Still have a miss fire 02 Excursion changed all coil packs and plugs the #3 plug was the only one with black soot on it?

Is the computer code coming up as a misfire or are you actually feeling the misfire when you drive? Make sure all the grounds for the coil packs and engine are solid and clean. Many times there is rust corrosion under the pack or the retaining screws etc, Low compression can feel like a misfire as well. If all items are OK do a compression check to verify its not an issue.

check your modulator under your coil pack might have a bent pins on that coil pack or damage if only those 3/6 coil missing

You said you changed the coil pack and the wires but didn't mention the plugs. Try moving one of the plugs to a different cylinder and see if the miss follows it. It could also be the ignition module. (the thing the coil packs mount to.)

Firing order is 1, 5, 3, 6, 2, 4. Number 1 cylinder is up front. Why would you need the firing order, this engine does not have plug wires, each plug has its own coil pack, each coil pack is controlled by the computer.

Try moving the coil pack from cylinder 1 to another cylinder (swap locations) and see if the same code comes up. If code is different, then coil pack is bad. Other reasons for miss; bad injector, poor compression.
Also, I know you changed plugs already, but always use AC Delco 43-103 plugs on this vehicle.

Check the right wiring diagram connections... 2002 Mercury Cougar 2.0 liter DOHC L4 VIN "3"



Also, I find few diagrams about Igniotn System...

Fig. Engine Ignition, Page 01 (2002, System overview)

Fig. Engine Ignition, Page 02 (2002, Duratec-VE)

Fig. Engine Ignition, Page 03 (2002, ZETEC-VCT)

Hope helps.

Hello there:
Just out of curiosity did you change the ignition controle module this sits under the coil packs that is bolted to the engine This tells the plugs when to fire and it can fire on half of it and have the other half not work this is one of the first things that will fail and give this type of a problem also you may want to check the crankshaft sensoer and the camshaft sensor too.
Ok hope this helps alot
Best regards Mike

Swap the coil pack to another cylinder if it is individual. If not, you should be able to pull the wire away from the plug and hear it fire. If not, you have a bad coil. If so, I would look at doing a compression test and possibly a leak down test.

o2 sensor mixes the difference of fuel and air. i would think u probably need a new coil pack or distributor cap.

Change the coil that's the only thing you did not change and a coil if it's weak will cause a miss fire. You can do a compression check on #3 also. If timing was out the truck would be missing like crazy. Change the coil pack.