The problem is corn requires a lot of fossil fuel energy input, mostly in the form of fertiliser. The net energy output is only around 1.3 so an acre of corn produces maybe 400 gallons of gasoline equivalent output requires 300 gallons of gasoline equivalent in energy inputs.

Ethanol from sugarcane makes a lot more sense. Corn ethanol is just a wasteful subsidy for farmers paid for by drivers.

https://en.wikipedia.org/wiki/Ethanol_fuel_energy_balance