Speeduino has the ability to modify fuel and ignition settings based on the ethanol content of the fuel being used, a practice typically known as flex fuelling. A flex fuel sensor is installed in the feed or return fuel lines and a signal wire is used as an input on the Speeduino board.
As ethanol is less energy dense, but also has a higher equivalent octane rating, adjustments to the fuel load and ignition timing are required.
Speeduino uses any of the standard GM/Continental Flex fuel sensors that are widely available and were used across a wide range of vehicles. These were available in 3 different units, all of which are functionally identical, with the main difference being only the physical size and connector. The part numbers for these are:
All 3 use a variant of the Delphi GT150 series connector. You can use a generic GT150 connector, but you will have to clip off 2 tabs from the side of the sensor.
Part numbers :
Alternatively, there is a GM part for a harness connector, part number 13352241: http://www.gmpartsdirect.com/oe-gm/13352241
All units are wired identically and have markings on the housing indicating what each pin is for (12v, ground and signal) Speeduino boards v0.3.5+ and v0.4.3+ have an input location on their proto areas that the signal wire can be directly connected to.
On boards earlier to these, you will need to add a pullup resistor of between 2k and 3.5k Ohm. Recommended value is 3.3k, however any resistor in this range will work. Note that this is a relatively strict range, more generic values such as 1k or 10k DO NOT WORK with these sensors.