Trouble in starting 1999 Expedition, 4.6L, 8 cylinder

I am having trouble starting my 1999 Expedition, 4.6L, 8 cylinders, 97,000 miles. The starter is turning the crankshaft, but the engine will not start. I already checked fuel pressure at the gage inlet in the fuel rail line (located on top of valve covers); fuel pressure is 40 psi during cranking. Also, I checked for sparking at the spark plug wires. I removed the boots from the spark plugs and observed sparking during cranking. Everything is sparking correctly, and therefore I believe that the ignition coils (two) and spark plug wires are functioning correctly.

I would appreicate any advice as to where I should target my troubleshooting. Thank you kindly,

Tim

Have you checked for injector pulse?