Record, review and analyze data logs with a Cobb AccessPort.

Data Log: a recording of engine sensor data, normally used to diagnose, tune or trouble shoot an EFI engine. 

Reviewing a good data log is the best way to do a “check up” on your subaru. Ensuring all sensors are reading correctly, all fuel trims are within spec and the ecu isn’t trying to pull out any timing is VERY important part of owning any turbo charged car. 

2008 WRX tuned on 91oct. MT pump gas, low boost 15psi:

DIY Cobb AP data log video:

Opening and reviewing your Cobb AccessPort data log in MS Excel

Once you have opened the data log the first step to easy review is to “freeze” the top row so that as you scroll through the log you can still see the sensor name/data name in the top row.

This data log is WOT (100% throttle) pull in 3rd gear. A review of this log will show the engine/ECU are very happy with the current tune HOWEVER it also shows a problem with the air intake temp sensor (you can see this value is -40 the entire log).

Although this is not causing any problems in the data log it is something that should be addressed and fixed right away followed by a series of data logs to confirm everything is running correctly once the air temp sensor is working again.

Cobb Tuning Subaru data log

Data Log Parameter & Sensor Description for MAF based calibrations:

  1. AF correction – The current fuel correction factor being applied (this should be 0 during a WOT pull).
  2. AF Learning – The current LEARNED/stored fuel correction value being applied (this should be 0 during a WOT pull).
  3. AF sens 1 ratio AFR – The current air fuel ratio from the stock Subaru sensor **this sensor does not read correctly below ~12:1 afr. Any value richer than 12:1 should be checked against the wide band o2 sensor. In the case there is no wide band present as in this log you should see the value maxed out at 11.15 during high RPM/heavy load/boost over 10psi.
  4. Boost PSI – Current manifold pressure (post throttle body)
  5. Calc. Load – Calculated load value used by the ECU to determine fuel/ignition map look up values.
  6. Closed loop SW – closed loop/open loop switch *off means the ECU is operating in open loop*
  7. Dyn. Adv. Mult (DAM) – This is a VERY important value to monitor. A healthy happy Subaru should hold the max DAM value at all times. (value of 1 for new Subarus and 16 for older ECU models.) This means if you see the DAM value drop below the max value the ECU is hearing knock and is pulling timing. **If you see the DAM value drop this is something you should discuss with your tuner right away.** Some tuners will set the initial DAM value low letting the ECU increase the DAM slowly, this is ok but it is FAR better and safer to start the DAM initial value at its max and fully tune the ignition map/trims. 
  8. Dynamic advance (degree) – ignition timing value currently being added to ignition base map, Formula: DAM/max DAM value * current dynamic advance ignition map value. 
  9. FB knock – Feedback Knock correction. *this number should remain at 0, a negative # means the ECU pulled timing.
  10. FK learn – Fine knock learning *this number should remain at 0 95% of the time. This is the ECU’s first attempt to lower engine noise/knock. Even a well tuned engine will sometimes show a VERY small negative value here but 95% of the time it should remain at 0 as in this log.
  11. Ignition timing- Total ignition timing.
  12. Inj, duty – Injector Duty cycle *this value should not go over ~90%*
  13. MAF (G/S) – Mass Air Flow measured in Grams per second.
  14. MAF Volts – Mass Air Flow sensor voltage. *This value should not exceed 4.9 volts which is the limit of the MAFS.*
  15. RPM – Engine speed
  16. Throttle – Throttle position
  17. Intake temp – Intake air temp *In this log you can see the Air temp sensor is NOT working, this is something that needs to be addressed*. Normally the air temp value should not be more than 150% of the outside temp. 
  18. Waste gate duty – current waste gate duty cycle. *this log you can see values of 0, this is because the tune is set to run only 15psi and the waste gate spring pressure is 1 bar or 14.7psi there for the EBCS is not doing any work to make target boost.
  19. AP info – This should show the name of the current map/calibration used for the data log

Dyno Results from this log:

Data Log Parameters and Description used for Speed Density conversions aka MAP based tuning calibrations:

  1. AF correction – The current fuel correction factor being applied (this should be 0 during a WOT pull).
  2. AF Learning – The current LEARNED/stored fuel correction value being applied (this should be 0 during a WOT pull).
  3. AF sens 1 ratio AFR – The current air fuel ratio from the stock Subaru sensor **this sensor does not read correctly below ~12:1 afr. Any value richer than 12:1 should be checked against the wide band o2 sensor. In the case there is no wide band present as in this log you should see the value maxed out at 11.15 during high RPM/heavy load/boost over 10psi.
  4. Manifold abs. pressure- Current manifold absolute pressure (post throttle body)
  5. Calc. Load- Calculated load value used by the ECU to determine fuel/ignition map look up values.
  6. Closed loop SW- closed loop/open loop switch *off means the ECU is operating in open loop*
  7. Dyn. Adv. Mult (DAM) – This is a VERY important value to monitor. A healthy happy Subaru should hold the max DAM value at all times. (value of 1 for new Subarus and 16 for older ECU models.) This means if you see the DAM value drop below the max value the ECU is hearing knock and is pulling timing. **If you see the DAM value drop this is something you should discuss with your tuner right away.** Some tuners will set the initial DAM value low letting the ECU increase the DAM slowly, this is ok but it is FAR better and safer to start the DAM initial value at its max and fully tune the ignition map/trims. 
  8. Dynamic advance (degree) – ignition timing value currently being added to ignition base map, Formula: DAM/max DAM value * current dynamic advance ignition map value. 
  9. FB knock – Feedback Knock correction. *this number should remain at 0, a negative # means the ECU pulled timing.
  10. FK learn – Fine knock learning *this number should remain at 0 95% of the time. This is the ECU’s first attempt to lower engine noise/knock. Even a well tuned engine will sometimes show a VERY small negative value here but 95% of the time it should remain at 0 as in this log.
  11. Ignition timing- Total ignition timing.
  12. Inj, duty – Injector Duty cycle *this value should not go over ~90%*
  13. SD VE (Commanded) – Volumetric efficiency point commanded by ECU.
  14. Commanded Fuel Final – final commanded AFR value by ECU after all fuel trims are factored in
  15. RPM – Engine speed
  16. Throttle – Throttle position
  17. Intake temp – Intake air temp
  18. Waste gate duty – current waste gate duty cycle.
  19. AP info – This should show the name of the current map/calibration used for the data log

Custom sensor logging set up and wiring for Subaru Cobb AccessPort: https://cobbtuning.atlassian.net/wiki/display/PRS/Subaru+Custom+Sensor+Logging

If you need a custom Pro Tune or E-tune for your Cobb AP click here, custom base map or your current tune dialed in check out E-tune options and feel free to contact us any time.

Don’t have a Cobb AccessPort? No problem we tune just about everything, click here to check out our tuning services for more details.

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