AEM 30-71XX Infinity Stand-Alone Programmable Engine Mangement System Full Manual - Manual (Page 243)

Tuning Guide 237
© 2014 AEM Performance Electronics
Flex Fuel Tuning
Flex Fuel is a fuel mixture of ethanol (alcohol) and gasoline. It is typically made from corn (or
sugar cane) and is used for cleaner emissions, higher octane, and is less expensive per volume.
However, ethanol's energy density is lower so gas mileage is compromised. But from a
performance standpoint, the extra fuel lowers exhaust gas temperatures which is a benefit.
Furthermore, ethanol has a higher latent heat of vaporization compared to gasoline so air charge
cooling is further improved. When burning ethanol, the fuel tuning should be based on a oxygen
sensor because reading spark plugs is much more challenging as the color is not as evident.
Flex Fuel Composition
Gasoline and ethanol have different compositions: Gasoline: H1.65C, Ethanol: C2H5OH. Ethanol
has oxygen as part of its structure (gasoline does not) and is often referred to as "oxygenated
gasoline". Because of this, the stoichiometry of the two fuels are drastically different.
Flex Fuel Stoichiometry
Gasoline stoichiometry: 14.68 AFR
"E85" stoichiometry: 9.87 AFR
Ethanol stoichiometry: 9.00 AFR
Flex Fuel Content
Most gas stations label their flex fuel as E85 (85% ethanol and 15% gasoline). However, this can
be very misleading. Most cold climates use a winter blend which is E70. In order to determine the
proper amount of blend that is being used at any given time, a FCS (fuel composition sensor)
must be used.
Flex Fuel Sensor
Below is a list of part numbers associated with the GM FCS (Fuel Composition Sensor) unit:
GM 12570260, Fuel Composition Sensor, Quantity 1
Delphi 12146121, Connector, Quantity 1
Delphi 12048074, Terminals, Quantity 3
Delphi 12052845, TPA, Quantity 1
Delphi 15324973, Cable Seal, Quantity 3