This is a supplementary guide to help you install your eFlexFuel E85 kit installation on the Subaru Impreza EJ253 2.5L. This guide may also be helpful for other vehicles with a similar powertrain.
- This guide should be used in combination with the main Installation and User Guide included with your kit. The main Installation and User Guide can also be accessed here: Manuals
- The instructions in this guide are numbered to correspond with the steps of the main Installation and User Guide.
- There is no single correct way to install the ethanol sensor and control unit. Depending on your engine bay layout and personal preference, your installation may vary from this guide.
Kit components include:
- Vehicle specific harness: Wiring harness to connect this kit to your vehicle.
- Vehicle specific fuel line accessories: Fuel line components to install the Ethanol sensor.
- eFlexFuel Control Unit: The eFlexFuel “brains” / ECU.
- Ethanol Content Sensor: Measures Ethanol % of fuel.
- Bypass Module: A “dummy plug” that can be used in place of your eFlexFuel Control Unit for troubleshooting, NOT an OBD plug. Normal gas (E10) must be in the tank to use the Bypass Module. See the Customer Support Center for more information.
YOU WILL BE DICONNECTING FUEL LINE DURING THIS INSTALLATION – ALLOW THE ENGINE AND COMPONENTS TO FULLY COOL DOWN BEFORE ATTEMPTING INSTALLATION.
1. Pre-Installation
Read all steps and plan for this installation. Not following instructions may lead to a temporarily inoperable vehicle. Review full instructions before beginning and do not skip any steps.
Before You Begin
Remove the top cover and intake to gain access to the fuel rail and fuel injectors.
2. Ethanol Sensor Installation
Ethanol Sensor Mounting
- Disconnect the fuel feed line from the fuel rail. You will build an extension line between the fuel rail and original line with the Ethanol Sensor in-line.
- The original line is pressurized, be careful when removing. Purge the fuel pressure from the Schrader valve (or other proper way) if available.
- Use safety glasses and a rag to soak up the excess fuel and be cautious of anything that may ignite the fuel.
Making the new hose/line:
- Measure appx how long you need the extension line to be.
- Cut the provided fuel hose into two appropriate lengths.
- Attach the ethanol sensor in-line with quick connectors on the sensor and clamps over the fuel line.
- Connect one male and female 8mm quick connector on each end of the newly built line with hose clamps.
⚠️Remember to use hose clamps where rubber hose is used and quick connectors on all connections.
- Use the supplied fuel accessories and build additional line with the Ethanol Sensor. You can make a small loop between the original hose and the fuel rail.
- The sensor can mount facing either direction as it has no flow direction.
- The ethanol sensor and sensor wire should be as far as possible from the coils and ignition leads to prevent electrical interference.
Check that connections are properly tightened. You can prime the fuel pump to look for leaks.
3. Preparing the Wiring Harness
Unplug the OEM wiring harness from the injectors. Be careful not to use too much force on the retaining clip as old plastic can be brittle.
Measuring Fuel Injector Polarities
- This step is crucial! Carefully follow the instructions in the main installation guide and watch this ChrisFix video for further detailed instruction: https://youtu.be/eo2jZjG1XA8?feature=shared&t=1190
- Take your time on this step! An error here will lead to malfunction when you first start the vehicle and can be tedious to correct as you will need to de-pin.
- If you run into issues on this step and polarity may be flipped, visit our Customer Support Center for how to test & de-pin.
👉Check article: How to check polarity of male connectors?
Connecting the Male Connectors to the eFlexFuel Wiring Harness
- Connector pins/terminals may go in both ways but will only lock if inserted in the correct orientation.
- Confirm the pins are locked into place by gently pulling the wire for resistance.
4. Wiring Harness Installation
Placing the Temperature Sensor
- Zip tie or fasten the end of the temp sensor as close to the engine block as possible.
- The purpose of the temp sensor is only to communicate appx engine temperature during startup (e.g. a cold engine on cold start Vs a warmed up engine starting on a cold day).
- The temp sensor enables the eFlex Control Unit to properly calibrate startup fueling but has no effect on regular operation.
Connecting the Ground Wire
- We recommend using the engine block as your main ground, though other primary grounds can also work.
- Do not use a grounding point near ignition components or their leads.
- Good grounding is necessary for proper eFlexFuel functionality. If the device does not turn on or you have Bluetooth issues, and injector polarity is correct, re-check the ground.
Installing the Control Unit
- Find a dry place for the control unit and secure it with an appropriate bolt, zip-ties, high strength double sided tape, or velcro.
- It is important not to put strain on the main connector to the Control Unit. Confirm there is some play/slack when plugging in.
Connecting the Optional eFlexPro 0-5V Analog Input Sensor Wire(s)
- The eFlexPro kit comes with one analog input wire already installed in your harness. This wire is optional and typically only connected to an aftermarket wideband. If unused, simply wrap this wire up neatly.
- This wire has zero impact on the eFlexPro’s performance and is only used for optional datalogging for tuning purposes. For more information on the optional 0-5V Analog Input Sensor Wire(s), please visit the Customer Support Center.