Tech Bulletin - 2017 WRX STI - Subaru Logic and OTS Calibration Changes



Tech Bulletin - 2017 WRX STI - Subaru Logic and OTS Calibration Changes

Date: 7/29/16
By: Mike McGinnis

Vehicles affected:

  • 2017 Subaru WRX STI

Software affected:

  • and newer

Firmware affected:

  • not applicable


While 2017 model year WRX STI vehicles remains largely the same as 2015-2016, there are critical changes Subaru and COBB have made that we would like to make you aware of:

  1. CCF (COBB Custom Features) only - Rather than offering 3 different ECU types for this model year (MAF, MAF/SD, CCF), we are providing the one with all the features, CCF. This does not mean you need to use all the features, but they are all available. This helps Protuners take best advantage of the map compare feature as you build a library of tunes and simplifies/expedites customer support and future software updates.

    1. As with previous Subaru CCF files, table axes are labelled "Reflash-only" and operate as such. Please ensure your customers know to change map via Reflash rather than Realtime if they are changing between maps that do not have the same x/y data.


  2. Closed loop fuel control has been expanded and altered significantly.

    1. Rather than closed loop targets being determined solely by tables COBB has organized in the "Closed Loop Targets" folder in Accesstuner, Primary OL (open loop) values now affect closed loop targets under certain conditions.

    2. The tables common to prior model years that used to determine CL/OL transition now determine when the Primary OL Fueling targets become applied to CL (closed loop) targets. When these thresholds are exceeded, the Primary OL target AFR becomes applied to the CL target as an offset from stoich i.e. Primary OL target 14.0 results in -0.7 offset of the CL target AFR. Closed loop compensations are still applied as usual to calculate the final CL target.

    3. There are new tables, values, and logic to govern the transition to open loop. The result of "Closed/Open Loop Transition Main (Closed Loop Fueling Target)(Closed Loop Switch Lean Threshold)" plus "Closed/Open Loop Transition Main (Closed Loop Fueling Target)(Open Loop Switch Rich Adder)" determines the closed loop target AFR the crossover from CL to OL occurs at.

    4. We do not suggest manipulating calibrations to make the ECU operate in closed loop full time, or richer than 12.5 gas AFR, due to the range of accuracy of the OEM front oxygen sensor.

    5. Please note the "Closed Loop Fueling Target Compensation (Load)" tables no longer have large corrections at high RPM, load. If you keep these values small it will avoid large disparities between CL target and OL target, if doing so is your goal.
    6. If you fall in love with this behavior: While it cannot be duplicated on previous model years due to the associated logic changes, the CL target load compensation tables and associated values can be altered to achieve similar results. If interested, contact the Subaru Expert group for details.


  3. OTS changes to leverage this closed loop behavior:

    1. The following tables have been changed to allow closed loop fuel control over a broader range of conditions than previous OTS calibrations:

      1. Closed Loop Fueling Target Dynamic Lean Limit Floor

      2. Closed Loop Fueling Target Force Open Loop Exit (Rich Limit)

      3. Closed Loop Delay Max. Load (RPM)

      4. Closed Loop Delay Max. Load vs. RPM Component Threshold (Smoothing Factor 1)

      5. Closed Loop Delay Max. Load vs. RPM Component Threshold (Smoothing Factor 2)

      6. Closed Loop Delay Max. Load vs. RPM Component Threshold (Smoothing Factor 3)

    2. OTS calibrations now remain in closed loop until closed loop target AFR is richer than 12.5. Since primary Open Loop Fuel table values affect CL targets once our low OTS values for "Closed Loop Delay Max. Load (RPM)" have been exceeded, please ensure the values you use in those tables will generate the resultant CL target air fuel ratios you wish to achieve.

    3. Since closed loop control keeps the engine operating on AFR target, smoother and more consistent engine operation can be expected as long as calibration values are appropriate. This will be most noticeable during moderate load conditions i.e. going up hill at highway speed.

    4. Since the vehicle will be operating in closed loop over the full AFR range we deem the front oxygen sensor trustworthy (when in good working order, with no exhaust leaks, etc.), we have disabled CL to OL transition delays. Once the max rich target AFR is exceeded, the car will immediately enter open loop operation.


  4. MAP voltage thresholds - MY17 CCF will include changes to improve error checking. It does not share threshold calibration data with SD and CCF from previous years. Tuners will need to alter these values appropriately when using aftermarket MAP sensors.

  5. Load Compensation (Manifold Pressure) - Please note the large changes in these table values compared to MY16. We confirmed MY16 values did not work well on a MY17 car. Please be prepared to adjust accordingly if you attempt to use calibration data from one of your MY16 STI tunes on a MY17 vehicle.

  6. Primary Open Loop Fueling - While some things have been zeroed out that simplify calibration, Subaru has added an additional pair of Primary OL Fuel tables. You willl find TGV closed and open versions of the standard and high detonation tables.

  7. Ignition Timing Compensation (CL to OL Transition Delay) - This logic is not new for MY17, but we have chosen to avoid this timing reduction in MY17 COBB OTS maps by setting the table Z data to zeroes. Should you feel the need to use this function, we have not altered its behavior.

  8. Primary Open Loop Fueling Compensation (Closed Loop Delay Max. Load Not Exceeded) - This table and the "Min." table that otherwise shares the name can potentially prevent a vehicle from going into open loop. While they didn't interfere with operation during OTS testing, we have zeroed them out to avoid potential interference with your calibrations.

Minor Subaru OEM calibration changes:

  1. Closed Loop Fueling Target Compensation (Coolant Temp) - Subaru has reduced the target enrichment at some temperatures and loads, including some cells which have been reduced to zero. If you are tuning a vehicle with fuel system modifications beyond our COBB staged progression, or are running fuel with higher than 10% ethanol content, you may find a greater need to alter values in these tables than in the past. Smaller changes have been made to the "Warm-Up Enrichment Primary" tables.

  2. TPS-Related Fuel Adder - It is still present, but the High and Low adder values have been zeroed out.

  3. Primary OL Fueling Compensation (Coolant Temp) - Subaru has zeroed out this table. Previously it contained rather large corrections at cold temperatures and moderate ones under conditions customers are more likely to encounter.

Tables Subaru altered that we changed back to MY15-16 values:

  1. AF Learning - Subaru altered AF learning 1 break points and percent limits significantly for 2017, but we have made MY17 OTS calibrations mirror MY15-16 OTS calibrations. Should you choose to employ Subaru’s new breakpoints and percent limits, please be mindful of potential consequences.


  2. DAM related values - "Coarse Knock Learning (DAM) Mode Fine Learning Threshold (Neg)" and "Coarse Knock Learning (DAM) Mode Min. Dyn. Adv. Map Value" changed in MY17. We have set these values to mirror MY15-16 in our OTS maps in case Subaru's new values would cause unintended consequences in Protuner calibrations.


Time is money. We hope this Tech Bulletin combined with OTS performance maps which include these MY17 STI calibration updates allow you to more efficiently start tuning these new vehicles!

While Subaru made a few more calibration tweaks for MY17, we have avoided mentioning those which likely will not impact your work. If you have any feedback, questions, or concerns please let our Subaru Expert Group know!

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