Introduction - Settings - Wiring

The flex fuel system allows the use of E85 or other ethanol and petroleum blended fuel mixes to be used when a special fuel composition. sensor is fitted. The support is specifically based around the use of a GM flex fuel sensor which outputs a varying frequency signal depending on the fuel composition. This information can then be used to add more fuel and advance timing. Ethanol blends need more fuel volume than unblended fuel and different advance.
The system uses a two-point system (low/high) and interpolates between the values. Settings

Flex fuel sensor - this enables or disables the Flex Fuel system
Sensor port - where the sensor is connected - see the wiring section
Frequency (low) - the sensor output frequency to indicate a low blend condition (typically 50Hz)
Fuel correction (low) - the fuel adjustment at this low frequency (typically 100%)
Timing correction (low) - the timing addition at this low frequency (typically 0.0 degrees)
Frequency (high) - the sensor output frequency to indicate a high blend condition (typically 150Hz)
Fuel correction (high) - the fuel adjustment at this high frequency
Timing correction (high) - the timing addition at this high frequency (+ means advance, - means retard) Wiring

The simplest wiring method is using the 'Flex' input on the MS3X. This allows a direct connection to the fuel composition sensor. (The CPU protection is on the MS3 card itself for this input.)
The DIYer may choose to use the other available inputs 'PE0/JS7' or 'JS11' but these require that you build a protective circuit. Note that the layout shown in the Megamanual is unsafe and offers the CPU no protection.

The sensor connections, looking into the sensor, from left to right, are: