1993 Ford F250 sparkplugs

there is a few things that could've happened:
1. You installed spark plugs that were not compatible with the ignition system like platinum plugs,
2. you drop or somebody dropped one of the spark plugs and the diode internally has been ruined, causing the onboard computer to detect a dead cylinder,
3. when removing the spark plug wires you or someone else internally ruined one of them causing the onboard computer to detect a dead cylinder,
4. you or someone else did not properly install the spark plug wires causing the onboard computer to detect a dead cylinder,
reject your work, make sure all the wires or property connected, and feel the spark plug wire to make sure it does not feel broken, check under your hood at the sticker will tell you the spark plugs to use for factory specifications, and don't try to be too smart!