2000 ranger flex fuel sensor

[Campbell]

how do you diagnose a flex fuel sensor

 

[pjtoledo]

you can use Forscan (and an adapter) to get info from the computer. it can tell what the output of the FF sensor is.
there are other OBDII readers and diagnostic tools that work too.

or, you can go the technical route and use an ocilloscope to monitor the FF output via tapping the wires.
it's a square wave signal whose frequency changes with the alcohol content.

those FF sensors are expensive!! Flex Fuel replicators are available on Ebay and other places, I used one for several years.

the first time my FF sensor failed it basically flooded the engine so bad it wouldn't run.