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E-85 Flex Fuel Conversion Overview

5 Aug 2019 11:01 AM | Anonymous


The flex fuel sensor measures the ethanol-gasoline ratio of the fuel being used in a flexible fuel vehicle. Flexible fuel vehicles can be operated with a blend of ethanol and gasoline, up to 85 percent ethanol. In order to adjust the ignition timing and the fuel quantity to be injected, the engine management system requires information about the percentage of ethanol in the fuel.

The flex fuel sensor uses quick-connect style fuel connections, an incoming fuel connection, and an outgoing fuel connection. All fuel passes through the flex fuel sensor before continuing on to the fuel rail. The flex fuel sensor measures the fuel alcohol content, and sends an electrical signal to the engine control module (ECM) to indicate ethanol percentage.

The flex fuel sensor has a three-wire electrical harness connector. The three wires provide a ground circuit, a power source, and a signal output to the ECM. The power source is battery positive voltage and the ground circuit connects to an engine ground. The signal circuit carries the ethanol percentage via a frequency signal.

Alcohol content information is supplied to the ECM from the fuel composition sensor. The fuel composition sensor has a battery positive circuit, a signal circuit, and a ground circuit. The fuel composition sensor uses a microprocessor inside the sensor to measure the ethanol percentage and changes the output signal accordingly. The signal circuit carries the ethanol percentage via the frequency signal. The ECM provides an internal pull up to 5 V on the signal circuit, and the fuel composition sensor pulls the 5 V to ground in pulses. The normal range of operating frequency is between 50–150 Hz. The microprocessor inside the sensor is capable of a certain amount of self-diagnosis. An output frequency between 180 Hz and 190 Hz indicates that the fuel is contaminated.
GM vehicles will automatically detect and calibrate to run gasoline, e85 or any blend of these two fuels. Why run e85 in your vehicle? Ethanol (or e85) is a remarkable fuel source!

  • 105 octane rating – in most cases better than 110 octane race gas
  •  Engine will run cooler with a 27 percent reduction in heat compared to premium gas
  •  Extreme tolerance to detonation, some naturally aspirated engines are able to run up to +15:1 compression ratio.
  • ETs are less affected by atmospheric changes
  •  Does not leave carbon deposits like gas, so maintenance is reduced across the board
  • Not corrosive like methanol
  • 35% more energy than methanol
  • Performance is comparable to best race gas at a fraction of the cost
  • e85 is offered at a growing number of gas stations:
  • e85 is a renewable fuel source that is also environmentally friendly

If you are already running E85 or researching the possibility of running E85, you should be aware that the ethanol content in any gallon of "E85" you get from the pump will vary from 70%-85% ethanol depending on the time of year and what part of the country you are from.  It typically runs around 75-80% in the winter months and late spring and 85% during the summer and early Fall. Of course sometimes it even varies by the station that sells E-85!

If your car has been tuned specifically for 85% ethanol content - you have to either adjust your tune or mix your own.  Both Ignite Racing Fuels and VP Racing Fuels sells 100% Ethanol (actually only ~ 98%) in 55 gallon drums and also probably in smaller sized drums.  You can even purchase 55 gallon drums of pure E-85 and E-90 if you don't want to mix the 100% ethanol with pump premium fuel.

Here’s a quick reference for how much of each grade to mix with 100% ethanol to make 10 gallons of E85:

5gal 70% + 5gal 100% = 10gal 85%
6gal 75% + 4gal 100% = 10gal 85%
7.5gal 80% + 2.5gal 100% = 10gal 85%

What's your ethanol percentage?
The ethanol content of E85 fuel can vary from 60% to 92% ethanol. A fill up with E85 can drastically change the mix of fuel in your vehicle. For performance drivers determining actual ethanol content of E85 is essential to maximizing an engine tune and horsepower.

Why know your ethanol percentage?
E85 has the equivalent octane rating of 105 octane gasoline. Higher octane fuel is more resistant to knock allowing for more aggressive ignition timing, higher compression and increased engine power over gasoline itself.
Zeitronix had released an ethanol content analyzer gauge which is a new ECA gauge they have produced in both blue and red LED displays. Currently only available in the rectangular gauge, their digital electronic display is designed to show the viewer the precise percentage of ethanol contained in their fuel mix.

Not only does this gauge work on standard gasoline which contains ethanol contect of up to 10% in today's fuel, but it also will also work with standard E85 stations, E98 mixes, home brewed mixes of 100% and anything in between.

It is a standard practice for Ethanol stations to periodically change the exact mix of the fuel being brought from the supply tankers available at the pump. On the Ethanol pumps you will notice a sticker indicating a minimum rating of 70% Ethanol content, much like the 10% content labels on standard gasoline pumps today.

Aside from slight variances in actual ethanol content, in many locations there is a "winter blend" major change in the content at E85 stations that take it down to the minimum 70%. They do this for improved cold start performance of the engine.

Problem is if you have been custom tuned to the edge of performance at 85% ethanol and all of a sudden got less ethanol and more gasoline, your car would no longer be tuned for the fuel content you had originally been set up to use.

On flex fuel N/A cars, these changes in content can be handled by the front O2 sensor which can adjust the fuel trims automatically. However on a high performance turbocharged engine with 20lbs+ of boost pressure, a 15% change in alcohol content can have a serious impact on performance and octane level.

So if you are considering an E-85 flex fuel conversion, contact us and we will answer any questions you might have including providing you a turn-key quote which includes parts, labor and tuning.

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