Blackhawks1

Hello. I have a question regarding my 2011 GMC Sierra with the 4.8L engine. I've been trying to run this thing on E-85 for a while with one problem...The truck has that friggin virtual flex fuel sensor instead of a separate physical sensor. It has consistently been way low on the percentages...So of course the truck runs lean and the timing is pulled back. I've drained the tank and filled up with straight 89 octane 100% gasoline. The computer indicated 0% ethanol. So I reset the long term trims and ran the tank empty. I filled up with E85 and and ECM said there was 70% ethanol (I recently purchased HP Tuners). the ethanol content went slowly back down to about 45% after a few tank fulls. I always run the truck at least 10 miles after each fillup. So now I want to add an external sensor and switch it over from the virtual sensor in HP Tunes.I just need to know which pin to go to on the ECM harness to get a signal to the computer. Thanks in advance