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Ready to convert your car eco friendly?

Installing your eFlexFuel E85 conversion kit is pretty straightforward. We've included a set of complete installation instructions below, so you can see what's involved.

Installation guide (auto)

1. Before you begin installation

  • Before you start, please take a moment to plan the installation. Locate the fuel line, the fuel injectors and a place for the ground wire and control unit. Plan how to wire the eFlexFuel system so that it's not placed next to any moving parts, excessive heat or high voltage components.
  • The engine needs to be maintained and in normal operating condition with no engine warning lights showing
  • Make sure that the vehicle's engine is tuned for gasoline. Using a flex fuel or an E85 tune with eFlexFuel can cause a serious engine failure.
  • Do not fill up with E85 ethanol before installation.
  • Make sure that the engine is cooled down.
  • Remove the keys from the ignition and do not open the doors during the installation.
Package Contents
  1. Control unit
  2. Ethanol sensor
  3. Fuel line quick connectors
  4. Fuel hose
  5. Hose clamps
  6. Main wiring harness for 1-4 cylinders
  7. Extension wires for 5-8 cylinders
  8. Male connectors
  9. Fuel line disconnect tool
  10. Bypass Module
  11. Extra analog wire (eFlexPro only)
Tools Required
  • Eye protection & gloves
  • Multimeter
  • Basic tools
  • Cutting- and Needle nose pliers
  • Cleaning rags
eFlexFuel kit
I have verified the following before moving on to the next phase
  • The engine is adequately maintained and in normal working condition with no engine warning lights showing.
  • The product package contains everything that is listed under the package contents.
  • I have located the fuel injectors and planned where to place the ethanol sensor, ground wire and the control unit.
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2. Installation of ethanol sensor

Before You Begin
  1. Block or secure the vehicle and confirm that there are no combustion sources near or around the vehicle and work area.
  2. The ethanol sensor needs to be installed to a location free from moving parts, high temperatures and high voltage components
  3. The fuel hose should be as straight as possible. Avoid tight bends. The minimum radius for a bend is 3"
  4. Use quick connectors that are provided with the kit for installing the ethanol sensor.
  5. Do not use solvents when installing the fuel hose
  6. Lubricate the quick connector seals with clean engine oil before installation.
  7. The ethanol sensor can be installed to either the incoming fuel pressure line or the return line. In most engines we recommend installing to the incoming pressure line.
Parts Being Installed and Warnings
  1. Ethanol sensor
  2. Ethanol sensor connector
  3. Fuel hose and hose clamps
  4. Fuel line quick connector
Installation Figure F

Use quick connectors when installing the ethanol sensor! Fire/explosion risk if not used!


Fire/explosion risk from gasoline & vapors.

The fuel line is disconnected in this step. Improper installation or routing may result in spilled fuel. Assure that the engine is cold, and that no electrical or other ignition sources are within or adjacent to the working area. Use rags to remove any spilt fuel and dispose in an appropriate sealed container.


Fuel system is pressurized. Use cleaning rags to avoid fuel spill. On top of this use appropriate personal protection equipment (at least eye protection and gloves).

Installation Step-by-Step
  1. Disconnect the original fuel line.
    • If the original fuel line connectors cannot be opened by hand, use the fuel line disconnect tool provided with the eFlexFuel kit.
    • Use rags to protect the engine from fuel spills.
  2. Prepare the new fuel line assembly with the ethanol sensor
    • You can use the original fuel line or replace it entirely with the fuel line provided with the eFlexFuel kit.
    • Use quick connectors with all joints and lubricate them with engine oil.
  3. Install the new fuel line assembly.
    • Make sure to use the quick connectors and the hose clamps provided with the eFlexFuel kit.
    • Make sure that the connectors are locked and the hose clamps are tightened properly.
I have verified the following before moving on to the next phase
  • The ethanol sensor is properly fastened with the quick connectors included in the accessories kit.
  • There are no tight bends in the fuel line.
  • No solvents were used during the installation.
  • The ethanol sensor is not within close proximity of high voltage engine components such as ignition coils.
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3. Preparing the Wiring Harness

Before You Begin
  • The wiring harness connects the eFlexFuel® control unit to the ethanol sensor and the fuel injectors. This enables the eFlexFuel control unit to control the fuel injection in real-time.
  • For 5-8 cylinder engines first the extension wires need to be connected to the wiring harness so that the number of injector wires matches the number of cylinders.
  • In order to install the wiring harness to the engine, the polarity of the engine's fuel injector connectors is measured with a multimeter.
  • Then the male connectors are plugged to the wiring harness' terminal couples. Finally, the wiring harness is connected to the fuel injectors and the ground wire, temperature sensor, ethanol sensor and control unit are connected to the wiring harness
The Wiring Harness
  1. Row connector (Plugs into the control unit)
  2. Ground wire
  3. Temperature sensor (Red/Orange tip)
  4. Ethanol sensor connector
  5. Female fuel injector connectors (Plugs into the fuel injector)
  6. Terminal couples (Inserted to the male connectors and then plugged on to the vehicle's wiring harness)
  7. Male connectors (Plugs into the terminal couples and then the vehicle's wiring harness' wires)
  8. Four extension connectors (For 5-8 cylinders)
  9. Four extension wires (For 5-8 cylinders, plugs into the extension connectors)
Wiring Harness
The Fuel Rail and The Fuel Injectors
  1. Fuel rail
  2. Fuel injectors
  3. Engine's original fuel injectors connectors
Fuel rail and fuel injectors

Locate the fuel injectors. If there are engine covers or an intake manifold on the way, remove them to gain access to the injectors

Disconnect the fuel injector connectors and compare them to the wiring harness provided with the eFlexFuel® kit to make sure they match.

If the fuel injector connectors do not match please contact the place of purchase or eFlexFuel® customer service at support.eflexfuel.com/hc/en-us or 1-833-539-3835

Preparing the Wiring Harness

Correct installation of the wiring harness is crucial for the operation of the eFlexFuel® system. For this the wiring harness needs to be prepared by installing the male connectors to the terminal couples and for 5 to 8 cylinder engines the extension wires are added to the main wiring harness.

For 5-8 cylinder engines the first step is to add extension wires to the main wiring harness that comes with injector wires up to 4 cylinders. Take the extension wires and install them to the main wiring harness' extension connectors. The number of injector wires needs to match the number of cylinders. If the engine has only 4 cylinders, please move on to the next phase.

Measuring the Fuel Injector Polarities

The fuel injector connectors' polarities are measured from the engine's wiring harness' wires that come from the engine control unit and plug to the fuel injectors. This allows to plug in the male connectors to the eFlexFuel® wiring harness' terminals the right way.

Use the multimeter's continuity function (audible "beep"-mode) to determine how the engine's wiring harness' terminals are connected to each other. Please follow these instructions:

  1. Make sure that the multimeter is on the continuity mode. You can do this by tapping the probes together to hear a beep
  2. Start by taking two of the engine's wiring harness' injector connectors (e.g. cylinder 1 & 2). First, let's find out which terminals are connected to each other. These will be the positive terminals (+12V).
  3. Place the multimeter's probe to either of the terminals of the female injector connector wire coming from the engine control unit to the first cylinder you're measuring. Then place the other probe to the same side of the another cylinder's injector connetor. If you hear a beep, then these will be the positive terminals. If there's no beep, switch to the other sides of the injector connectors which then should be the positive terminals.
  4. Keep the multimeter's probe in the positive terminal of the female injector connector that was measured first from the engine's wiring harness. Then with the other probe go through all the connectors of the other cylinders to make sure which side is positive (beeps). If you have a V6 or a V8 engine please start from step 2. with the other cylinder bank.
  5. Write down which sides of the fuel injector connectors' terminals are positive. This information is required next.

Installing the fuel injector connectors properly is crucial for the operation of the eFlexFuel system. Failure to use a multimeter and follow these instructions can result in damages to the engine and the eFlexFuel® system.

measuring polarity positivemeasuring polarity negative
Connecting the Male Connectors to the eFlexFuel® Wiring Harness

The wires of the eFlexFuel® wiring harness can be connected in any order to the fuel injectors. Each of the wiring harness' wires has the female fuel injector connector and two terminals that the male connectors will be installed to. They are pairs that need to be plugged in to the same cylinder

Check which way the male connector plugs into the vehicle's female fuel injector connector. Insert the eFlexFuel® harness' terminal with the red wire to the side of the male connector that plugs to the positive side of the female fuel injector connector of the vehicle's wiring harness (which was measured in the previous part). Insert both terminals to the male connectors and pull them until you hear them click. Make sure the terminals are the right way around in the male connectors.


The vehicle's wiring harness' plus (+) wire can be any color.


Make sure that the terminal pins are inserted all the way to the male connectors. Use pliers to pull them if needed

  1. Terminal couples
  2. Male connector
  3. Vehicle's wiring harness' female injector connectors
connecting male connectors

Make sure that the terminals lock in to the male connector. Test this by gently pulling the wires after installing them.

Once all the male connectors are installed to the eFlexFuel® wiring harness, it is ready to be installed

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4. Wiring Harness Installation

Installing the Wiring Harness to the Fuel Injectors
  1. Fuel injector male connector
  2. eFlexFuel® wiring harness female connector
  3. eFlexFuel® wiring harness male connector
  4. Vehicle's wiring harness female connector
Wiring Harness installation

Make sure that the terminal pins are inserted all the way to the male connectors. Use pliers to pull them if needed

First, connect the eFlexFuel® wiring harness male connectors (3) to the vehicle's wiring harness injector wires (4) that were disconnected earlier.

Second, connect the female connectors (2) to the fuel injectors (1).

Placing the Temperature Sensor

The temperature sensor is placed within close proximity of the engine block so it can sense the temperature of the engine accurately.

The temperature sensor measures the engine temperature that is used for adjusting the cold start enrichment. Please note that its temperature readings can differ from the engine coolant or the engine oil temperature.


Do not place the temperature sensor within close proximity of the exhaust manifold.

Connecting the Ground Wire

Ground the eFlexFuel® system by connecting the ground wire to the negative terminal of the vehicle's battery or to an unpainted surface on the engine or the chassis.


Make sure that the ground wire is connected properly. eFlexFuel® system does not work without decent ground connection.

Connecting the Ethanol Sensor

Connect the wiring harness' ethanol sensor wire to the ethanol sensor. The connector should click when it's connected.

Installing the Control Unit
  1. Find a location for the control unit within the engine bay. Preferably close to the cabin.
  2. Make sure that the control unit is not exposed to excessive heat or moisture. Additionally make sure that the control unit is not touching any moving parts and is not placed close to any high voltage wires or components.
  3. Make sure that the pins of the control unit are straight before connecting the wiring harness. Don't use excessive force!
eFlexPro® only - Connecting the eFlexPro® Sensor Wires

The eFlexPro® features two analog wires that can be connected to the engine's OEM sensors or add-on sensors such as wideband lambda.

Please find separate instructions for this from the eFlexPro® manual. You can also download the manual for the eFlexTuner® tuning software and eFlexPro®: eflexfuel.com/us/eflextuner

I have verified the following before moving on to the next phase
  • The polarity of the fuel injector connectors has been verified with a multimeter and the male connectors have been installed to the eFlexFuel wiring harness accordingly.
  • The eFlexFuel® system is grounded appropriately.
  • The eFlexFuel wiring harness has been connected to each fuel injector and to the vehicle's wiring harness.
  • The temperature sensor is placed within close proximity of the engine block.
  • The ethanol sensor and control unit wires have been connected and are not routed close to any high voltage components.

If the engine is running fine and the eFlexApp® connects to the eFlexFuel® system, you can now fill up with E85, gasoline or any blend of ethanol and gasoline.

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5. Finalizing the Installation

Securing the Wiring Harness
  1. Make sure that the ethanol sensor, the control unit and the wiring harness are not within close proximity of high voltage engine components.
  2. Make sure that the eFlexFuel wiring harness is wired loose enough to compensate for engine movement and that it doesn't touch any moving or very hot components such as the exhaust manifold.
  3. To finalize the installation use zip ties to arrange the wiring in a desired way.

Do not place the temperature sensor within close proximity of the exhaust manifold.

To fully benefit your eFlexFuel system download and install the eFlexApp.
eFlexApp logoiOS store icon Google Play Store icon
First Start-up

The installation is now complete and it is time for the first start-up.

  1. Turn on the ignition couple of times without starting the engine. After this, start the engine.
  2. The engine should run normally. However since the fuel line can beempty after installing the ethanol sensor, the initial start-up might take a little longer.
  3. Download and install eFlexApp® to your smartphone and connect with it to the eFlexFuel® device. Make sure that the fuel ethanol content reading is correct and the home screen shows the right amount of cylinders active.
  4. If the engine doesn't start of idles poorly, verify that the fuel injector polarities were measured correctly and the connectors were plugged in properly.
  5. If the eFlexApp® can't connect to the eFlexFuel system and the system is not visible as a bluetooth device, make sure that the ground wire is correctly installed.

If the engine is running fine and the eFlexApp® connects to the eFlexFuel® system, you can now fill up with E85, gasoline or any blend of ethanol and gasoline.


Observe that the fuel line connectors and the fuel line do not leak.

Even a small leak causes a fire hazard.


If the engine doesn't start do not try to start it several times as that can flood the cylinders with fuel. If this happens, let the vehicle sit for an hour to let the cylinders dry out

If after verifying that the injector connectors are plugged in correctly the engine doesn't start or idles poorly please contact our customer service immediately and do not drive the vehicle.

If after verifying that the ground wire has a good ground the app still doesn't connect, do not fill up with higher ethanol blend than E15. Please contact our customer service.

I have verified the following before moving on to the next phase
  • I can connect to the eFlexFuel® system with the eFlexApp® and there are no active fault codes.
  • The app displays that a right amount of cylinders are active.
  • The app displays the engine temperature and ethanol content correctly (usually 0-15%).
  • The engine runs normally and the duty cycle the app displays on idle is less than 5%.
  • If any issues persist after verifying that the fuel injector connectors, the ethanol sensor and the ground wire were installed correctly, contact our customer service.
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6. Driving with the eFlexFuel® System


eFlexFuel is a fully automatic E85 flex fuel conversion system that lets your engine to run on any mix of E85 ethanol and gasoline. The system detects the fuel blend in real-time and maintains perfect air-to-fuel ratio automatically by controlling the fuel injection. No user input is needed when the fuel blend changes.

However, to fully benefit the eFlexFuel system we recommend using the eFlexApp that is constantly being updated and new features are added. You can download it for free from the App Store or the Google Play store. If you have purchased the eFlexPro system, please download the eFlexTuner tuning software to your PC from our website.

Next you can find useful information about how you can make the most of E85 and flex fuel and how to diagnose possible technical issues.

Cold Weather Use

eFlexFuel features a smart cold start that makes sure that your engine will start even in the coldest conditions. However as ethanol fuel does not evaporate as easily as gasoline, in cold conditions cranking might take longer with E85.

To ensure smooth starts in cold temperatures (Colder than 40 °F) we recommend taking the following steps:

  • Use an engine block heater, whenever possible.
  • Fill up with some gasoline (at least 1/10th of the fuel tank) to decrease the amount of ethanol in the fuel.
  • Make sure that the engine is well maintained and, in particular, the ignition components and spark plugs are in normal working condition.
  • Avoid long cranking. We recommend short cranking cycles (2-3 seconds) and adequate pauses in between attempts (5-8 seconds). This helps ethanol to evaporate in the cylinders before attempting to start the engine again.
  • eFlexPlus and eFlexPro come with an adjustable cold start feature that is accessible from the eFlexApp. This will allow you to configure the cold start specifically for your vehicle, if needed.
Maintaining a Vehicle Equipped with eFlexFuel®

When driving with eFlexFuel® and E85 ethanol fuel you can still follow the regular maintenance schedule recommended by the manufacturer of your vehicle. We recommend ensuring that, in particular, the following components are in normal working condition:

  • Spark plugs: The replacement interval recommended by the manufacturer is usually appropriate.
  • Fuel filter (if applicable): Replacement preferably every 30,000 miles.
  • Engine oil and oil filter: Always use the oil recommended by the vehicle manufacturer with SN classification. If the oil change interval is 10,000 miles or less, it is sufficient. If the oil change interval is 20,000 miles or 24 months, it is recommended that engine oils are changed at least once a year or after 12,000 miles.
  • Fuel pump: If the vehicle has done over 125,000 miles with the same fuel pump, its performance may have deteriorated. Ethanol needs to be injected more than gasoline and, thus, the condition of the fuel pump is crucial. As the fuel pump is a component that wears out, it should be replaced when needed. Based on our experiences, we recommend pumps from reputable manufacturers.

Besides the mileage and the age of the vehicle, the circumstances in which it has been used and the way it has been driven has a great impact on the durability and maintenance needs. For instance, if the vehicle is driven for only short distances with a cold engine the maintenance intervals should be shorter no matter what fuel is used.

Filling Up and Fuel Consumption

The eFlexFuel® system enables your engine to run on E85, gas or any blend of ethanol and gasoline. This means that you can fill up with gasoline, E15, E30, E50 or E85 in any ratio and the system will automatically optimize your engine. You can monitor the fuel blend with the eFlexApp.

E85 can have 51% to 83% of ethanol in it. The more ethanol in the fuel the more the engine will consume. The increase in fuel consumption isn't linear meaning that with lower ethanol blends like E50 the increase is usually only 5% to 10% but with pure E85 the increase is usually 25% to 30%.

For best possible savings on fuel costs we recommend using fuel blends between E40 to E60. For the best possible performance we recommend using fuel blends with ethanol content above E60.

Please note that the range display in the trip computer won't recognize the change in fuel consumption with higher ethanol blends.

Engine Tuning and Modifications with eFlexFuel®

eFlexFuel® is a piggyback system that controls the fuel injection to optimize the air-to-fuel ratio on any fuel blend. For this reason eFlexFuel cannot be used in engines that are already flex fuel or have an E85 tune. eFlexFuel works only in engines that are tuned for gasoline.

If you are installing any modifications that affect the fuel injection (e.g. fuel injectors) or getting the engine control unit tuned with eFlexFuel® installed, the fuel blend being used needs to have less than 20% of ethanol. Engine tuning with eFlexFuel can only be done for gasoline. Tuning for fuel blends with more than 20% of ethanol can only be performed with the eFlexPro® system and eFlexTuner® software.

It is forbidden and pointless to change the timing because the engine control unit will automatically perform timing adjustments when high octane fuel is used.


If engine tuning is performed with the eFlexFuel system installed make sure that the ethanol content in the fuel is less than 20% and the tuning is performed for gasoline only.


To access our technical support portal, visit the following website support.eflexfuel.com/hc/en-us or call our customer service at 1-833-539-3835

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