Anyone know?

They are some EXPENSIVE little buggers!!

I'm still chasing my spark knock on regular gasoline.....

These little engines DO NOT need 93 octane fuel!!!!!

 

There is a series of posts on ford-trucks that tell the tale of how to substitute some electronics for the FFV sensor. If you search for FFV or flex-fuel, you might find the series. The inventor was considering producing and selling some sort of kit to make failed sensors work for the normal mix of gasoline:alcohol found on the road. It did defeat the actual flex fuel capability. I believe it ended up being a resistor of a given value that was substituted.
tom

 

the signal from the flex fuel sensor is a square wave whose frequency varies with the alcohol content percentage. I have a substitute on my 2000 that puts out a fixed signal for 10% alcohol. been a few years since I installed it, I'm thinking it was made by ts electronics or something like that.
it is not a resistor, its a timing signal generator.
test it with a frequency counter.

Perry

 

Probably a 555 timer.. a pretty simple and compact circuit. Fixed resistors can be substituted for the potentiometer once the target frequency is known. 555 Variable Frequency Square Wave Generator | Electronic Circuits

As for testing the FFV you need a scanner of some type, FORScan is a free diagnostics SW package that runs on a laptop with a simple ELM327 interface.