Cranks but no start

When I turn key on I hear fuel pump, fuel pressure at test port on fuel rail is 40 psi. Snapping blue spark at coil wire, weak yellow spark at secondary spark plug wires, tried a couple of wires. Rotor turns. Set at TDC, rotor points to #1. Replace plugs, wires, cap and rotor. Still no start. Checked ignition control module at Auto Zone checked good. Replaced distributor with reman distributor w/pick up coil. Still no start. What am I missing. This truck is a snow plow truck at a hospital. Had salt dispenser in bed. Total rust bucket. Sat most of time. 28,000 mi.