My 2011 Silverado is Flex Fuel and I'm curious about running it on E85. If I understand it correctly, there is an alcohol sensor somewhere in the fuel system so it knows when it gets a supply of E85; and the control mosule switches to the appropriate tables. Is this correct?

Other questions:

Does this sensor measure the alcohol content and the ECU adjusts tune accordingly? In other words, is the system able to accommodate inconsistent blends that might be encountered; or say there's 1/8 tank gasoline remaining and the tank is filled with E85, or something.

Can methanol - as opposed to ethanol - be blended with gasoline at 85/15 and run without any other changes?

Anything else anyone can contribute?

Just learning about it.

 

Ok, answering a couple of my own questions, some Google searching turned this up:
https://cecas.clemson.edu/cvel/auto/sensors/flex-fuel-sensor.html

It's not vehicle specific, but does answer most of the questio s I asked.

 

It's been a while, but I think the GMT900s actually used a physical sensor some years and a "virtual" sensor in later years. Not sure which year they switched. They went back to a physical sensor in the GenV engine in 2014. My 2013 used the "virtual" sensor.

But yes, the correct term is "Flex Fuel" meaning is will adapt to whatever the E% content is at.

Don't know nothing about adding meth.

 

Yeah 2011 will be virtual, so you'll need to purchase a sensor, install it, wire it and program the calibration to use the real sensor. Like 4-5 tables need new data put in so they will function with the sensor.

The newer trucks are weird though, 2014 has a sensor while 2015+ it all depends on how the truck was equipped. Seen several files that not factory with a sensor.

 

Interesting. So how does the pre-14 'virtual sensor' work? Does it use the O2 sensors or something? Seems like this would be "too late" and result in chasing the proper mixture but never getting there...

If it's Flex Fuel it's supposed to be E85 capable as is, so why do I need to add the physical sensor? Are you saying the virtual version doesn't work well; the physical version is an improvement?

 

I switched my gmt900 (07 nnbs) to flex fuel. It has an e38 computer which has a pin available on the ecm that takes the signal from the Continental alcohol sensor which was installed on the return line. Sensor measures alcohol content and outputs a frequency into the ecm which then uses the appropriate tables. If you are going boosted, I would just add the sensor and not rely upon the "virtual" ability. The Continental sensors are relatively cheap and you can get pigtails for the wiring.

 

Thanks for the detailed info.

 

The virtual sensor uses the fuel trims to figure out the alcohol content.

That's a small info blurb about how it kinda works.

The real sensor is much faster and far more accurate.

 

Thank you for that explanation. Now that I have read that it is crystal clear why the addition of a fuel sensor is needed.