| Ethanol is used to increase the octane in place of the other chemicals that are normally used, so it should still be 89 and the ECU should still detect it as 89.
However, I highly doubt the ECU has any idea what octane you are putting in, it is just a passive response to the slightest early detonation that it corrects for; without driving it hard it never has a reason to know that the gas you put in will detonate earlier. | 
