How to: Cobb AccessPort Data Logging for Subaru WRX & STI

Cobb AP Data Logging, record, review and analyze like a Pro

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 “health 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 are all VERY important parts of owning any turbo Subaru. This article will walk you through exactly what you need to do and need to know when data logging your STI or WRX using the Cobb AP. 

2008 WRX E-tune for new engine break in, low boost:

• Supertech pistons (stock bore)
• Manley H beam rods
• ACL bearings
• BC cams
• ID1050x injectors
• Cobb EBCS
• Cobb V3 AccessPort 
• WRX E-tune
• Stock location upgraded turbo 20g and top mount IC (slightly larger than stock).

DIY Cobb AP data log video: This video will walk you through step by step how to record a data log using your Cobb AP. Once you have the data log recorded you can move on to reviewing the log. 

Reviewing Cobb AP Data Logs (Spread Sheet)

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.
Those looking to graph you Cobb AP data logs as well as use your data logs for virtual Dyno results keep reading for the PRO solution to viewing your data logs.

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.

Reviewing Cobb AP data logs like a PRO

Once you have successfully taken a data log using your Cobb AP you can open and review the log file. While using a spread sheet to view the data log is OK we highly recommend using Mega Log Viewer. This program will let you graph all your Cobb AP logs visually as well as apply math’s and even run virtual dyno tests for TQ and HP readings all from your data logs! 

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

Engine Break-in Tune EJ25 WRX:

Fully Built STI with ETS 6870 Turbo kit (low boost pump gas)

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

If you need a custom E-tune, base map or your current tune dialed in check out full list of E-tune options for the FA20 WRX and EJ20, EJ25 STI/wrx. If you have any tuning related questions feel free to comment below or contact us any time. If you need any other parts to complete your build before it’s ready for tuning let us know and we can help you save some extra $$$. We match any price online plus we give package discounts to customers who get their parts and tuning through Brewed Motorsports or FFrides.com 

Not using a Cobb AccessPort for tuning? No problem we tune just about everything, click here to check out our tuning services for more details on all the ECU’s we support. 

Best Subaru STI & WRX Modifications:

If you want your STI or WRX to make the most reliable power possible check out these Subaru specific articles for the for hands down The Best STI Mods and The Best WRX Mods. For those limited to pump gas but want to make e85/race gas power check out the 101S Octane booster. When blended with 91 octane pump gas the 101S can easily be used to bump octane up to 93-95 octane range, this is IDEAL for any turbo Subaru limited to 91 octane at the local gas pump.