Flexible Fuel Sensor: Description and Operation

Flexible Fuel (FF) Sensor:

PURPOSE
The Flexible Fuel (FF) sensor detects the dielectric constant, the conductivity, and the temperature of the fuel being fed to the engine. This information calculates the percentage of Methanol present in the fuel blend being used. The Methanol and fuel temperature information is transferred to the Powertrain Control Module (PCM) in the form of a frequency and pulse width modulated signal. The PCM uses this information to calculate the correct air/fuel ratio and spark advance for the fuel blend being used.

OPERATION
The frequency signal represents the percent of Methanol in the fuel blend. The transfer function is linear. A 50 Hz signal represents 0% Methanol and a 150 Hz signal represents 100% Methanol.

The pulse width signal represents the fuel temperature. The transfer function is linear. A 1 millisecond positive pulse width represents a temperature of -40° C and a 5 millisecond positive pulse width represents a fuel temperature of 95° C.

The signal nominally switches between 0 and 5 volts.

NOTE: The output from this sensor does not have to be accurate as the closed loop feedback provided by the Heated Oxygen Sensor (HO2S) corrects errors in the calculated air/fuel ratio.