3.7L Atlas V6 (Vortec 3700): Chevrolet Colorado / Hummer H3 / GM

This is a supplementary guide to help you install your eFlexFuel E85 kit installation on the Vortech 3700 engine in the 2007-2012 Chevrolet Colorado and 2007-2010 Hummer H3.

• 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 by clicking here.
• 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.

If you come across any errors in this document, please let us know. Additional photos, feedback, and suggestions to make this installation guide easier for others are greatly appreciated and can be sent to support@eflexfuel.com. Anyone who sends photos that are used to update this guide will receive a free eFlex Merch Pack.

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

You will need to remove the intake manifold to access all injectors. This is known to be an in-depth task. You can search Google and YouTube for some great tips and guidance. Watch these videos for reference https://www.youtube.com/watch?v=v6cVFIMLLeQ & https://www.youtube.com/watch?v=JrGJLeNMWoc and also refer to the instructions below.

1. Remove the throttle body.
2. Remove the battery box.
3. Remove the oil level indicator and tube.
4. Disconnect the brake booster hose (6) from the brake booster.
5. Disconnect the engine wiring harness electrical connector (3) from the manifold absolute pressure (MAP) sensor.
6. Disconnect the engine wiring harness retainer (4) from the intake manifold (5).
7. Disconnect the positive crankcase ventilation (PCV) dirty air tube (2) from the camshaft cover.
8. Remove the generator.

9. Disconnect the engine wiring harness retainer (1) from the intake manifold (2).

10. Remove the upper 2 bolts securing the engine wiring harness bracket to the intake manifold.

11. Raise and support the vehicle only high enough to access the remaining components through the wheelhouse.

12. Remove the left front wheel.

13. Remove the left front wheelhouse liner.

14. Disconnect the following wiring harness retainers from the engine wiring harness bracket:

• The battery cable
• The engine (4, 6)
• The MAP sensor (5)
​

15. Remove the remaining engine wiring harness bracket lower bolt. Remove the bracket from the engine compartment through the wheelhouse opening.

16. Remove the intake manifold bolts.

17. Lower the vehicle.

18. Remove the intake manifold from the cylinder head.

19. Mask off the open ports to the cylinder head, in order to prevent foreign objects from entering the engine.

After removing the intake manifold, you can access the fuel rail and injectors.

2. Ethanol Sensor Installation

Ethanol Sensor Mounting

• The ethanol sensor will mount between the feed line and fuel rail.
• Unplug the feed line from the rail.
• The original line is pressurized, be careful when removing.
• Use safety glasses and a rag to soak up the excess fuel and be cautious of anything that may ignite the fuel.

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.

 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.

 Securing the Wiring Harness

• Any unused length of the harness should be bundled and run alongside the fuel rail or as far away as possible from the ignition coils or leads. Zip tie this in place.
• Make sure any slack is safely secured so there is no risk of touching moving or hot parts.
• Check surrounding components that only move sometimes, such as windshield wipers, steering components, etc.
• Due to the nature of electrical components, a clean install also has a positive effect on the signal strength and minimizes electrical interference.

Still have questions? We are here to help!

• First, try visiting the Customer Support Center at support.eflexfuel.com and searching and/or browsing our troubleshooting guides. Most answers are there!
• Email us at support@eflexfuel.com
• Call us Mon-Fri between 9AM-5PM PT at 833-539-3835

Thank you for joining the #E85Movement!

We hope you make the most of your additional torque and horsepower. We invite you to follow us on Facebook (@eFlexFuelUSA) and Instagram (@eflexfuel) to join a community of likeminded individuals. Most importantly, have fun and enjoy your drive!