Subaru Fuel Mileage Display Correction Guide

Version 1.0

11/16/2015

Methods

COBB Custom Features offer two different methods for correcting the in-cabin fuel mileage display (FMD):

• For EJ 2.5L CCF, Auto Correction mode that recalculates the FMD value based on current ethanol content and fuel pressure compensation (when active). If an error is observed, further manual correction can be introduced.
  
  
• For EJ 2.5L CCF and DIT Gen2 CCF, Manual Correction mode that recalculates the FMD value based on the Fuel Economy Display Correction Factor Group A, Group B and Blending Ratio values.

In order to utilize the Auto Correction mode (EJ 2.5L only), please follow these steps:

• Complete tune for vehicle; Flex Fuel feature is compatible but not required. Ensure that Fuel Injector Scale values are correct within normal margin of error.
  
  
  • If the MAF Calibration (MAF Mode) or SD Volumetric Efficiency table (SD Mode) are used to artificially remove or add fuel to compensate for an erroneous Fuel Injector Scale value(s), an incorrect mileage display calculation will result.
    
    
• Enable Auto Correction via the Fuel Economy Display Auto Correct table (set to 1).
  
  
• Verify (or set) the Fuel Economy Display Correction Factor Group A and Group B tables are set to 1.000 (no manual correction). Verify Blending Ratio table for Fuel Economy Display Correction Factor is set to linear E0-E100 scaling, or that it matches the Fuel Injector Scale blending ratio if alternate blending is used.
  
  
• Sanity check feature by monitoring or logging the Fuel Economy Display Correction FINAL monitor. This value will move when Ethanol Concentration FINAL changes (depending on blending table).
  
  
  • Values above 1.00 indicate correction for when Fuel Injector Scale (injector size is larger) is smaller than stock; the inverse is true for injectors smaller than stock.
    
    
• If the reported dash FMD values do not match the actual manually calculated fuel mileage, this can be corrected by adjusting the Fuel Economy Display Correction Factor tables for Group A and/or B.
  
  
  • To adjust values based on manual fuel mileage calculations, apply the following formula: "(FMD Mileage Value / Actual Fuel Mileage Value) * Current Table Correction Value".

In order to utilize Manual Correction mode, please follow these steps:

• Complete tune for vehicle; Flex Fuel feature is compatible but not required.
  
  
• Ensure that Fuel Injector Scale values (EJ 2.5L) or Fuel Injector Trim (Fuel Pressure)(Multiplier) (DIT) values are correct within normal margin of error.
  
  
  • If the MAF Calibration (MAF Mode) or SD Volumetric Efficiency table(s) (SD Mode) are used to artificially remove or add fuel to compensate for an erroneous Fuel Injector Scale (EJ 2.5L) or Fuel Injector Trim (Fuel Pressure)(Multiplier) (DIT) values, an incorrect mileage display calculation will result.
    
    
• For EJ 2.5L, disable Auto Correction via the Fuel Economy Display Auto Correct table (set to 0).
  
  
• Verify Blending Ratio table for Fuel Economy Display Correction Factor is set to linear E0-E100 scaling, or that it matches the Fuel Injector Scale (EJ 2.5L) or Fuel Injector Trim (Fuel Pressure)(Multiplier) (DIT) blending ratio if alternate blending is used.
  
  
• Set the Fuel Economy Display Correction Factor table for Group A and Group B tables.
  
  
  • To calculate each value, divide the Factory Fuel Injector Scale (EJ 2.5L) or Factory Fuel Injector Trim (Fuel Pressure)(Multiplier) (DIT) table value(s) by the applicable Group A or Group B corresponding table values.
    
    
  • If using the FF feature, the low ethanol table (typically A) Fuel Economy Display Correction value should be larger than the high ethanol table (typically B).
    
    
• Sanity check feature by monitoring or logging the Fuel Economy Display Correction FINAL monitor. This value will move when Ethanol Concentration (Final) changes (depending on blending table).
  
  
  • For EJ 2.5L, values above 1.00 indicate correction for when Fuel Injector Scale (injector size is larger) is smaller than stock; the inverse is true for injectors smaller than stock.
    
    
• If the reported dash FMD values do not match the actual manually calculated fuel mileage, this can be corrected by adjusting the Fuel Economy Display Correction Factor tables for Group A and/or B.
  
  
  • To adjust values based on manual fuel mileage calculations, apply the following formula: "(FMD Mileage Value / Actual Fuel Mileage Value) * Current Table Correction Value".