So, i decided to change the plugs on my G35 since its at 93K miles and the previous owner never done so. This is a 04 G35 coupe with 6MT
Now i get a misfire on cylinder 4. Only cylinder 4.
Things i have done so far:

Check for intake leaks - this would have no effect because even without a MAF and air box car runs like crap, i can disconnect cylinder 4 plug and engine runs the same, if i disconnect any other coil plug, engine runs worse; limp mode or not. Regardless, I checked all hoses, connections related to intake. No dice. Besides, if it was an intake leak, it would be an intermittent issue that would come back and go away. Simply cant be an intake leak.

Swap coils from a working cylinder - no effect, does same thing

Change plugs from a working cylinder - nope.

Check all grounds - nope

Check the injectors - all injectors work properly, fuel does get into the cylinder as there is a strong fuel smell from cylinder 4 and the fact that when i pull the plug from cylinder 4, its slightly damp with fuel. No the injector does not flood the cylinder, I've pulled the rail and checked for that as well.

Check the coil plug on cylinder 4 - i get the correct readings, when compared to other plugs from working cylinders.

Here what is most elusive about this issue. If i get a plug and coil, put the plug into the coil and hook it up the cylinder 4 harness plug, there is a spark. If same coil and plug goes into the cylinder, it refuses to fire.

I even checked compression on cylinder 4, 165Psi.

I don't have my old plugs, i threw em away so cant test that. I checked for gap, .044. I even bought another brand of plug to try, nope. Car is stock.

So, suggestions? Any takers? I'm beyond mad right now.

 

I had mixed plugs from cylinder 6 and 4.
Lol. Problem solved.