Subaru Accesstuner Tuning Guide

Prepared by: Lance Lucas

12/10/2013

COBB and Injector Dynamics Injector Characterization Data: http://help.injectordynamics.com/support/solutions/articles/4000009270-cobb-subaru

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• This page is maintained by COBB's Director of Protuning and includes web links for our Accesstuner Pro software builds, information about COBB-provide training options, links to various logos to use within your marketing materials, etc.

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Factory EMS and Hardware Overview

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Boost control is also a simplistic yet effective system. The factory "2-port" boost control solenoid, which is plumbed via bleed style operation and is powered by the ECU via 12v PWM signal, operates on a 0-100% duty cycle scale using a closed loop boost targeting system. When energized, the solenoid is a low-pressure vent between the compressor nipple (boost reference) and the wastegate actuator, causing effective pressure at the actuator to decrease and boost to rise. A variety of restrictor pills are used within the boost control vacuum lines by the factory to fine-tune the system's responsiveness. A base wastegate duty cycle value is referenced, actual vs. target boost is evaluated, and corrections or "dynamics" are applied to correct for the boost error. This system is commonly upgraded to a plug-and-play "3-port" boost control solenoid with vacuum lines replumbed to operate the actuator in interrupt mode, where 100% wastegate duty cycle represents a complete blockage of boost reference to the wastegate actuator. The factory control system is highly scalable; it has proven effective for controlling small turbos making less than 15psi and 200whp all the way up to full motorsports vehicles running in excess of 30psi and 600whp. More detail about the factory system is available a thorough document entitled "How Subaru's Factory Boost Control System Works" by Christian Krahenbuhl.

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• Total Ignition Timing (all 2.5L): Primary Ignition + (Dynamic Advance * DAM) + Feedback Knock Correction + Fine Knock Learning + Compensations
• Total Ignition Timing (only 2.0L): Primary Ignition + (Dynamic Advance * (DAM/16)) + Feedback Knock Correction + Fine Knock Learning + Compensations

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Terminology Definitions

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• Knock Sum (where applicable): This is a somewhat arbitrary monitor and logging value that should only be analyzed under the specific conditions you wish to evaluate, such as during wide-open throttle (WOT) operation over a set RPM range. Some later ECUs can report Knock Sum on a per-cylinder level, some only on a global basis. It is useful to determine if a particular cylinder is especially prone to detonation in relation to the others; however it must be noted that Cylinders #1-3 lack knock detection accuracy due to their relative distance from the knock sensor. Cylinder #4 can be heard most reliably thanks to being located directly below the knock sensor, which has a difficult time perceiving real engine noise over the noisy boxer engine on the more distant cylinders. If a noise is perceived, this value will increment at all times, regardless of if the knock detection system is deemed to be accurate or not. It is not uncommon to see these values increment under even the most mundane conditions, such as idling or while operating the vehicle at slow speeds in a parking lot. It must be emphasized that this is simply an indicator that a noise of unknown source has been detected, which must still be evaluated by the ECU for source, sanity and plausibility (IE, is it likely that the engine is actually detonating and on which cylinders).
  
  
• Compensations: Within the framework above, this is a summation of various ignition timing compensations. Depending on the year and model, these exist on as per-cylinder corrections, per-gear adjustments, intake air temperature based adjustments, etc. Depending on how the compensation tables are calibrated and the conditions under which the vehicle is operated, these compensations can wildly alter total timing or conversely have a very small effect. We tend to use minute or zero compensation for "normal" operating conditions – such as mild temperatures at sea level elevation on a fully warm but not overheating engine – and then add compensations for when those types of conditions are at more extreme values, such as relatively cool or hot air temperatures, high elevations or when the engine is overheating.

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STi-Specific Considerations

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• Load _(grams/rev) = Final Mass Air Flow _{(grams/second)} ÷ Engine Speed _(revs/min) × 60 _(sacs/min)
  
  
  • Example: 300 / 6000 * 60 = 3.0 _(grams/rev)
    
    
• A/F Correction #1 = short-term fuel trim multiplier
  
  
  • Example: 1.0 = no change, 0.95 = -5% change, 1.05 = 5% change
    
    
• A/F Learning #1 = long-term fuel trim offset to short-term multiplier
  
  
  • Example: 0 = no change, -0.05 = -5% change, 0.05 = 5% change
    
    
• Final Fuel Multiplier = Final Fuel-Air EQ Ratio
  
  
  • Example: 1.10 = 10% richer than stoic. 0.90 = 10% leaner than stoich.
    
    
• Base IPW Calculation _{(microseconds)} = Final Fuel Multiplier × Fuel Injector Scale × Load × (A/F Corr. #1 + A/F Learn #1)
  
  
  • Example: 1.20 * 3150 * 3.0 *( .98 + .02) = 11340 _{(microseconds)}
    
    
• Final IPW _{(microseconds)} = Final Fuel Multiplier × Fuel Injector Scale × Load × (A/F Corr. #1 + A/F Learn #1) × Per Cylinder IPW Comp. × Small IPW Comp.
  
  
  • Note: Earlier ECUs do not have per-cylinder IPW compensation, but rather per-cylinder fuel multiplier compensation.
    
    
• Estimated Conversion for Injector Scalar to E0 Gasoline Flow Rate = 2707090 ÷ Fuel Injector Scale
  
  
  • Example: 2707090 / 4813 = _{562.45 ~(cc/min)}

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Injector Characterization

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