Flex Fuel for Honda

Running E85 as an alternative to race gas in nothing new in the racing community. I have been running my supercharged Acura Integra on E85 for two years now, and have helped many others make the switch. E85 is high octane, chemically contains oxygen, requires more energy to vaporize (meaning it reduces cylinder temperatures) and is much less expensive than high octane race fuel. Most people see a significant increase in power output (with proper tuning) when switching from pump 91 octane gas to E85. Sounds all good right? Well there are some down sides to running E85. Contrary to popular belief  E85 is no more corrosive than the pump gas we put in our cars, which is E10, but, E85 does require roughly 30% more fuel ( say good-bye to good MPG). E85 is also more susceptible to being contaminated by water, so leaving it in a fuel system for a long period of time can and probably will introduce rust. Depending on the weather where you live, E85 can range from E70 to E85 from winter to summer months. Lower ethanol content allows for easier starting in cold months. Here we only have E85 roughly 2 months out of the year. This means the tune on a car will appear to fluctuate as the ethanol content of the fuel fluctuates with the changing blends.  This can be a very big deal on a car that has been tuned on E85 to make maximum power, but now is running E70 because of a blend change. E85 is also not as readily available as traditional gasoline  Where I live we have one pump at one station where we can get E85.

Many SUVs and trucks sold today can run E85; how do these vehicles combat the change in blend problems and the availability problems? The answer is Flex Fuel. A Flex Fuel system automatically adjusts the vehicles tune based on changes in ethanol content. This means a person can fill up on E85 today, and midway through the week decide to put a half tank of regular unleaded fuel in and not worry about what will happen with the mixture of the fuels.


Why does this all matter? I have been slowly working on a flex fuel solution for any aftermarket tuning system that can make fuel and ignition timing changes based on a 0-5v input to the ecu. Neptune's tuning software, which is what I use for hondas, now has what they are calling, "sensor adjustments"

This adjustment uses a 0-5v input to make changes to fuel, timing, and boost solenoid duty cycle based on voltage. This could be used for Flex Fuel, if only the sensors would output a 0-5v signal, which they do not. Using the sensor adjustment, a turbo car could be setup to make lots of boost and power when the fuel lines had E85 in them, then be set to turn down the boost and power when traditional pump gas was being used.

Today I have a working prototype board that uses a flex fuel sensor in the return line of the fuel system on my Integra to output a 0-5v signal back to the Neptune ecu. This excites me, Flex Fuel is a reality for my car. Now I can have the benefits of E85, but still have the option of driving my car on a long road trip where E85 may not be available, or filling up at any gas station if necessary;  I also no longer need to worry about blends of E85 as my tune adjusts all the settings when I fill up with E70 and turns everything back up when I fill up with E85.

For me this is great news, I felt the need to share and I hope that others out there feel the same. Any tuning system that can utilize a 0-5v input to make adjustments to the tune would be able to make the change to Flex Fuel. Depending on interest, there is potential for a production unit, even the possibly for a DIY project with instructions for those who want to tackel that task.

Video: car is running at idel, and the sensor is reading 82-83% ethanol, manuel tests showed roughly 80-85% ethanol. Lower left hand gauge is the Ethanol% the video quality on here is not great.