Flex fuel

A GM / Continental flex-fuel sensor in the return (or feed) reports ethanol content as a frequency and fuel temperature as a pulse width. Race Core reads that on a digital input and blends between a petrol VE/ignition map and an ethanol map — or applies a multiplier. Either way, the sensor has to be true before you lean on it.

Wiring

• 12 V from protected 12 V out or the main-relay 12 V, fused small.
• Ground to sensor GND.
• Signal (frequency) to a Digital input. Assign that input as flex in TunerStudio.

Tune implications

• Stoich moves: petrol ~14.7, E85 ~9.8. Required fuel and targets must follow ethanol %.
• Ethanol wants more fuel volume and usually more timing, and it is more knock-tolerant. It is also colder (charge cooling) — IAT compensation still matters.
• A sensor that sticks at 0 % on a tank of E85 will lean the engine to death if you let flex drive the blend. Put a sanity range on ethanol % and a fail-safe (assume petrol, or shut down).