Congratulations on your purchase of the COBB Tuning Flex Fuel kit! The following instructions will assist you through the installation process. Please read them BEFORE beginning the install to familiarize yourself with the steps and tools needed. If you feel you cannot properly perform this installation, we HIGHLY recommend you take the vehicle to a qualified and experienced automotive technician.
IMPORTANT! Installing this kit will require custom tuning or utilizing an appropriate Stage Power Package map if you have a matching mechanical configuration. Please consult with COBB or an authorized ProTuner in your area.
Part List
Tools Needed
Important! Before removing your fuel line, make sure to discharge existing fuel pressure from the system. Failure to do so can result in fire, property damage, and/or death!
The COBB Flex Fuel Kit is designed to work in harmony with the COBB Fuel Pressure Regulator Kit (STI only), as well as the fuel pressure sensor kit. These instructions assume you have already followed their instructions and properly installed both.
Installation of COBB Flex Fuel Kit Hoses
The COBB Flex Fuel Sensor installs between the manifold side fuel line connector and the regulator. In our example, we're using the COBB fuel pressure regulator, so we'll be installing the sensor on our return line before the new regulator hose. Our Flex Fuel Sensor and/or Fuel Pressure sensor do not restrict fuel flow and will not cause any hindrances. It's mandatory that you install either sensor pre-regulator to ensure accurate readings. The flow of fuel is as such:
Instructions are similar for WRX, however, WRX users need to scroll to the "Amendment for WRX" section for a WRX specific connections.
The COBB Flex Fuel Module is designed to be bolted to the inter-cooler support bracket and plugged into the COBB Ethanol Sensor, in-line with the factory Rear O2 sensor and Tumble Generator Valve (TGV).
The Rear O2 connector obtains 12V power and does not alter the O2 sensor signal going to the ECU. The TGV connection allows the motor signals to pass through for those still using the factory TGV's, however, the feedback normally used to check TGV position is used to transmit Ethanol content data to the ECU (Engine Control Unit).
Mounting location may vary by customer/ installer preference, however, it is recommended to seal any unused connections from water intrusion, ideally by using the proper connector mate and using plugs to seal the mating connector.
While the assembly procedure is similar for the WRX, the following images show how the fuel lines are routed differently. The Flex Fuel Sensor will go in-line of the return line, and the Fuel Pressure Sensor will go in-line of the feed line (if purchased).
Regulator side:
The WRX Uses the lower connection (pictured) for a return - connect the barbed hose (no quick connect) here
Manifold side:
The upper quick connect on the manifold side is used for either the fuel pressure kit, if purchased
The bottom connection here is the return line (shown bending down to the fuse box), which will be used for the ethanol content sensor (in-line of the return flow)
Below is a completed configuration using R&D components:
Ethanol Sensor Input Selection = TGV Left
Sensor calibration:
0.5 V = 0% Ethanol
4.5 V = 100% Ethanol
COBB Product Install Instructions for Subaru Vehicles
Main Installation Instruction Repository for Subaru Parts
Calibration Map Notes for Subaru Vehicles
Link to Subaru Map Notes to see what map you should be on given the parts you've added