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Subaru Accesstuner Tuning Guide Supplement
For 2.4L DIT WRX
December 2022
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Introduction
This document outlines some of the unique engine control unit (ECU) logic and tuning strategies relevant to Subaru's 2.4L DIT WRX. It is not the intention of this document to outline every difference but rather the most notable differences (known to date) that can impact your ability to tune effectively. ECU logic for the 2.4L WRX is very similar to the Subaru Ascent and other DIT models.
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Associated Information
Please refer to the other DIT tuning supplement guides for additional information not described here (where applicable):
Subaru Accesstuner FA24DIT Tuning Supplement
Subaru Accesstuner DIT Tuning Guide Supplement
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Applicable Vehicles
The following Subaru models are applicable to this document:
2022 Subaru WRX 6MT
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Table Descriptions
Besides this document, an additional resource for ECU logic details are the table descriptions shown in the Accesstuner software. These will show up in the lower left corner of the software for the current table that is selected. If not visible, make sure the "Table Description" check box is selected in the View menu. Additionally, the Help menu in the software contains links to documents that list all of these table descriptions as well as all of the data monitor descriptions.
CONTACT US
COBB Authorized Protuners are welcome to contact us with any additional questions/concerns or when in need of troubleshooting assistance.
ECU LOGIC CHANGES
LIMITS
The 2.4L WRX has the following notable limits:
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Ecu Changes
When compared to other FA engine vehicles here are some of the notable differences in operation you can expect
Limits
Boost Reading (Map Sensor Values)
Currently limited to a max of about 61.5 psig at sea level, not including the hardware limit for the factory MAP sensor (which likely is limited to about 24 psig at sea level). We have included the MAP calibration tables to account for the installation of an aftermarket MAP sensor
. Keep in mind if you choose to replace it that the factory MAP sensor
includes an IAT sensor to read air temperature in the manifold.
Boost targets - this is limited Target
Boost targets can go to a
maximum of
~61.5 psig as sea level when the Boost Targets Max. Limit table is raised from its 24 psi limit.
Load limit - load is limited Limit
Limited to just under 4.0 g/rev.
IPW limit - Injector Pulse Width (IPW)
At higher load with richer fuel targets
it’s entirely possible to hit a hard-coded
limit for IPW. This will cause the IPW to go static in the 7.x ms range
which can cause the car to run a different target than intended (leaner than expected
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Requested Torque
Internal values in the ECU cap the requested torque value at 350 N-m
Throttle Map
The 2.4L WRX has some unique changes related to requested torque:
Requested Torque tables
Tables are split by the estimated(calculated) gear position (1st through 6th).
This ecu utilises a new monitor (Gear Position ESTIMATED Req Torque
)which tracks the unique gear position monitor and is used for table switching.
When transitioning between gears, the Requested Torque (Gear Transition) table is used.
Due to internal ECU limits, the maximum Requested Torque value is capped at 350 N-m.
TUNING STRATEGIES
MISCELLANEOUS
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Requested Torque (Gear Transition)
This table is used when the car is transitioning between gears.
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Tuning Strategies
Light Load Knock
During testing, we observed that certain 2022 WRX vehicles can demonstrate very significant knock corrections under very “light duty” conditions. This typically occurs when:We were able to identify a few conditions that can cause this to occur.
The driver reduces throttle input after an acceleration event, but does not lift off of the accelerator entirely, such as when reaching desired speed after leaving a stop light or entering the freeway.
Engine Speed is between 2000 and 3000 RPM
Calculated Load is below 0.5 g/rev
When Some symptoms of this behavior begins:
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can be
Feedback Knock Correction (FBKC) can rapidly increment negative into large absolute values
It will often continue until the driver inputs change, such as increasing or decreasing accelerator position, or until the FBKC value reaches its the maximum negative value allowed by the calibration
It will generally demonstrate itself as large spikes specifically in the “Knock Sensor Noise Level Cylinder 3” monitor
These spikes can be reconciled against the “Knock .
If you keep an eye on the monitor Knock Sensor Noise Level Cylinder 3 you will typically see large spikes in the value.
If you compare these spikes against the Knock Sensor Level Threshold Cylinder 3” monitor
Any time that the Noise Level exceeds the Threshold, an FBKC increment will occur
Our testing indicated that:
The behavior is not consistent across cars but will be easily observed 3 monitor you’ll be able to see that any time the noise level exceeds the threshold, there will be an increment in the FBKC
While this behavior was not seen to be 100% consistent across all vehicles, it will be fairly obvious on the stock (or Stage0) calibration
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if the car does have this issue. We did not see any change (positive or negative) with either higher or lower octane fuel (we tested from 91-96 octane).
It is unlikely that the noise is being generated by legitimate knock events and that it is mechanical/external noise (or
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some other anomaly yet to be uncovered). Many other FA24 vehicles such as the Ascent also can exhibit the noise spikes on Cylinder 3
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but often to a reduced
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level, effectively reducing or
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negating the severity of the issue
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Potential consideration for further investigation:
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The VB WRX 6MT features a mechanical vacuum pump for the braking system and brake booster, as does the Ascent
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This vacuum pump is attached to the passenger side cylinder head and the back of the intake camshaft “behind” Cylinder 3, which could potentially contribute to the excessive noise being detected on that cylinder
we see on the VB WRX.
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It’s possible the mechanical vacuum pump used to provide sufficient vacuum to braking system (via the booster) is the culprit, as on both the 6mt WRX and Ascent, the pump is attached to back of cylinder 3 and run off the camshaft. The VB WRX CVT does not utilize this |
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pump and instead uses an |
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electronic brake booster |
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Mitigating the Light Load Knock.
Our Stage1 maps have a series of small changes included that help mitigate reduce the frequency of these light load knock events, though larger changes may be needed depending on the vehicle and the specific behaviors observed.
IMAGE:
Below you can see a Visual representation of the issue occurring on an in-house test vehicle during early R&D efforts. This is on the stock calibration and a vehicle running 92 octane located in Portland, OR. The 3rd graph shows the noise spikes (red) exceeding the threshold (white), the 2nd graph shows FBKC incrementing downwards when those spikes occur, and the 1st graph shows the benign conditions under which it is occurring (Calculated Load below 0.5 g/rev, APP below 15%, etc.). While not shown in this graph, Cylinders 1, 2 and 4 do not demonstrate the noise spikes at all during this event.
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