Subaru AcccessTUNER Software
Subaru AcccessTUNER Software
Subaru AcccessTUNER Software USDM 2.5L Speed Density Guide Version 1.1 Prepared by: COBB Tuning Calibration and Engineering Teams Documents Available: USDM 2.5L ECU Software Change Guide USDM 2.0L ECU Software Change Guide USDM 2.5L Speed Density Guide USDM Subaru Monitor Descriptions USDM Subaru Table Descriptions
Table of Contents Overview . . 5 Uses . . 5 Supported Vehicles List . . 5 Glossary of Acronyms . . 5 Features . . 6 Hardware Requirements . . 7 Warnings . . 8 OFF-ROAD USE ONLY . . 8 READ ALL DOCUMENTATION BEFORE TUNING . . 8 SD IS NOT FOR INEXPERIENCED SUBARU TUNERS .
. 8 VERIFY FACTORY AIRFLOW AND LOAD LIMITS AND RAISE AS NEEDED . . 8 MANIFOLD PRESSURE SENSOR CHECK ENGINE LIGHT ERRATIC LOAD CALCULATION . . 8 ENGINE HARDWARE CHANGES MAY REQUIRE A RE-TUNE FOR SD . . 9 POTENTIAL RISKS FOR SD WITH A HEAT SOAKED IAT SENSOR . . 9 SD Installation Steps . . 10 What is Speed Density . . 11 What is Volumetric Efficiency . . 11 Volumetric Efficiency Table . . 11 SD Modes . . 12 Tuning SD – Mechanical Configuration . . 13 Tuning SD – Getting Started . . 13 Tuning SD – Initial Map Configuration . . 13 Airflow and Load Limits . . 13 Manifold Pressure Sensor Diagnostic Trouble Codes .
. 13 Load and MAF Compensation . . 14 Conservative Fuel and Timing Maps . . 15 Injector Scaler and Latency . . 15 Engine Displacement . . 15 VE Table Axis Scaling . . 15 Reflash Changes . . 16 Tuning SD – Starting Values for the VE Table . . 16 Copyright © 2012 CobbTuning Products, LLC. All Rights Reserved Page 2
Car with Working and Accurate MAF Sensor . . 16 Car without Viable MAF Sensor Configuration . . 17 Tuning SD – The Tables . . 18 “SD Volumetric Efficiency” Table . . 18 “SD Airflow Compensation (Intake Temp)” Table . . 19 “SD Airflow Compensation (Coolant Temp)” Table . . 21 “SD Airflow Compensation (Barometric)” Table . . 21 Tuning SD – Miscellaneous Tables . . 21 Load Filtering in MAF and SD Mode . . 22 Map Determination Averaging Window . . 22 SD Feature Activation . . 23 Tuning SD – Post-Tune Recommendations . . 23 Tuning SD – Additional Topics . . 24 Recommended Calibrations for Aftermarket IAT Sensors .
. 24 . . 24 Recommended Calibrations for Aftermarket MAP Sensors . . 24 Forcing Open Loop Fueling . . 25 Long-Term Fuel Trims . . 25 Removing Influence of Rear Oxygen Sensor on Fueling . . 26 Cam Timing (AVCS) Tuning Changes and Effect on VE . . 27 Tuning MAF Mode . . 27 Tuning Hybrid Mode . . 27 Overview . . 27 Hybrid Mode - Uses . . 28 Hybrid Lower/Upper Mode . . 28 Hybrid Threshold Switching Behavior . . 28 Hybrid Thresholds Overview . . 29 Hybrid Threshold Individual Deactivation . . 29 Hybrid Transition Blending . . 29 Tuning Hybrid Mode – Post-Tune Recommendations . . 30 How to Monitor the Tune .
. 31 SD Real-Time Tuning . . 34 Row/Column Table Data and Dynamic Advance Tables Removed from Real-Time . . 34 Copyright © 2012 CobbTuning Products, LLC. All Rights Reserved Page 3
Other Changes to Real-Time . . 34 Real-Time Tunable SD Tables . . 34 SD Airflow Math . . 35 Ideal Gas Law – Introduction . . 35 Ideal Gas Law – Real-World Inputs . . 35 Ideal Gas Law – Volumetric Efficiency . . 36 Ideal Gas Law – Mass Airflow . . 36 Ideal Gas Law – SD Reference Airflow . . 36 SD Final Airflow . . 37 Estimated VE Calculation . . 38 Appendix – Aftermarket IAT Sensor Install . . 40 Copyright © 2012 CobbTuning Products, LLC. All Rights Reserved Page 4
INTRODUCTION Overview The COBB Speed Density feature is a powerful yet easy-to-use solution that integrates Speed Density tuning into the Subaru engine control unit (ECU) and can be used to entirely replace or work in conjunction with the existing factory mass airflow (MAF) sensor.
It is highly customizable and features such as real-time tuning aid in a speedy and efficient tuning process. Uses COBB Speed Density (SD) has a number of potential uses that can improve the tuning capability for particular set-ups: • SD can eliminate the noisy airflow calculation sometimes seen when using a MAF sensor-based configuration with heavily modified cars.
• SD allows for the MAF sensor to be removed, eliminating a potential restriction in the intake tract and allowing for more freedom in intake piping design. • In a special hybrid mode, SD can be used on the high end to overcome a maxed out MAF sensor, while still retaining MAF sensor operation on the low end. Or SD can be used on the low end to improve idle/cruise characteristics when a big MAF is used, while still retaining MAF sensor operation on the high end. Supported Vehicles List The following vehicles designed for and sold in North America are supported: • 2006-2012 Subaru Impreza WRX • 2004-2012 Subaru Impreza STI • 2009 Subaru Impreza 2.5GT • 2004 - 2012 Subaru Forester XT • 2005-2012 Subaru Legacy GT • 2005-2009 Subaru Outback XT Glossary of Acronyms • ECT = Engine Coolant Temperature • ECU = Engine Control Unit • IAT = Intake Air Temperature Copyright © 2012 CobbTuning Products, LLC.
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• IC = Intercooler • MAF = Mass Airflow • MAP = Manifold Absolute Pressure • RPM = Revolutions Per Minute (referring to engine speed) • SD = Speed Density • VE = Volumetric Efficiency • WBO2 Sensor = Wideband Oxygen Sensor Features The following is a list of the key features of COBB Speed Density (SD): • SD works by calculating a new SD-based airflow to replace the factory MAF sensor-based airflow when SD is active. This keeps much of the existing factory logic in place, allowing for the safe and reliable operation of the factory ECU while reducing the learning curve associated with tuning SD.
• Adding the SD functionality to your existing COBB maps is a simple as opening the map in the AccessTUNER software with the SD ECU selected, saving the map, transferring the map to the AccessPORT, and reflashing the map to the car. From there, you simply start tuning with the AccessTUNER software. • Tuning SD is achieved through manipulating a real-time tunable volumetric efficiency (VE) table. Because the VE table units represent actual VE, properly calibrated SD tunes can be used to compare VE across different cars with different mods, even if the SD airflow is drastically different.
• A real-time tunable intake air temperature (IAT) compensation table allows the tuner to tweak the SD charge temperature correction.
This table can be tweaked according to manifold pressure, allowing for changes that may be needed based on IAT sensor placement. SD airflow compensations for engine coolant temp (ECT) and barometric pressure are also available. • Tuners can select from three different real-time tunable modes of operation. MAF mode mimics the factory logic in which airflow is determined by the MAF sensor and the“MAF Calibration”table. This mode allows you to get a starting VE table up and running before actually running SD or allows you to tune MAF sensor calibration as you would with the factory ECU. SD mode is full-time SD operation where the ECU uses the SD- based airflow calculation.
Hybrid mode allows for switching between MAF and SD mode (and vice versa) based on thresholds of throttle, RPM, MAP and MAF voltage. During the transition, the MAF sensor and SD- based airflow calculations will be blended over a short period of time to allow for a smooth transition between modes. The speed of this transition and how the switching takes place can also be configured. • The SD and MAF sensor-based calculations are made regardless of mode. This means that the MAF sensor- based airflow can be compared to SD airflow regardless of which airflow value is currently being used. Copyright © 2012 CobbTuning Products, LLC.
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• For cars with a properly calibrated and installed MAF sensor, an available estimated VE monitor can be used to more quickly get the initial tune for the VE table up and running. This can even be done in MAF mode, where the VE table (and other SD elements) can still be tuned before actually running SD. • Because the response characteristics of the MAF sensor (used in MAF mode) and the MAP sensor (used in SD mode) are different, a tunable load smoothing factor is available for each mode. This determines how load is filtered by the ECU and allows for better idle and tip-in/tip-out behavior in SD mode, while retaining the correct filtering in MAF mode.
Hardware Requirements The following minimum hardware requirements must be met in order to use the SD feature: • MAP Sensor - The manifold absolute pressure (MAP) sensor installed in the car must be accurate, reliable, and capable of reading boost greater than the car can ever achieve. A typical car that would necessitate an SD tune would likely max out the factory MAP sensor and require an aftermarket MAP sensor to be installed. Any aftermarket MAP sensor must be properly scaled in the map (via“MAP Sensor Calibration (Offset)”and“MAP Sensor Calibration (Multiplier)”tables) and its accuracy should be verified by an external boost gauge before tuning SD.
Note: A MAP sensor related check engine light can cause a failsafe load calculation to come into play, potentially causing issues when SD mode is active (please see“Tuning SD – Initial Map Configuration” section for more details).
• IAT Sensor - Vehicle must have a working, accurate and properly calibrated intake air temperature (IAT) sensor. The IAT sensor is crucial to the SD airflow calculation. The SD airflow calculation relies on a theoretical input of the cylinder charge temperature. The closer the IAT reading is to the actual cylinder charge temperature, the more accurate (and consistent) the SD airflow calculation will be and the easier SD will be to tune. The factory IAT sensor is in the MAF sensor assembly in a draw-through configuration (i.e. pre-turbo). While it is possible to tune SD with an IAT sensor in this location, it is more difficult and will require more tweaking of the SD IAT compensation table (because this placement does not take into consideration turbo and intercooler efficiency).
We recommend that the IAT sensor be placed post-intercooler, if possible. This could be using the factory MAF/IAT sensor assembly moved to a blow-through configuration (i.e. post-front mount intercooler) or an aftermarket IAT sensor placed in the intake piping in the same location (see appendix for details on how to install an aftermarket IAT sensor). Keep in mind that an aftermarket IAT sensor will require a different calibration that the factory IAT sensor.
• Other Sensors – Any sensor or component necessary for the operation of the factory ECU must be working, installed, and properly calibrated. The only exception is the MAF sensor assembly if the tune is set to run only in full-time SD mode (see“MAF Sensor Removal”below). • MAF Sensor – The MAF sensor assembly must be installed and properly calibrated if the MAF mode, hybrid mode, or estimated VE monitor is to be used. It must also be installed if the factory IAT sensor (which is part of the MAF sensor assembly) is to be used for SD (rather than an aftermarket IAT sensor). • MAF Sensor Removal – If the MAF sensor is removed, disconnected, or otherwise non-functional, you will only be able to run the car in full-time SD mode and the car will not start or run when MAF mode is active.
You will also need to disable any MAF sensor related diagnostic trouble codes (DTCs) such as P0101, P0102, and Copyright © 2012 CobbTuning Products, LLC. All Rights Reserved Page 7
P0103. While the ECU’s primitive failsafe load calculation has been disabled in the COBB SD ECU, disabling the MAF sensor DTCs is still necessary because other fail-safe logic can come into play. Also, removal of the factory MAF sensor assembly also removes the factory IAT sensor requiring you to install an aftermarket IAT sensor. • Wideband Oxygen Sensor – A properly functioning and installed wideband o2 (wbo2) sensor is necessary to tune SD. It is also highly recommended that a permanently installed wbo2 sensor with an interior gauge is used so that the driver can monitor fueling after the tune is complete.
• Mechanical Issues - Any mechanical problem with the car needs to be addressed before attempting to tune SD. Warnings OFF-ROAD USE ONLY Some or all of the features and modifications discussed in this guide may not be legal to use outside of off-road racing applications. Always consult local, state and federal laws to determine what is legal for your particular situation. READ ALL DOCUMENTATION BEFORE TUNING COBB SD for Subarus has been designed with the purpose of coming up with the best implementation for the unique attributes of the Subaru ECU, while allowing for an easy conversion to SD for existing MAF sensor-only maps.
COBB SD is not like other SD systems that you may be familiar with, including even COBB implementations for other platforms. As such, it is critical that you read through this guide and understand how COBB SD for Subarus works before attempting to tune. If you have any questions, we are always willing to help. SD IS NOT FOR INEXPERIENCED SUBARU TUNERS There are many unique qualities to Subaru ECU logic that can make it challenging for someone new to the platform. If you are new to Subaru tuning, it is recommended that you first become proficient at tuning MAF sensor-only set-ups before tackling SD tunes.
MAF sensor-only tuning can be much more forgiving to mistakes than SD tuning. VERIFY FACTORY AIRFLOW AND LOAD LIMITS AND RAISE AS NEEDED It is important to understand that the factory airflow and load limits are still applied even when the SD-based airflow is being used. Please see“Tuning SD – Initial Map Configuration”section for more details. Failure to raise these limits appropriately could result in engine damage as the calculated airflow and/or load becomes static past a certain point. MANIFOLD PRESSURE SENSOR CHECK ENGINE LIGHT ERRATIC LOAD CALCULATION Any diagnostic trouble code (DTC) related to the manifold pressure sensor will cause the Subaru ECU to estimate manifold absolute pressure (MAP) based on the current calculated load (as a failsafe).
This can result in an erratic load calculation in SD mode because actual MAP (a key input for SD) would no longer be determined correctly. If this occurs when the vehicle is accelerating, a lean condition and incorrect timing can result. It will also likely cause the engine to eventually stall. If there is the possibility that any of the MAP sensor related DTCs (P0068, P0107, or P0108) could be triggered, it is critical that those DTCs are disabled in the tune. The installation of an aftermarket MAP sensor (required for SD if the factory MAP sensor is not sufficient) will make it more likely for these DTCs to be triggered, even though there may be nothing wrong with the sensor itself.
Please see“Tuning SD – Initial Map Configuration”section for more details.
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ENGINE HARDWARE CHANGES MAY REQUIRE A RE-TUNE FOR SD It is important to understand that after the SD tune is complete for a given car, any further changes to engine hardware that impacts airflow efficiency in or out of the engine can potentially require tweaking or re-tuning of the VE table to avoid fueling/timing issues (due to incorrectly calculated SD load). Additionally, mechanical issues, such as intake/exhaust leaks, and issues related to the aging of the motor, such as combustion deposits and loss of compression, can also impact actual VE.
It is highly recommended that a permanent wideband o2 sensor and gauge is installed in the vehicle and that the driver understands how to read the gauge and determine what is normal for their tune.
POTENTIAL RISKS FOR SD WITH A HEAT SOAKED IAT SENSOR Any SD calculation, including COBB SD, requires an input for cylinder charge temperature, which is critical to the determination of accurate airflow via SD. The estimation of cylinder change temperature is accomplished for COBB SD via the IAT sensor input. Generally, when the IAT sensor is in the recommended location (post-IC), the vehicle is moving and the driver is on the throttle, the IAT input can be a fairly reliable representation of actual cylinder charge temp. However, when the vehicle is sitting still (or at low speeds) and the driver is off the throttle (or low throttle), or the vehicle has been sitting with the engine off and a hot engine bay for a period of time, there is the potential for the IAT sensor to become heat soaked.
That is, the sensor now reads higher than the actual intake air temp. When SD is active, this would cause the calculated SD airflow (as well as load) to be lower than it should be, causing the car to run lean (and with generally more timing advance). This effect may subside after the vehicle gets moving and throttle (as well as MAP) increases, but it will generally not be an instantaneous improvement. As such, it is critical that the owner/driver of the car understands the specific scenarios in which a heat soaked IAT sensor can potentially occur and to avoid putting the car under high load when these scenarios are present (and for a period shortly after).
This is another reason why a wideband o2 sensor and gauge should be installed in the car and that the driver instructed on how to determine when fueling is incorrect.
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