I normally just smell it.

Or look at it. We’re all spinning our wheels until the TS (troll starter?) elaborates.

 

There was an "IQ Fuel" project to develop a sensor that used infrared transmission properties to identify fuel types and quality. Most of the references to it are about 10 years old. Presumably flex-fuel vehicles have some way to detect what kind of fuel is in the tank.

 

Presumably flex-fuel vehicles have some way to detect what kind of fuel is in the tank.

My initial thought was that you are wrong. It was my understanding that a flex fuel vehicle is not much different than an ordinary vehicle, with some changes to the rubber compounds to resist the ethanol and the ECU makes gradual adjustments for fuel type based on feedback from the normal sensors that all modern vehicles have (O2 sensors, knock sensors, etc). But you said it, so I looked it up, and you are correct. I may have been correct in the early days of flex fuel but not any more. The sensors they use are called fuel composition sensors. Here's a dumbed-down almost useless explanation of how they work:

"Clemson Vehicular Electronics Laboratory: Flex Fuel Sensors" https://cecas.clemson.edu/cvel/auto/sensors/flex-fuel-sensor.html

 

My initial thought was that you are wrong. It was my understanding that a flex fuel vehicle is not much different than an ordinary vehicle, with some changes to the rubber compounds to resist the ethanol and the ECU makes gradual adjustments for fuel type based on feedback from the normal sensors that all modern vehicles have (O2 sensors, knock sensors, etc). But you said it, so I looked it up, and you are correct. I may have been correct in the early days of flex fuel but not any more. The sensors they use are called fuel composition sensors. Here's a dumbed-down almost useless explanation of how they work:

"Clemson Vehicular Electronics Laboratory: Flex Fuel Sensors" https://cecas.clemson.edu/cvel/auto/sensors/flex-fuel-sensor.html

The sensor in FlexFuel vehicles was going to be my first suggestion in this thread but after looking into the technology, I think (it's been a while) I decided it wouldn't really work for what the TS asked for.

But I think the TS was a troll and did indeed get just what he wanted.