Question: Doc is a scientist right? The DeLorean had a ruptured fuel line and needed gas which, as Doc pointed out, was unavailable at the time. Surely he knew how to distill booze to make ethanol? (There was plenty of whiskey around at the time). I mean, they've used it to power cars in Mexico for ages. Why didn't Doc suggest this?
Bodragon
26th Mar 2018
Back to the Future Part III (1990)
Answer: Putting to the side for a second the possibility that he either did not know how to do this, or simply didn't think of it... a quick Google search says that the entire process to produce ethanol would take about a week. They had about 3 days because they were trying to leave before Doc got killed.
Answer: They did try it. Doc ran the engine with the strongest thing the bartender could find them and it blew out the engine. It takes all the power a heavy car like a DeLorean has to get up to 88 MPH. It wouldn't be able to get that much power running on ethanol, in addition to the damage caused to the engine.
Greg Dwyer