ROM to your car’s ECU.

This Tuning FAQ covers moderate to advanced topics. If you are just starting out, you will want to:

• Learn to use EcuFlash to read your ROM, so you can view it in RomRaider.
• Learn to use RomRaider to log data from your car.
• Learn everything you can about tuning. See the Articles section.
• Learn to use RomRaider to edit your ROM.
• Learn to use EcuFlash to write your modified ROM to your car’s ECU.

Be sure to visit the RomRaider FAQ for more basic questions about tuning and logging.

Airboy’s Excel Spreadsheet to import and graph log files is very useful for determining if/where timing is being pulled along with a number of other parameters.

Q I know relatively little about tuning and logging. Where should I start?

This Tuning FAQ covers moderate to advanced topics. Be sure to visit the RomRaider FAQ for more basic questions about tuning and logging.

• Something else to reduce the engine’s tendency to knock.

Q Why do the 32-bit ECUs have so many different timing and knock correction maps? How can I tell which one is being used and when?

Unfortunately, it isn’t quite fully understood when the ECU will decide to switch maps. Most people simply set all the maps to the same values so that the behavior of the car is consistent.

It is generally agreed that the stock KC map in conjunction with the IAM multiplier is used to smoothly adjust for varying levels of octane. This means that areas of the KC map with high values are more sensitive to knock than areas of the KC map with lower values. Areas of the KC map which are 0 when stock can be assumed to already be at MBT so there is generally no need to reduce timing in those areas.

For this reason, many people don’t completely flatten the KC map at all load/rpm cells, just the load/rpm cells where the stock map also has significant KC.

Q How can I tell if timing is being pulled due to knock?

You need to cross reference the RPM/load point and compare the logged timing and KC to the total timing and KC as calculated by the ECU. See earlier FAQ for determining total timing.

Q What should I do if timing is being pulled due to knock?

Short answer: Reduce the engine’s tendency to knock.

Long answer: One or more of the following:

• Reduce timing from the appropriate area of the base timing map
• Reduce timing from the appropriate area of the KC map
• Add fuel (richen the mixture) at the appropriate area of the fueling map
• Reduce boost (if other measures fail to eliminate knock)
• Something else to reduce the engine’s tendency to knock.

If the map’s scale isn’t large enough causing the lookup to go beyond the edge of the map, it will simply use the values of the cells on the edge of the map.

Q What is “flattening the KC map”? Why do people do it and how can I do it?

People often flatten the KC map to make it easy to tell whether the ECU is pulling timing due to knock or not when datalogging. For example, if your KC map is all one value, if you see a drop in KC, the ECU most likely is pulling timing in response to knock.

When flattening your own KC map, keep in mind that you will want to keep the total timing (Base timing + KC) the same. You should go through your KC map cell by cell, if you add 5 to a point of your KC map, subtract 5 from the corresponding point of your base timing map. Don’t forget to account for interpolation off the ends of the map as often the base timing and KC maps are not the same size.

Q Is there any drawback to flattening the KC map?

It is generally agreed that the KC map in conjunction with the IAM multiplier is used to smoothly adjust for varying levels of octane. This means that areas of the KC map with high values are more sensitive to knock than areas of the KC map with lower values.

This means that if you flatten the KC map, it is possible that timing may not be optimal if timing gets pulled because the IAM drops. For example, stock maps at low load usually have a KC of 0 meaning that the ECU will not adjust the total timing target at all based on the IAM. So if you flatten your KC map to all 10s and your IAM is half of what it could be, you will be running 5* less timing at light load where it really isn’t possible to knock therefore losing light throttle power and economy.

For this reason, many people don’t completely flatten the KC map at all load/rpm cells, just the load/rpm cells where the stock map also has significant KC.

• Knock sensors, KC, and IAM?

Q How does the ECU determine what value to use the maps? How does it interpolate?

The ECU will smoothly interpolate values as necessary between up to 4 cells (on a 2-axis map such as ignition timing) if necessary.

If the map’s scale isn’t large enough causing the lookup to go beyond the edge of the map, it will simply use the values of the cells on the edge of the map.

Q Why does my IAM drop when Knock Correction (KC?) is still positive?

Just because KC is positive does not mean that the ECU is not pulling timing in response to knock. Remember that if the logged KC value is less than (timing advance map value * IAM/16) for 16bit ECUs or (timing advance map value * IAM) for 32bit ECUs then the ECU? has removed timing advance from KC? due to what it perceives as knock.

If the IAM does drop, it is in direct response to the ECU? perceiving knock at that point in time. However the ECU? will only reevaluate IAM within the RPM and load ranges as specified by the ‘Rough Correction Range’ tables.

Q What determines total ignition timing?

KC? = (timing advance map value * IAM/16) + feedback correction + fine correction learning

For 32bit ECUs, use IAM in the calculation above instead of IAM/16.

Feedback correction is negative correction to KC? based on knock.

Fine correction learning is positive or negative correction to KC? for a given RPM and load range, based on knock or the lack of knock over a predetermined period of time. These corrections are stored in ram and are reevaluated within the RPM and load ranges specified by the ‘Fine Correction Range’ tables. In addition, the RPM and load ranges are determined by the ‘Fine Correction Rows’ and ‘Fine Correction Columns’ tables.

Other timing compensations include those calculated from coolant temperature and intake temperature, among others.

• Knock sensors, KC, and IAM?

“Fine correction learning” is positive or negative correction to KC? for a given cell in the RPM/load map, based on knock or the lack of knock over a predetermined period of time. Correction values are stored in ram.
“Other timing compensation” includes compensations calculated from coolant temperature and intake temperature.

See also:

• IAM, DA, and KC?
• Knock sensors, KC, and IAM?

KC? = (timing advance map value * IAM/16) + feedback correction + fine correction learning

“Feedback correction” is a negative correction to KC? based on knock.
“Fine correction learning” is positive or negative correction to KC? based on knock or the lack of knock over a predetermined period of time. Correction values are stored in ram.
“Other timing compensation” includes compensations calculated from coolant temperature and intake temperature.

\\ KC? = (timing advance map value * IAM/16) + feedback correction + fine correction learning

\\ “Feedback correction” is a negative correction to KC? based on knock. \\ “Fine correction learning” is positive or negative correction to KC? based on knock or the lack of knock over a predetermined period of time. Correction values are stored in ram. \\ “Other timing compensation” includes compensations calculated from coolant temperature and intake temperature.

\\KC? = (timing advance map value * IAM/16) + feedback correction + fine correction learning

\\”Feedback correction” is a negative correction to KC? based on knock. \\”Fine correction learning” is positive or negative correction to KC? based on knock or the lack of knock over a predetermined period of time. Correction values are stored in ram. \\”Other timing compensation” includes compensations calculated from coolant temperature and intake temperature.

Q What determines the total ignition timing?

Q Why does my IAM drop when KC? is still positive?

Just because KC is positive does not mean that the ECU is not pulling timing in response to knock. Remember that if at any time the logged KC value is less than Base Timing + IAM * KC? (divide IAM by 16 for 16-bit ECUs?) the ECU? has either seen knock at that load/rpm point before or just saw it.

If the IAM dropped that is in direct response to the ECU? seeing knock at that point in time. However, the ECU? doesn’t always reduce the IAM in response to knock. The ECU? only reduces the IAM while seeing knock in between certain RPM and load ranges (defined by your map). It tends to be the most aggressive in pulling IAM during moderate RPM/load situations.

Q What determines the total ignition timing?

Total Timing = Base Timing + KC? + other timing compensations KC? = (timing advance map value * IAM/16) + feedback correction + fine correction learning

For 32bit ecus, just use IAM in the calculation below instead of IAM/16. “Feedback correction” is a negative correction to KC? based on knock. “Fine correction learning” is positive or negative correction to KC? based on knock or the lack of knock over a predetermined period of time. Correction values are stored in ram. “Other timing compensation” includes compensations calculated from coolant temperature and intake temperature.

Q Why does my IAM drop when KC is still positive?

Just because KC is positive does not mean that the ECU is not pulling timing in response to knock. Remember that if at any time the logged KC value is less than Base Timing + IAM * KC (divide IAM by 16 for 16-bit ECUs) the ECU has either seen knock at that load/rpm point before or just saw it.

If the IAM dropped that is in direct response to the ECU seeing knock at that point in time.

Note that the ECU doesn’t always reduce the IAM in response to knock. The ECU only reduces the IAM while seeing knock in between certain RPM and load ranges (defined by your map). It tends to be the most aggressive in pulling IAM during moderate RPM/load situations.

Logging

Q What exactly is data logging and why is it important?

Logging allows you to monitor, real-time, a number of different data parameters used by the ECU in the management of the engine. This is important to track the impact that your tuning changes have on your motor. Logging is crucial to a safe and effective tune.

Q How does logging with RomRaider work?

RomRaider uses the Subaru Select Monitor (SSM) protocol for logging which is faster and has more capability than standard OBD-II logging. To use, simply connect the OpenPort cable to your OBD-II port and the laptop. Select “Launch Logger” from the Logger menu. Choose the correct COM port for your cable and RomRaider will auto connect to the ECU. Then you can select the parameters you wish to monitor as well the displayed format - data, graph or dashboard.

Q Can I log to a file?

Yes, select “Control File Logging with Defogger Switch” from the logger’s settings menu. To start logging to file, press the car’s defogger switch. To end logging to a file, press the defogger switch again. A new file will be created each time, allowing you to create separate files during each logging session. To change or view the location of the saved files, select “Log File Output Location” from the logger’s settings menu.

Q Which parameters should I log? Should I log everything?

Logging takes a snapshot of each parameter’s current value. The more parameters that are selected, the longer the interval between the sampling of each parameter. Therefore, you should limit logging to the minimum number of specific items that will supply you with the information you require. Try the following if you are new to logging: rpm, ignition timing, knock correction, manifold relative pressure (i.e. boost), primary wastegate duty, throttle opening angle %, A/F correction #1, A/F learning #1, mass air flow, engine load and IAM.

Q How can I view the saved log files?

Open them in any spreadsheet application that supports .csv files such as Microsoft Excel. Also check out Airboy’s spreadsheet to graph log files: http://www.romraider.com/forum/viewtopic.php?t=957

Q Do I have to connect the green test mode connectors or flash block to log?

No.

Q Why can’t Manifold Relative Pressure read over 18.4 psi?

This is a limitation of this parameter as set up by Subaru. Log “Manifold Relative Pressure (Corrected)” instead.

Q The logged advance multiplier (IAM) value is between 0 and 1 on some cars and between 0 and 16 on others. Why?

16-Bit and 32-bit ECUs store this value differently although the function of this parameter is the same. Multiply the 32-bit ECU’s value by 16 to compare to the 16-Bit ECU. Divide the 16-Bit ECU’s value by 16 to compare to the 32-bit ECU.

Q What is the difference between Engine Load (Calculated) and Engine Load (RAM)?

Engine load is not normally a parameter that can be logged through SSM. However, it can be calculated from the supported mass air flow and rpm parameters which is how “Engine Load (Calculated)” is determined. The “Engine Load (RAM)” reads engine load directly as calculated by the ECU and should be used if it is available for your rom.

Fundamentals

Getting Started

Q I know nothing about tuning. It is safe for me to experiment on my own car?

No. Changes that seem small and insignificant to someone who doesn’t know what they are doing can actually result in a blown motor or unpredictable behavior on the road. However, if you are willing to invest the time to learn the basics of tuning and engine management, then you can potentially tune with success.

Q Can’t I just download and flash one of the available staged maps such as those on osecuroms.org and not worry about tuning?

Yes and no. While these maps are designed for a particular model with specific mods, they cannot take into account the differences that may exist between individual vehicles, even those of the exact same model and year. These differences include the quality of the user’s gasoline, factory production tolerances, mechanical/maintenance issues, variances in the design and performance of aftermarket parts, additional mods outside the scope of map and varying extremes in which the vehicle will be driven such as altitude and temperature. This is true of any off-the-shelf (OTS) map, even those that are commercially available. It is important to at least understand the basics of how to log your car to determine if the map has any potential issues.

Q I’m not sure of the function of the some of tables that RomRaider lists for my rom. How can I found out more?

Each table has a basic description available by clicking on View → Table Properties on the table’s menu bar. For more detailed information about a specific table, search or ask about the table on the RomRaider site.

Yes, please see the Books? page.