Subaru DIT V4.0 CCF (Gen2) Additions

Overview

With the progression of the Subaru DIT platform, there was an increased need to exceed factory load, boost and IPW (injector pulse width) limits. COBB has implemented a series of changes to facilitate those needs. Load of up to 10.0 can now be achieved without undesirable behavior, boost up to 100 psi (absolute), and the IPW limit has been increased sufficiently to avoid impacting normal operation. Additionally, a new "MAF Simple" feature allows for an airflow calculation based on the MAF Calibration table without intervention of the MAF Corrected Volumetric Efficiency Input... tables and other complex background systems. A number of other features were also added to further aid in the DIT tuning process.

As always, our engineers have made things as seamless as possible, but due to the extensive changes necessary to achieve these goals, we've produced this guide to help understand how the new features work and what they can do for you.

Load Limit Increase

In order to facilitate load beyond the factory 3.3 limit, tables needed for high load calibration have been created, as well as a new monitor. All of the new tables can be found in the "COBB Custom Features" → "Load Extend Tables" folder in Accesstuner. These tables can also be found in their traditional folder locations, and within the "Flex Fuel Tables (Group A)" and "...(Group B)" folders if they are flex fuel enabled.

In order to keep functions not related to high load operation intact, the factory Calculated Load monitor remains, and a new Calculated Load Extended monitor has been created. When tuning a vehicle that can achieve beyond the factory 3.3 limit, be sure to log Calculated Load Extended so you can see the actual value.

The extended load tables have a new limit of 10.2 which should facilitate engine making ~1000 ft lbs of torque or less without requiring any skewing of load.

Boost Limit Increase

In order to facilitate boost beyond the factory 24.x psi limit (relative to sea level), tables needed for high boost calibration have been created, as well as new monitors. All of the new tables can be found in the "COBB Custom Features" → "Boost Extend Tables" folder in Accesstuner. These tables can also be found in their traditional folder locations, and within the "Flex Fuel Tables (Group A)" and "...(Group B)" folders if they are flex fuel enabled. ~87 psi (relative to sea level) or ~100 psi (absolute) are the new max values you can enter in most of these tables. 

These changes allow for higher limits for boost targeting, boost limits fuel cut, and boost monitoring. You will also need an aftermarket MAP sensor with the appropriate higher range in order to read beyond the factory limits. This sensor will need to be calibrated via the MAP Sensor Calibration (Multiplier) and MAP Sensor Calibration (Offset) tables (in the "Sensor Calibrations" folder) → see your MAP sensor manufacturer's documentation to determine how the sensor should be scaled.

In order to keep functions not related to high boost operation intact, the factory Manifold Abs. Pressure monitor remains, and new Manifold Abs. Pressure Extended... monitors have been created. When tuning a vehicle that can achieve beyond the factory limit, be sure to log the associated Extended monitor so you can see the actual value.

The following is a list of the new monitors related to this system. See the Subaru Custom Monitor List for descriptions of each monitor. 

• Manifold Abs Pressure Extended BOOST CONTROL

• Manifold Abs Pressure Extended OTHER

• Manifold Abs Pressure Extended RAW
• Manifold Abs Pressure Extended SD
• Manifold Abs. Pressure Sensor Voltage
• Manifold Rel Pressure Extended

IPW Limit Increase

In order to facilitate IPW beyond a stock hard coded limit pre-fuel pressure compensation, custom code has enabled a new limit more than 10x the stock one, making it unlikely to ever be exceeded. The old factory limit could be hit at higher loads, causing a lean condition where IPW goes static at about 7.x ms at WOT (post-fuel pressure compensation). We'll spare you further details, just know the hard coded IPW limit is no longer a concern.

MAF Simple - Alternate Airflow Model

The MAF Simple system is designed to make MAF-based calibration easier and more efficient. We also feel this system has greater accuracy at moderate to high load and boost levels.

This system allows you to transition from the highly complex factory airflow model, which includes the MAF Corrected Volumetric Efficiency Input... tables and many others, to a simple MAF calibration based airflow calculation more similar to an EJ engine. In testing we found great results at higher airflow, but using the simplified model had adverse affects at very low airflow so we have set the activation load threshold limit accordingly. All settings can be found in the "COBB Custom Features" → "MAF Simple" folder.

We have set the system based on values that worked well in testing, but left the MAF Simple Mode Activation Threshold (Min. Load) table set higher so it will be unlikely to alter behavior of your existing maps on vehicles that don't exceed 3.2 load. You may want to try lower values as we've found MAF Simple more accurately represented actual airflow during spoolup on FMIC-equipped vehicles.

This system only impacts the final airflow when SD Mode is MAF or Hybrid, and in the case of Hybrid, only when MAF is active. The engine must also be over the MAF Simple Mode Activation Threshold (Min. Load) table OR over an internal (non-tunable) manifold pressure threshold of 38 psi (absolute) to activate. The MAF Simple airflow value is always calculated (even when MAF Simple is not active) so it can be monitored and tuned before applying the value to final airflow, if desired.

Upon activation, ramping between the factory airflow model and MAF Simple will occur, and you can alter that rate via the MAF Simple Mode Ramping Adder (OEM to Simple) table. If load or MAP drops below the corresponding activation threshold (minus the hysteresis value), the OEM airflow model will resume. Ramping rate when moving to the OEM model can be adjusted via the MAF Simple Mode Ramping Adder (Simple to OEM) table.

The following is a list of the new monitors related to this system. See the Subaru Custom Monitor List for descriptions of each monitor. 

• MAF Simple to OEM Airflow Ratio
• Mass Airflow Corrected FINAL
• Mass Airflow Corrected SIMPLE
• Mass Airflow Corrected OEM
• Mass Airflow TABLE

Manifold Pressure Smoothing

Manifold Pressure can be smoothed by separate factors for boost control and for the COBB SD airflow calculation via the following tables (see table descriptions for details): 

• Manifold Pressure Smoothing Factor (Boost Control) → found in the "COBB Custom Features" - > "Boost Smoothing" group. This table is real-time tunable.
  
  
• Manifold Pressure Smoothing Factor (SD) → found in the "COBB Custom Features" - > "Boost Smoothing" group. This table is also real-time tunable.

Smoothing is a means of filtering out "noise" in a value by considering the change in the current value versus the previous value. It will tend to dampen larger short-term changes. The dampening effect is dependent on the smoothing factor used in the filtered calculation. Higher smoothing factor values result in less smoothing (more responsive to spikes in current sensor data), while lower values result in more smoothing (less responsive to spikes in current sensor data). A smoothing factor of 1.0000 will disable smoothing altogether. 

Boost Gauge Wrap

This feature allows the factory boost display to to read up to the factory boost gauge's max of 24.0 psi and then "wrap" to show higher boost levels.

• Gauge will wrap-around when 24 psi is exceeded, allowing you to effectively read up to 44 psi of boost (with default tuning set up - potentially higher with additional tuning changes).
  
  
• Default set up uses a 20 psi base in Wrap mode making it easy to calculate the new boost level in your head - 10 psi on gauge when wrapped is 30 psi actual (20 + 10 = 30).
  
  
• Can be customized with a different wrap threshold and/or different base offset. Or can be disabled if not desired (feature is enabled by default).
  
  
• See table descriptions in the "Cobb Custom Features" → "Boost Gauge Wrap" folder for additional details.

NOTE: The boost wrap feature cannot represent boost higher than the MAP sensor installed to the car is capable of reading. A correct barometric pressure reading is also required for the feature to work properly.

Intake Temperature Source Selection

This feature allows using manifold temperature in place of pre-turbo intake temperature for all applicable tables and other functions in the ECU. This feature was originally introduced for the 18-19 WRX and now is available for the 15-17 WRX as well. It can be activated in the tune by setting the Intake Temp. Chosen Source (0 = Pre-Turbo Sensor (MAF), 1 = Manifold Sensor) table to 1 (found in the "COBB Custom Features" → "Intake Temp. Source Selection" folder). The Intake Temperature Pre Turbo monitor will still allow you to log the actual pre-turbo temperature even when this feature is active. 

Subaru Battery Life & Other OEM Updates

This ECU type includes the latest Subaru ECU logic/calibration for the DIT WRX, including battery life improvements for 15-17 WRX (18+ WRX already included Subaru battery life changes).

TGV Duplication Mode

Adds a feature to DIT (previously available for EJ 2.5L) to allow duplicating (with conversion), the TGV input signal (as used by factory ECU logic) from one side (left or right) to the opposite side where one TGV side is being used for a custom input. This facilitates operation of the TGV system while also using one side for an additional input. This feature can be activated via the following table (see table description in Accesstuner for details):

Custom Sensor Input TGV Duplication Mode (0 = Disabled, 1 = Copy Left to Right [custom sensor wired to right], 2 = Copy Right to Left [custom sensor wired to left]) → found in the "COBB Custom Features" → "Sensor Inputs (Custom)" folder.

Fuel Economy Gauge Correction

Adds a feature to DIT (previously available for EJ 2.5L) to allow correction of the factory MPG gauge based on ethanol content (or without ethanol content if the Flex Fuel feature is disabled). This is tuned via the following tables (see table description in Accesstuner for details):

Fuel Economy Display Correction Factor → found in the "Fuel Tables" → "Injectors" folder as well as the  "COBB Custom Features → "Flex Fuel" → "Flex Fuel Tables (Group A)" folder .

Fuel Economy Display Correction Factor (Flex Fuel B) → found in the "COBB Custom Features" → "Flex Fuel" → "Flex Fuel Tables (Group B)" folder.

Dynamic Advance Changes

Dynamic Advance in Subaru DIT Engines

Knock Sum Monitor

A new Knock Sum monitor increments when the ECU's knock signal algorithm perceives a knock event. This knock signal is the same signal used for all knock responses by the ECU (feedback knock correction, fine knock learning, and the DAM).

Unlike the Knock Sum monitor(s) for the EJ 2.5L, the DIT monitor will not generally increment at idle due to the factory minimum knock signal thresholds of 1000 RPM and 0.4 g/rev of load. However, it may still increment in areas where the ECU does not respond to knock → where the knock signal minimums are met but load and/or RPM are still below (or even above) thresholds for the ECU to respond to knock. The Knock Sum monitor will reset to 0 when turning the ignition ON. 

As is the case with the factory knock response, the Knock Sum monitor can change with false knock so the total value itself is not typically relevant. Instead, the conditions in the log when Knock Sum increments is generally more important.