'94 Ford E350 460 cranks but won't start

Spark at output of distributor to plug wires is ok. When I press the pin in the pressure port on the fuel rail as the engine is cranking, there doesn't seem to be any gas. This vehicle is a motorhome.

One more piece of information: Vehicle running good, never a problem, prospective buyer test drove, 30 minutes, alone, pulled back into my yard, engine idling for about 30 minutes as he and I inspected the outside, I reached in, turned the ignition off, he left, 2 hours later, I hit the starter, for the 1st second the engine tried to fire twice then easy smooth cranking but no start from then on. Could he have put something in the tank? Thanks for any help, Steve.