Subaru – Data Logging Overview

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It’s never a bad idea to examine what’s going on behind the scenes to determine how well your car is running.  This is especially important anytime tuning changes or hard part modifications are made to your vehicle.  Completing a data log and reviewing the results can help troubleshoot or identify any issues that may be present.  At first glance, the amount of monitors and the sheer volume of data can be a bit overwhelming.  The following is a general guide covering some key parameters on your COBB supported Subaru.

Every Accessport is automatically setup with a default log list.  This list of parameters will help troubleshoot the most common issues of the specific vehicle with which the Accessport is used. Here is a link to the Full Monitor List which defines each monitor.  That’s quite a few!   Having an in-depth knowledge of how your engine works, and the affects added modifications have, allows troubleshooting of more complex issues.  Luckily, an in depth knowledge isn’t required for a basic wellness check.  Below are some of the key monitors that can help determine you engine’s overall health.  If you’re unsure of how to gather the data from your vehicle, check out COBB U Episode 17 covering how to data log.

After you’ve recorded your data log, it will be time to examine the results.


Top Monitor list

There are some key monitors within the default list that can help gauge whether there are any issues present.  There are some differences in newer model year (2015+) WRXs, but for EJ equipped Subarus, these monitors include: A/F Learning 1, Boost, DAM, Fine Knock Learning, and Feedback Knock.  Let’s take a look at each of these monitors individually in more detail.

A/F Learning 1

This monitor shows a percentage correction for fueling.  Positive numbers indicate that fuel is being added.  Negative numbers indicate that fuel is being removed.  The closer to zero the better, but generally, the acceptable range would be +/- 10%.

Negative corrections beyond 10% mean the ECU is pulling lots of fuel.  This would most likely be due to a leak in the intake tract.  Other potential issues could be a bad MAF sensor, failing o2 sensor, or you may have a map flashed that is not designed for your intake or injectors.

Positive corrections beyond 10% mean the ECU is adding lots of fuel.  There are several potential culprits in this situation.  A failing fuel pump, dirty fuel injectors, or bad MAF or o2 sensors would all be good starting points to address the problem.  As always, having parts installed not designed to work with the map you are running could also cause high positive fuel trims.

MAF and o2 sensors are typically on their way out after ~100k miles.  If yours are still original, and you have mileage beyond 100k, replacing these sensors would be recommended.  Definitely replace the front o2 if engine or turbo damage has ever occurred.  When it comes to these critical sensors, always use OEM parts from a Subaru dealer or a re-seller of genuine Subaru OEM parts.

Boost

Boost is the manifold absolute pressure minus the current barometric pressure measured in PSI (or bar if you prefer to configure the units in metric).  Positive numbers indicate the intake manifold’s boost pressure.  Negative numbers indicate the car is in vacuum.  You should consult the map notes to determine the target boost value for your specific map.  STIs have different boost targets within the same map depending on the drive mode selected.  Note that this target range will only be achieved during wide open throttle through mid-range RPM with load on the engine.  It is normal for boost to taper down as you approach redline.  We typically recommend a third gear pull to gather this data.  You can then compare the boost values in your data log to the target in the map notes to determine whether you are under/overboosting.  Many vehicles have off the shelf high wastegate and low wastegate maps that address vehicles under/overboosting.  Higher altitudes and any mechanical issues should be considered when concluding whether you are under/overboosting.  More details on these maps and these issues can be found here.

The monitor can also help determine whether a vacuum leak exists.  Actual vacuum at idle will vary from car to car (it is typically around -10 for these Subarus) but if you’re only seeing -2 at idle, it’s safe to say you likely have a vacuum leak somewhere.  This will negatively impact how the car runs and could prevent you from reaching target boost.

DAM

The DAM, or Dynamic Advance Multiplier, adjusts the vehicle’s overall timing based on its current and historic knock readings.  This parameter is useful in determining the overall health of the vehicle.

For the 02-05 WRX this value will range from 0-16 and for other EJ model Subarus it will range from 0-1.  The starting point after a flash will vary depending on the model and tune but you always want the DAM to “learn” up to its maximum value.

This value will reset after an map reflash, an ECU reset, or a battery disconnect.  But, if you see it drop under any other circumstance, you could have a potential knock issue.  The following parameters can help determine if that is the case.

Fine Knock Learning

Fine Knock learning, sometimes abbreviated FKL, is a learned correction that the ECU uses to make tweaks to timing.  If FKL hits extreme values, the ECU will consider modifying the DAM.  Corrections start as a multiple of -1.4, and are learned away in increments of .35.  With that in mind, if you see a -1.05 correction, knock is not currently occurring and timing is already being added back in.

Feedback Knock Correction

Feedback Knock Correction is an instant response the ECU applies to timing based on a knock event occurring.  An initial value is typically -1.4 or -2 depending on the ECU.  You may see this on occasion especially at low loads.  This is common and will happen on a completely stock vehicle.  If you see these Feedback Knock corrections of -4 or higher at wide open throttle, that is cause for concern and should be investigated.  More details for interpreting knock on the Subaru platform can be found here.


If everything checks out with the above monitors, chances are, everything is running just fine.  If you do come across anything concerning our customer service team is only a phone call or email away!  We can be reached at 866-922-3059 or at support@cobbtuning.com.


COMMENTS
Daniel Stig on September 24, 2017 says:

Hi,

In A/F Learning 1 where you refer to potential bad o2 sensor due to +/- corrections beyond 8%, do you mean both up (front?) and downstream o2 sensors?

Also, for my 2005 WRX is the Denso 234-9011 Air Fuel Ratio Sensor the same thing as the front o2 sensor?

Thx!

Reply
    Kyle
    Kyle on September 25, 2017 says:

    Hi Daniel,

    Any issues caused by a bad o2 sensor would likely be the front o2. o2 sensor is typically interchangeable with AFR sensor. Based on the amazon reviews, that looks to be the correct part number for your application but I’d recommend confirming with a dealer just in case.

    Kyle@COBB

    Reply