This is a post from
http://www.gminsidenews.com/forums/f13/ ... tem-28729/Subject; Virtual Flex Fuel Sensing.
What we need is an engine that can run on any mixture of ethanol and gasoline (or just straight gasoline). That is where the Chevrolet Impala Flex Fuel system comes into the game. In the past, GM had some small trucks and SUVs that could operate on different mixtures of ethanol-based fuels. These vehicles used a fuel sensor in the fuel line that signalled the computer how much ethanol was present in the fuel; the computer would add or subtract the amount of additional fuel required. Now, the Impala flex fuel system can perform this analysis without using any additional sensors.
GM has developed a Virtual Flex Fuel Sensor (V-FFS) software program that calculates the ethanol content in the fuel, instead of using a sensor to measure it. When the fuel level in the tank increases as the vehicle is refueled, the computer recalculates the percentage of ethanol in the fuel and automatically changes the air/fuel ratio. To do this, the computer temporarily stops the operation of other emission systems and monitors the oxygen sensors to determine ethanol content. The test is done several times until calculations remain stable. This can take several minutes when the engine is idling, but much less time at higher fuel flow rates.
There are no visible indications on the Impala that it is flex fuel-capable and there is no extra equipment. If your Impala has the 3.5-litre V6 engine and the eighth digit of the serial number is a "K", then it is ready for E85. It even drives the same. When operating on E85, it does use a little more fuel, but green house gases are reduced dramatically. There is a slightly sweet smell to the exhaust and you have the satisfaction of knowing you are running on a renewable fuel resource.
Most of the Impalas sold in the United States will be flex fuel compatible. In Canada, about half of the vehicles will have this capability. GM is offering them at no additional cost compared to traditional gasoline-powered vehicles. They can be operated on gasoline now, but will be ready for E85 when it becomes available, as it surely will in the future. I don't know if the Impala will be the chicken or the egg, but it does come before the fuel and it is ready for the future. Also, here is a PowerPoint presentation that covers Inference Strategy or Virtual Flex Fuel Sensing strategies.
The paper suggests that the Inference Flex Fuel strategies will displace the Flex Fuel Sensor.
http://www.siucautomotive.com/presentat ... exfuel.pdfSo, the research suggests that both Ford and General Motors have their own tried and tested VFFS systems.
I have one of Matt's Flex Fuel Tunes (in H6), and so does No.2 Son (in NA 2.5i), and they are working a treat.
Plus the many, many American cars running a version of the VFFS technology.