Ok so I bought a 2001 Acura gsr it tuned to run on e85 ok but I don't want to run e85 I wanna go back to gas it has a chipped ecu but I have the original gsr ecu can I just run the e85 out and go back to premium and put the gsr ecu back

 

Better to drain it so you have 0 E85 or syphon all fuel out and run all fuel out the lines. then with the GSR ECU, and stock injectors and stock fuel pump you should be good to go.

One thing you can actually do is depending on the chipped ECU you can have a flex fuel sensor installed and have the engine re tuned. You can then use e85 or 91 without changing anything, the flex fuel sensor changes the tune as it reads the ethanol %. so if you decide to run 91 pump you can mix it with the little bit of e85 you might have left in the tank.