Earlier this year we were able to release COBB Custom Features for the 2008+ WRX and STI. The most sought-after feature in that release was the ability to create true Flex Fuel calibrations for your car. Gone are the days of having to switch calibrations every time you visit the gas pump. The Flex Fuel calibration simply utilizes the actual ethanol content of the fuel to appropriately blend an assortment of related tables. Today, we are extremely excited to announce that COBB Custom Features, including Flex Fuel, are now available for the 2015-2017 USDM Subaru WRX!
What are the benefits of Flex Fuel ?
The dyno sheet above gives a good idea of how taking advantage of higher ethanol contents can result in increasing power and torque. The car used for these pulls is utilizing our Stage 2+ Big SF Power Package (Non-Resonated J-Pipe) with the addition of our Flex Fuel Ethanol Sensor Kit and Flex Fuel tuning strategy. As you can see, power improves significantly by simply increasing ethanol concentration.
- Red indicates 15% Ethanol
- Blue indicates 48% Ethanol
- Green indicates 74% Ethanol
After dialing our 2015 WRX in on the dyno, we took it to San Antonio Raceway (1/4 Mile) to get some real world results. As you can see in the video, by simply increasing the ethanol content from E10 (93 octane) to E73 we saw the 1/4 Mile trap speeds increase by over 6 MPH!! This, again, is with a car that is utilizing our COBB Stage 2+ Big SF Power Package (Non-Resonated J-Pipe) and Flex Fuel Ethanol Sensor Kit. That’s it, no other performance modifications.
The first step in setting your vehicle up for Flex Fuel is to install the COBB Flex Fuel Ethanol Sensor Kit. This is the easiest to use and most sophisticated Flex Fuel kit on the market. Utilizing OEM fuel and electronic connectors, the Ethanol Sensor Kit measures the ethanol content of fuel being fed to the motor. That data is then converted into a signal that the ECU can use for adjusting calibrations and to be displayed on a custom Accessport monitor.
- Utilized by COBB Flex Fuel Tables, Retains All Factory Compensations
- Custom DTC Error Reporting for Water in Fuel
- Billet Aluminum Converter Case
- Coated Aluminum Sensor Mount
- OEM Quality Electrical & Fuel Line Connectors
**Requires custom tuning. CLICK HERE to find nearest COBB Shop or Protuner for a custom Flex Fuel tune.**
For more information, see the product page HERE.
COBB Custom Features + Accesstuner Updates
The updates below are immediately available for both Subaru Accesstuner and Accesstuner Pro. Software versions are below.
- Subaru Accesstuner : 126.96.36.199-13565
- Subaru Accesstuner Pro : 188.8.131.52-13570
- 2015 USDM WRX MT
- 2016 USDM WRX MT
- 2017 USDM WRX MT
Ethanol Content Delay System
The Subaru DIT WRX fuel system is a return-less system. This means it may take up to a few minutes for fuel that has flowed passed the Ethanol Content Sensor to actually reach the combustion chamber. In that time period, there can be a significant discrepancy between the fuel being injected and the ethanol content being reported to the ECU.
This component of the COBB Flex Fuel tuning strategy is truly what sets it apart from other DIT Flex Fuel tuning solutions. The ECDS system prevents Ethanol Final changes from the time it activates until the Exit Threshold based on fuel mass injected is achieved. This prevents large changes in engine operation based on ethanol sensor readings from occurring before fuel at the sensor reaches the combustion chamber.
While not a significant concern on return fuel systems because fuel is almost always circulating through the rails, this is critical on DIT’s return-less fuel system when fuel ethanol content changes dramatically. For example, when adding pump E85 to a nearly-empty tank of 93 octane fuel (E10).
For more information on this system, see the Subaru Flex Fuel Tuning Guide.
Additional Accesstuner Updates
Non-Zero Ethanol Sensor DTC Delay Defaults Added for GR CCF ECUs
The default values for the ethanol high and low DTC delays have been changed from 10 to 30 (the equivalent of about 1 second). This prevents an ethanol sensor DTC (C0BB1 or C0BB2) if the ethanol voltage is out of range for a period of time less than the delay. This avoids setting a DTC and CEL for what may just be brief, intermittent noise. However, the CCF features will still lock Ethanol Final value the instant the out of range voltage is seen so there will be no adverse effects from the intermittent noise. This feature has been added to all existing CCF ECUs.
- Ethanol Sensor DTC Delay (Low)(C0BB1 DTC)
- Ethanol Sensor DTC Delay (High)(C0BB2 DTC)
Map Compare Feature Updates
There are three key updates to the Accesstuner Map Compare Feature for this release that should greatly improve workflow for Protuners.
DTC and Toggle Comparison
Compare to Other Stock
Import Comparison Differences
Simplify map maintenance with the new “Import” table feature. Simply load a comparison map(s) and select the tables you with to import by using the table selector.
Revert Active Table to Stock
Fuel System Considerations
As with other DIT platforms (i.e. VW, BMW, Mazda), the fuel pumps in Subaru DIT vehicles are not designed for ethanol use beyond 10-15%. That said, ethanol levels between 15-30% are generally well tolerated. Those comfortable with mild risk can run ~E30 and enjoy improved knock resistance, charge air cooling, and a mild improvement in engine power potential. While you can’t get E30 at the pump, pumping a combination of E0/E10 gas and E85 in an appropriate ratio will allow blending of a near E30 mixture in your tank.
On DIT platforms not set up for flex fuel from the factory, at greater than 30% concentration, ethanol has caused oscillating fuel pressure first, progressing to loss of fuel pressure, high pressure fuel pump damage, even making the vehicle inoperable in some cases. Sudden loss of fuel pressure can cause sudden loss of acceleration, stalling, which can reduce braking performance and steering control. Long story short, while the power potential is very attractive, use of high ethanol content fuel is at your own risk.
COBB has performed internal testing in multiple geographic locations with different fuel sources in addition to compiling data from COBB retail shops, our Protuner network, and customers. Results varied significantly. Some users ran several tanks of E85 in a row without issue while some experienced serious loss of fuel pressure in as little as 1-2 tanks of fuel.
We suggest monitoring fuel pressure for oscillations. After having fuel pressure issues, some users were able to flush the HPFP (high pressure fuel pump) out with low ethanol gasoline and get it to operate normally again while others had to replace the whole pump assembly before they could safely drive the car again. After replacing the pump some users experienced repeat failures if they continued to run E85 fuel.