#4 plug misses...

[joe_db]

There is a lot you can do.
Here is my scope connected to the #1 plug lead:

You can see the plug fire, the points close, and the plug fire again.
You can use a FLIR camera to analyze the engine.

You can put a timing light on the ignition to dial in the advance.
You also can do a lot with nothing but your ears and eyes.
LOOK at the plugs. I posted a chart to interpret what you see. Also look for soot traces up the insulator, I had one leaking combustion gas through the plug.
LISTEN to the engine. Run it with a bit of load and pull the plug wires one at a time. The RPM drop and engine roughness should be about the same for every plug. If one pull does nothing, that cylinder isn't even firing. If 2 aren't firing, you may have swapped plug wires and have them in the wrong order.
FEEL them. A quick light touch on the plug boot will give you a rough temperature check. If one is significantly colder than the rest, you have an issue.

[Sam]

Also a few years back DR N Dutton suggested purchasing an inexpensive "induction" pen light that you hold next to a plug wire and it lights with every firing for that wire. Does not measure "quality" of spark but does indicate very quickly that you do have spark. Remember it being about $5 on ebay.

[ndutton]

We've had a couple of convenient spark tester schemes. The one Sam refers to is from Lisle, available on Amazon, eBay, Walmart and others:



Then there was the spare spark plug mount in the alternator/lifting eye bracket. Pull the plug wire in question, put it on the test plug and crank: