83 bronco w/EFI won't start

83 ford bronco, 4.9 liter, EFI, AutoTrans.  Replaced plugs, wires, cap, rotor and battery.  40 psi fuel pressure at fuel rail.  Good spark to all plugs,  Injectors are being pulsed and all test good - engine will not start nornally.  I have to use a shot of starting fluid to get it going - then I can start and stop it with no problem - it starts right up normally.  When I let the car stand for several hours the problem is back.  Engine turns over fine and fuel pressure is 40 psi - but no start.  I have replaced the air bypass valve but this had no effect - I really don't know what to do next.  Any suggestions would be very much appreciated. 

Get a fuel sample to see if it is contaminated with water.Also repalace the fuel pump relay.