Octane Adjust Ratio (OAR) and How it works for Ford Vehicles

Octane Adjust Ratio


Applicable Model/Year: 

  • All supported EcoBoost vehicles 2013-16


Background:

The EcoBoost vehicles are equipped with several load, airflow, and torque limiting and targeting strategies.  These allow the vehicle to have consistent performance in varying environmental conditions and with different fuel quality.  However unlike many conventional tuning options there are no "boost targets" as boost can vary depending on driving conditions.  They are able to achieve this consistency and offer the ability to work on 87+ octane (though they recommend using 91+) through use of a dynamic multiplier called "OAR" which adjusts all of these strategies.


How it Works:

The OAR starts life at a value of 0.0 and is allowed to learn in both directions.  When fuel and sensor feedback are optimal the OAR will adjust towards -1.0.  When the feedback is less than optimal the OAR will trend towards +1.0.  It's likely that you're now wondering why it is that the multiplier is negative when it's happy and positive when it isn't, the reasoning is that the value is not a multiplier and not an offset, thus the ECU code can be simplified and use just a single table comprised entirely of negative values to cover the entire spectrum of operating conditions.  With an entire table of negative values it will be multiplied against, the negative multiplier from the optimal correction get's cancelled out into a positive timing correction, whereas the positive OAR value which is asking for things to get dialed back becomes negative and lowers the agression of timing.

OAR however does not just impact the timing.  In the event that fuel quality is less than optimal other strategies step in to remove stress and prevent damage to the engine automatically.  LSPI (low speed preignition) uses the OAR multiplier in order to blend several different load limit references in order to reduce the possibility of pre-ignition (detonation or knock).  Part-throttle combustion stability strategy uses the OAR to allow for casual driving at moderate load and allow for leaner fuel ratios to increase MPG but at the expense of heat.  Since this heat is generated much more rapidly on lower octane fuels which are already prone to detonation, the OAR steps in and makes adjustments in order to stave off the potential for disaster, while allowing your high horsepower machine the benefit of some decent MPG.

We here at COBB make an effort to utilize as many of the OEM tuning strategies as possible in order to offer the most advanced, powerful, and safest driving experience for you.  The majority of our calibrations utilize the OAR multiplier in the same fashion as the factory tunes do, however on our higher power tunes we want to be able to maximize performance for the specified octane, as a result in the event of even minor knock being sensed by the ECU we aggressively shift the OAR towards positive which lowers the agression of all values affected by the OAR.  Since we designed the OAR to be utilized in our tunes in order to maximize the potential of the available fuel type, it's very important to run the proper calibration for the fuel octane you are running.  When you initially install the Accessport the OAR will be reset.  Since OAR is a KAM (keep alive memory) stored value it may take a few days of driving in order to fully settle, however once learned the value will persist through start-up including when you change the map on your vehicle by using your Accessport.  The value may change from time to time based on knock sensor feedback and is completely normal and expected.


Available Adjustments and How to Make them:

Any adjustments involving the OAR ratio and it's related tables must be made using Accesstuner Software.  All of the tables can be found under the "Octane Adjust Ratio" folder under "Ignition Timing Tables"

  • Activation (Octane Adjust)

    • Oct. Adjustment Threshold Min. (ECT)

      • The minimum coolant temperature required to enable OAR

    • Oct. Adjustment Threshold Min. (Load)

      • The minimum load required to enable the OAR


  • Learning (Octane Adjust)

    • Maximum OAR

      • The maximum value allowed for the OAR

    • Minimum OAR
      • The minimum value allowed for the OAR

    • OAR Larning Modifier
      • Allows modification to the increment or decrement amount when conditions are met to change the learned OAR value.

    • OAR Listening Range (ECT) Disable
      • The maximum coolant temperature allowed before disabling OAR learning

    • OAR Listening Range (ECT)
      • The minimum coolant temperature required before enabling OAR learning

    • OAR Listening Range (Load) Disable
      • Maximum load allowed before disabling OAR learning

    • OAR listening Range (Load) Enable
      • Minimum load allowed before enabling OAR learning

    • OAR Listening Range (RPM) Disable
      • Maximum engine speed allowed before disabling OAR learning

    • OAR Listening Range (RPM) Enable
      • Minimum engine speed allowed before enabling OAR learning

0

  • Response (Octane Adjust)

    • Oct. Adjustment Timing Max. (Advance)

      • This table represents the maximum amount of timing advance that is needed to be considered running High octane.  If conditions are optimal the ECU will continue to dynamically add ignition timing through the use of OAR learning.

    • Oct. Adjustment Timing Max. (Retard)
      • This table represents the maximum amount of timing retard that is needed to be considered running low octane.  If conditions are less than optimal the ECU will continue to dynamically remove ignition timing through the use of OAR learning.

    • Oct. Adjustment Timing Mult. (Advance)
      • This table represents the multiplier to be used with the Oct. Adjustment Timing Max. (Advance) result.

    • Oct. Adjustment Timing Mult. (Retard)
      • This table represents the multiplier to be used with the OCT. Adjustment Timing Max. (Retard) result.


Things to look out for:

if you find that your OAR value does not stay near to -1.0 when using top tier fuels of the appropriate octane, please change the calibration on your map to a lower fuel octane until a better quality gasoline can be found.


Related Articles:

Ford Tuning Guide


Definitions:

  • AAT – Ambient Air Temperature
  • CCT – Catalytic Converter Temperature
  • ECT – Engine Coolant Temperature 
  • EOT – Engine Oil Temperature
  • EVT – Exhaust Valve Temperature
  • MBT – Minimum Timing for Best Torque
  • AFR – Air to Fuel Ratio (Lambda)
  • DC – Duty Cycle (used with various solenoids)
  • ECU – Engine Control Unit (also known as PCM)
  • MAP – Manifold Absolute Pressure (Post-Throttle)
  • OAR – Octane Adjust Ratio
  • FRP – Fuel Rail Pressure
  • LTT – Load To Torque
  • OTS – Off The Shelf
  • OB – Overboost
  • LSPI – Low Speed Pre-Ignition
  • HDFX – High Degree of Freedom Executive
  • CAT – Charge Air Temperature
  • COT – Compressor Outlet Temperature
  • EFT – Exhaust Flange Temperature
  • TOT – Transmission Oil Temperature
  • IAT – Intake Air Temperature
  • BL – Borderline (for ignition timing tables)
  • CL/OL – Closed Loop/Open Loop (for fueling tables) 
  • DTC – Diagnostic Trouble Code
  • O2 – Oxygen Sensor 
  • TIP – Throttle Inlet Pressure (Pre-Throttle) 
  • VCT – Variable Camshaft Timing
  • VSS – Vehicle Speed Signal (MPH/KPH)
  • TTL – Torque To Load
  • FBO – Full Bolt Ons
  • UB – Underboost
  • PD – Power Demand
  • VE – Volumetric Efficiency



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