02-07-2015, 07:13 PM
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Perth WRX Old Skool Cool Dude
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Join Date: Oct 2006
Location: Pub
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Originally Posted by matto20v
How the hell does it do that??
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Found some comments:
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I agree about lambda being lambda no matter which fuel you run - but the calculation to get AFR is where the difference comes in. 1 lambda is 14.76 with gas, but not with ethanol - it is 9.76... Maybe that is how they get the PCM to force into the ethanol tables... If the PCM sees 1 lambda from the O2 sensors, when ethanol is in the tank, it will take more fuel to maintain 1 lambda - maybe that's how it knows...
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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."
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In 2006 GM changed the way ethanol percentage of fuel was calculated by their trucks. This new system was deemed Virtual Flex Fuel System. Instead of using an additional sensor in order to measure ethanol content, the ECM had a software upgrade which allowed it to make this measurement by utilizing the fuel tank pressure sensor and level sensor signals. At a key on event the ECM looks to see if the fuel tank level sensor signals atleast a 2 gallon change from the last key off. If so, the ECM shuts the tank vent solenoid, monitors the fuel level and fuel tank pressure. These readings are applied to a formula which gives an ethanol percentage. The commanded air/fuel ratio is then changed according to ethanol percentage of the fuel.
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__________________
[SIGPIC][/SIGPIC]
Should have bought an STI
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