Ford Flexible Fuel (FF) Sensor Ethanol Output Chart - Frequency vs % Ethanol

This document is a diagnostic reference chart titled "Flexible Fuel Sensor Ethanol Output," apparently from a Ford service/diagnostic manual (figure reference A24584-A). It instructs the technician to use the chart to determine the corresponding frequency range for a known percentage of ethanol in the fuel, and asks whether the FF (Flexible Fuel) PID is indicating a value between 42 and 145 Hz. The chart plots FF sensor output frequency (Hz, 30-140 on the Y-axis) against ethanol percentage (0%-85% on the X-axis), showing a nominal linear output line with upper and lower tolerance bands. An embedded table lists expected frequency ranges: 0% ethanol = 40-60 Hz, 15% = 50-70 Hz, 25% = 60-80 Hz, 35% = 65-85 Hz, 45% = 75-100 Hz, 55% = 80-105 Hz, 65% = 90-110 Hz, 75% = 95-120 Hz, and 85% = 105-125 Hz. A worked example explains that a fuel mixture known to be 20% ethanol should generate an FF sensor output signal in the range of 55 to 75 Hz. A reader can use this page to verify whether a flexible fuel sensor's output frequency is plausible for the actual ethanol content of the fuel during diagnosis.