Two days after pledging more fuel-efficient vehicles as part of a massive corporate restructuring, Ford Motor Co. is to unveil today an ethanol-powered hybrid test vehicle it says will point to ways to reduce dependence on foreign oil.But the problem is that the flex-fuel Escape Hybrid being unveiled at the Washington Auto Show gets worse fuel economy and doesn't meet the same emissions standards when it runs on ethanol instead of gasoline. These shortcomings highlight two of the challenges ethanol has to overcome before it can make an impact on U.S. energy consumption.