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INTRODUCTION

This document outlines some of the unique engine control unit (ECU) logic and tuning strategies relevant to Subaru's 2.0L Direct Injection Turbo (DIT) models when compared to the EJ25 ECUs. Some general info here also applies to the 2.4L DIT models. It is not the intention of this document to outline every difference between the DIT and EJ25 ECUs, but rather the most notable differences (known to date) that can impact your ability to tune effectively.

For information about COBB Custom Feature (CCF) ECUs, check out the guide below:

• Subaru DIT V4.0 CCF (Gen2) Additions

APPLICABLE SUBARU MODELS

The following Subaru models are applicable to this document:

• 2014 - 2018 Subaru Forester XT

• 2015 - 2021 Subaru WRX

TABLE DESCRIPTIONS

Besides this document, an additional resource for ECU logic details are the table descriptions shown in the Accesstuner software. These will show up in the lower left corner of the software for the current table that is selected. If not visible, make sure the "Table Description" check box is selected in the View menu. Additionally, the Help menu in the software contains links to documents that list all of these table descriptions as well as all of the data monitor descriptions.

CONTACT US

COBB authorized Protuners are welcome to contact us with any additional questions/concerns or when in need of troubleshooting assistance.

FUELING

GLOBAL FUELING ADJUSTMENT FOR E85 OR OTHER ETHANOL CONCENTRATIONS (NON-FLEX FUEL ECUs)

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The following outlines the steps necessary to account for a global fuel adjustment for E85 (or other ethanol concentrations) in your tune for ECUs that do not support the COBB Flex Fuel feature. This will also have the effect of modifying your cranking injector pulse width, meaning less tweaking necessary in that area of the tune.

If you want to start by adding 43% more fuel for the global adjustment for E85 (this could be more or less depending on the actual ethanol % in the tank), multiply all the injector pulse width compensation values in each of the three tables below by 1.43 (highlight entire table, hit M key and enter 1.43). From there, if you want to add or remove fuel, repeat this process (ex. +3% = multiply by 1.03, -3% = multiply by 0.97). Note: Fuel Rail Pressure values in these tables must NOT be changed.

• "Fuel Injector Trim (Fuel Pressure)(Multiplier)"

• "Fuel Injector Trim (Fuel Pressure)(Offset)"

LEAN PRIMARY OL FUELING DUE TO CL FUEL TARGET INTERACTION (AGGRESSIVE START)

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There is a specific interaction between the closed loop and open loop fuel targets in the factory logic, that, with particular changes to the tune, can result in an override of the normal open loop fueling with much leaner targets. The "Closed Loop Fueling Target Final (Alternate)(Aggressive Start)(Primary OL Fuel Compare)" table is an alternate final closed loop fueling target that overrides the normal final closed loop fueling target during an entire high throttle run when that run was started with aggressive accelerator pedal movement (i.e. "throttle mash") and when the target called for by this table is richer than what would be dictated by the primary open loop map target (even though it is still in closed loop). In the factory tune, this would only have an effect in closed loop. However, if you modify your tune so that the primary open loop fueling target (as dictated by the Primary Open Loop Fueling tables) is leaner than this table's value (and aggressive start conditions for run are met), when the switch to open loop is made the ECU will set the final primary open loop map target to 14.7:1 AFR and only the "Primary Open Loop Fueling Min. Enrichment" table will come into play. To avoid this, you can do one of the following:

• Set the "Closed Loop Fueling Target Final (Alternate)(Aggressive Start)(Primary OL Fuel Compare)" table to always be leaner than what would be dictated by the primary OL fuel map target (especially in open loop)
  
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• Set the "Closed Loop Fueling Target Final (Alternate)(Aggressive Start)(Primary OL Fuel Compare) Activation (Min. Coolant Temp)" table to its maximum value (ex. 248 deg. F) or set the "Closed Loop Fueling Target Final (Alternate)(Aggressive Start)(Primary OL Fuel Compare) Activation (Max. Coolant Temp)" table to its minimum value (ex. -40 deg.) which will disable the switching all together (in both open and closed loop). As of this writing, our OTS performance maps are set to disable the logic using this method. However, you should confirm this in the tune if you are using an OTS map.

A/F LEARNING #1 LOAD RANGES

Long-term fuel trims (A/F Learning #1) for DIT Subarus are similar in logic to non-DIT Subarus, but there are many more stored values. There are a total of 12 stored A/F Learning #1 trims: 2 at idle (Idle 1 and Idle 2) and 10 applied outside of idle (A1-E1 and A2-E2). The non-idle trims are stored across specific load ranges but there is an RPM breakpoint that determines the split between group 1 (A1-E1) and group 2 (A2-E2) non-idle trims. The same RPM breakpoint also determines the split between the Idle 1 and Idle 2 trims.

A/F LEARNING #1 (GLOBAL ADJUSTMENT) MIN/MAX

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These tables give you the ability to adjust the min/max limits for the global A/F Learning #1 adjustment. This global adjustment can occur after a reset or reflash when specific conditions are met during stable closed loop operation (typically at idle). When the ECU dictates that a global adjustment should occur, all A/F Learning #1 ranges (A1-E1, A2-E2, Idle 1 and Idle 2) are overridden with a current learned trim and then the ECU returns to normal A/F Learning #1 operation. This can cause, for example, fueling changes at WOT that are undesirable (due to this globally applied long-term trim). You can override the allowed global adjustment trims by setting these Min and Max limits to zero (this will set all the trims to zero when the global adjustment is called for). Or if you want to retain the global adjustment, but do not want the higher load ranges to be effected, you can modify the individual A/F Learning #1 load range Min/Max values as described in the next section (this will impact normal A/F Learning trims as well in the ranges modified).

A/F LEARNING #1 INDIVIDUAL LIMITS FOR EACH LOAD RANGE (15+ WRX ONLY)

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These tables give you the ability to individually determine the minimum and maximum limits for each A/F Learning #1 load range (see A/F LEARNING #1 LOAD RANGES section earlier in this document for details on the load ranges). This allows you to, for example, disable A/F Learning #1 in the higher load ranges so that trims (when in closed loop in that range) are not carried over to your WOT fueling. This also will prevent or allow you to minimize the "global" A/F Learning #1 adjustment in specific load ranges while not disabling the global adjustment entirely (see previous section for more details on the global adjustment). The Min/Max for the A/F Learning #1 Idle 1 and Idle 2 trims can also be adjusted separately from the non-idle limits.

FUEL MODES

The DIT ECU has two primary fueling modes: stratified warm-up (inject fuel during intake and compression strokes) and homogeneous (inject fuel during intake stroke). You will see that the various warm-up and post-start enrichment tables are split across these modes. Stratified warm-up mode is active primarily for a short period of time after engine start except at higher ECTs. Typically, any amount of throttle will cause the switch from stratified to homogeneous fuel mode, so stratified mode is primarily an idle warm-up mode (blipping the throttle at idle will cause a switch from stratified to homogeneous mode and then back to stratified). Homogeneous mode will be active the vast majority of the time. You can determine the current fuel mode by logging/viewing the "Fuel Mode" monitor (1 = homogenous mode, 2 = stratified mode).

RICH CL TARGET FORCE OPEN LOOP

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When the closed loop fuel target is richer than a specific threshold ("Closed Loop Fueling Target Final Rich Threshold (Switch to OL)" table in the "Fuel Tables" → "Closed Loop Target" group), the ECU will switch to open loop fueling. If you are holding closed loop at higher load in your tune, you may need to adjust this table to avoid an unintentional switch to open loop.

ALTERNATE PRIMARY OL FUEL TARGET AND FORCE OPEN LOOP 

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At higher load, the ECU may, at times, apply a minimum enrichment that is similar to the factory primary open loop "Base" calibration. This can potentially cause your open loop fueling target to be richer than expected and can also force open loop fueling operation (when this minimum is richer than 14.7:1 AFR) even if the rest of the tune dictates closed loop operation. To eliminate this minimum enrichment and forced open loop from coming into play, set the "Primary Open Loop Fueling Min. Enrichment (Pre-Final)(Force OL) Activation Threshold" table to 65535 (under "Fuel Tables" → "Open Loop (Primary)" table group). Note: Not applicable to 15 WRX Post-recall 1 or 14-15 FXT ECUs.

FORCE FULL-TIME CLOSED LOOP

The following are steps to force the DIT ECU into full-time closed loop. Warning: After making these changes, verify that the ECU remains in closed loop at high load by testing on the car.

• In the "Fuel Tables" → "Closed Loop Target" table group:

  • Tune the four "Closed Loop Fueling Target Base (Main)..." A,B,C,D tables to reflect your desired full-time closed loop fuel targets.

  • Set the "Closed Loop Fueling Target Final (Alternate)(Aggressive Start)(Primary OL Fuel Compare) Activation (Max. Coolant Temp)" table to -40 - this disables the "aggressive start" table alternate closed loop target from coming into play.

• In the "Fuel Tables" → "Closed/Open Loop Transition..." → "Delay" table group:

  • Set the delay values in the "Closed to Open Loop Delays" table to 65535 across the entire table.

• In the "Fuel Tables" → "Closed/Open Loop Transition..." → "Delay Deactivation Thresholds" table group:

  • Set all the "Load vs. Rpm Component" raw values (z-axis) of the following tables to zero:

    • Closed Loop Delay Max. Load vs. RPM Component Determine (Alternate) - (15+ WRX/16+ FXT only)

    • Closed Loop Delay Max. Load vs. RPM Component Determine (Primary Fuel Min. Activation Met)

    • Closed Loop Delay Max. Load vs. RPM Component Determine (Primary Fuel Min. Activation NOT Met) 

  • Make sure the "Closed Loop Delay Max. Load vs. RPM Component Threshold (Smoothing Factor 1)" and "...(Smoothing Factor 2)" tables are both set to 65535. 

  • Set all the Engine Speed (RPM) value(s) in the "Closed Loop Delay Max. RPM (Per Gear)" or "Closed Loop Delay Max. RPM" table to 12800.

  • If you tuned any of the remaining tables in this table group to non-stock values, return these to stock. Failure to do so can cause switching to open loop. 

• In the "Fuel Tables" → "Closed/Open Loop Transition..." → "Transition Thresholds (Alternate)" table group:

  • Set the "Closed Loop Fueling Target Final Rich Threshold (Switch to OL)" table to 4.900:1 AFR.

• In the "Fuel Tables" → "Closed/Open Loop Transition..." → "Transition Thresholds (Delay Active)" table group:

  • Set all the Calculated Load (g/rev) values (z-axis) in the "Closed/Open Loop Transition with Delay (Min. Load)" table to their maximum value. 

• In the "Fuel Tables" → "Open Loop (Primary)" table group: 

  • Tune the "Primary Open Loop Fueling Base" table(s) as you would normally just in case you have an issue with the car switching to open loop unexpectedly (or if a sensor failure or similar causes full-time open loop failsafe).

  • Change the "Primary Open Loop Fueling Min. Enrichment (Pre-Final)(Force OL) Activation Threshold" table to 65535. Note: Not applicable to 15 WRX Post-recall 1 or 14-15 FXT ECUs.

LIMITS (BOOST/FUEL/LOAD/THROTTLE)

FUEL CUT LIMITER MODES

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Fuel cut limiters work a little differently for this ECU. There are additional thresholds for each of these limiters that enable a "Mode" that must be active otherwise the fuel cut limiter will not be activated even if the primary fuel cut threshold is exceeded. In the factory tune, these Mode thresholds are set to activate before the fuel cut event would take place. For example, with the rev limiter in the factory tune (15 WRX 6MT), the rev limit Mode will turn on above 6700 RPM and off below 6600 RPM. On the other hand, the fuel cut rev limiter threshold will turn on above 6700 RPM and turn off below 6700 RPM (i.e. basically no hysteresis). The other fuel cut limiter with the Mode requirement is the fuel cut based speed limiter.

WARNING: Failure to account for the Mode activation when changing either of these fuel cut limiters can cause the limiter to be disabled or come in later than expected. The boost limit fuel cut also has a Mode requirement but we've set this up so that you cannot disable this Mode (i.e. when the boost limit fuel cut is called for, fuel cut will always take place).

BOOST LIMITS

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The boost limiter is set up a little differently for the DIT Subarus. The boost level above which fuel will be cut (and P0244 DTC enabled) is calculated as follows:
("Boost Limits Base" table value with all Boost Targets Compensations applied)
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("Boost Limits Base Adder (Fuel Cut)(Wastegate Solenoid DTC)" table value)