ka24de p301 misfire

[mavreix]

Hey all, new here. Been banging my head against the wall on this one, I have the Nissan frontier 2000 ka24de with 210k miles. Got a misfire on 304 after filling up with petrol which switched to 301 and has stayed there since. It is not intermittent misfire seems to be steady and and the spark plug on that cylinder is rather black, like its not sparking the fuel.

Things Ive tried:
New plugs, distributor cap, plug wires, then tested for spark - good on all cylinders.
Fuel filter, fuel is getting to injectors, replaced injectors same result.
Tested for compression 120,125,123,125 dry and engine cold.

Any ideas?

[VStar650CL]

You say it happened after a fillup, are you sure the fuel is any good? What do the rest of the plugs look like?