RE 2001 Ford Explorer 
It has a new battery, coil, and wires in place. The truck will not start below -7 F despite strong cranking; in these temperatures, sound of fuel pump priming is muted or absent.  Upon rewarming, the truck starts briskly and pump sounds return.  No other classic signs of fuel pump failure.  Any ideas that you may have would be hugely appreciated.  Thank you!