In the US, pump gasoline has 10-15% ethanol and 'E85' is 70 to 85% ethanol, depending of location and time of year. Flex fuel offers the ability to compensate for different fuel ethanol content by using either an ethanol content sensor (S300 V3) or ethanol content analyzer connected to the ECU, which is useful when switching from gasoline to ethanol (and vise verse) or when the E85 ethanol content is seasonally altered.

Analog (Ethanol Content Analyzer)
An ethanol content analyzer converts the output of an ethanol content sensor to an analog voltage proportional to the fuel ethanol content. This analog voltage is then input to the ECU so that it can determine the ethanol content. A suitable ethanol content analyzer is the Zeitronix ECA, which also needs a ethanol content sensor.



Ethanol content analyzer input
Specifies the ECU pin used for the analog input from the ethanol content analyzer.   While only two columns are needed for compensation, 0V and 5V must be present in the table to prevent any problems if the ethanol content analyzer voltage goes outside the normal voltage range.

Digital (s300 v3 only)
With the s300 V3 an ethanol content sensor may be connected directly to the s300 Analog Input 0. No ethanol content analyzer is needed, as the S300 V3 converts the signal from the ethanol content sensor directly. Suitable sensors are GM part numbers 13577394, 13577379, and 13577429. These sensors produce a pulse width modulated output with a variable frequency as well, which ranges from 50 Hz for 0% ethanol to 150Hz for 100% ethanol.



Part numbers:

* Ethanol content sensor GM 13577429 (or use the HA Motorsports E85 ethanol content sensor) The sensor should be installed in the return line from the fuel rail to the fuel tank)
* Plug & pigtail GM 13352241 - not needed if using the HA Motorsports Ethanol Sensor Plug-n-Play Harness for S300
* fuel line to -6 adapter Russell 640863

Sensor wiring:

* 'Vcc' - power (9-18V)
* 'Gnd' - ground [connect to Analog input black wire]
* 'Out' - output to ECU [connect to Analog input red wire]

IMPORTANT: A 2.4 k ohm resistor needs to be wired between Out and Vcc. You can do this anywhere in the wiring between the ECU and sensor. If you are using the HA Motorsports Ethanol Sensor Plug-n-Play Harness, this does not need to be added as it is already built-in to the harness.



Compensation
Both fuel and ignition can be compensated for ethanol content.



Ethanol fuel compensation
Specifies the fuel change based on the ethanol content.  The exact compensation factors should be checked on a dyno with a wideband lambda meter.

Ethanol ignition compensation
Specifies the extra ignition advance based on the ethanol content.

- This content is also provided in the smanager help file: http://www.hondata.com/help/smanager/flex_fuel.htm