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It sure seems like there's still a completely dead cylinder. Ignoring the testing that you've done already, I'd suspect a bad part in the high voltage path - plug wires, coil wire, cap, rotor. Have you tried misting it with a water spray bottle in the dark to see if you can see any arcing?
In your video, the cable from the distributor sensor is clipped to the high-voltage cable from the coil. There's a chance that this is causing electrical noise in the disti sensor. As a test, remove the cable clip and separate those cables by a couple inches.
do the spark plugs work correctly in another car
Have you tried setting it on fire!?
That's a good spray pattern. Makes the correct sound, too. Is the spark color nice and white on the plug when you tested spark? I'm wondering if it's fouling the plug so you lose the cylinder. Even a slightly weak spark in that cylinder could cause the plug to foul and not fire. That is barring any mechanical issue it's got hidden from you.
I think that since we have a complicated problem it must not be tested the spray of a single injector only but also that all the sprays of all the injectors are even.
Furthermore I discourage to spray the fuel into air, the risk of fire is very high. It is sufficiente to insert each injector into a transparent plastic bottle to avoid fire hazards and to compare all the sprays together.
While I have no good ideas to try, as a lot had been suggested already, I have been thinking about this.
Before it started to behave so badly. How did the plugs look like if you would have stopped during the fist mile with the misfire?
Could you perform an compression test right away after the first mile?
Would it still misfire for the first mile with a few drops of in the cylinder, to see if bad rings are the culprit? Not sure how fast oil is washed away.
Have you tested coolant for HC with contrast liquid?
Checked for sticking valves or something crazy like that? Bad valve spring, when things have been moving for some time and have warmed up they might be free to move..
Just some ideas.
I thought that the white "smoke" might very well be unignited gas. That's why I wanted you to smell it. I think you, also, initially had a leaking head gasket/cracked head issue, which is now, hopefully, behind you.
I also think that you picked up an injector issue, post head gasket, possibly even to a degree at the same time you were having the head gasket issue.
Could be why the missing cylinder moved on you. I'd recommend doing another video of injector testing, but test all 4 injectors. It's best to have all four spray patterns to really compare. It makes a weaker pattern stand out more obviously, and also to compare opening pressure differences.
Also you really don't want all that fuel from that injector, that isn't being tested to just be washing out that #3? cylinder.
Try applying just a little rotational twist, at an angle, to the tool, while pulling up the metering plate, not enough to change the adjustment, but to just help it keep tensioned in the allen head, so it doesn't pull out of the allen head, Also, if you can get a parts wash can with a long spray straw to spray down into the opening of the allen head, to make sure the allen head doesn't have crud built up in there, keeping you from getting your tool all the way down in there.
It's not so important about what your pattern looks like at partial through full throttle, that's not where your injector spray pattern is going to be, when cranking to start it up, also your engine runs fine, other than the misfire, above idle.
What's most likely happening is that, if it is an injector issue, the spray pattern may not be atomizing at initial opening, and shooting out unburnable streams of fuel, or just dribbles out fuel, which is fouling out the spark plug before the engine even gets started. At which point that spark plug is not going to fire until it becomes dry. The same thing that happens when you flood a carbureted engine by pumping the gas pedal too many times on start up. Also I'd recommend swapping #1, an#2 injectors with hoses attached again, on start up, just as an additional diag test.