Mis fire on #4 cylinder

1. Engine runs fine but way over due for new spark plugs
2. Changed plugs & #4 starts misfireing intermitently within first 20 miles at all RPM's
3. Removed #4 plug and it had moisture on exterior of plug but not on the fireing end. Moisture smells a little like engine coolant but not positive that is what it is.
4. Reinstalled plug, with compressed air dried area, reinstalled lead with a nonconductive silicone grease to help seal out moisture.
5. Misfire continued and is getting gradually worse over time. Pulled plug again and found again moisture on exterior of plug but not the fireing end. The electrode end is clean and dry and shows normal usage.

6. Now What????

What kind of vehicle are you working on tim , and which engine does it have? Do you have a distributor with wires, or coil packs? The moisture could be getting in/on the coil pack, or dist cap and wires, depending on which you have.

What year is it?It is a bad coil if it has the coil on plug ignition,known for eating them.It could be plug wires if it has coils packs

It is a 1998 f150 with a 4.6 L
It has wires and not the coils on the lead ends.

Hook up an extra plug or spark tester to that wire and see if it sparks. If not, then the coil may be dead there. If so, I would suspect an injector.