I'm not familiar with the JB4 settings, so that's something you'll have to deal with
@Cygnus X-1 straight away. It could be exacerbating the issue but this is only my personal speculation. I don't know what the ECU and JB4 coupled are doing, when it's hot and humid where you live.
I'd have to actually see the insulator ceramic tip inside to determine if it's running lean or rich. The outside of the threads doesn't actually indicate anything except, some possible carbon fouling and a possible rich condition. Otherwise, to much fuel. Some of which is typical of all GDI engines.
However, below are typically what you'd see in either a rich or spot spark plug images. The one on the left denotes
carbon fouled the one on the right is what the plug will look like, if burning correctly.
Honestly your plugs from the
This v is what I need to see;
I presume you're running nothing but premium fuel, correct? I don't care what anyone tells you, don't run anything but premium fuel top tier fuel in this engine. If someone tells you differently, tell them to; "go piss in the wind" so to speak."
You can try to run the HK M-Series Heat Range 9 Plugs, 50003-M45HL. However, I don't believe this will cure the issue altogether. Might help but again this is my best guess as well.
Check each coil pack for the proper ohm value. I don't know what the ohm values are for the 2.0T Theta II engine right off hand. I don't have a shop manual but you can call your Service Department, AutoZone, NAPA or O'Reilly's, they should be able to tell you. I can tell you how to check them, once you have the proper Ohm values. If there's a bad one, it will get replaced.
This issue is; another reason to take it to the Service Department and let them do a diagnostics on the GDS. Typical codes the ECU will throw for such issues are ; Engine code - P0303, P03A5, P039B, P03AF, P03B9 and P0302. Which range from; bad coil pack/s, clogged injector/s, bad injector/s, bad spark plug/s.
Yep you're going to have to pull the JB4 as well. Also replace the spark plugs, with the original OEM units as well!
Cheap Possible Fix # 1; Buy 3
large black bottles of
Chevron Techron. Use one at each fill up, for the next three fill ups. Go to a top tier station to fill up also and not your local cheaper one.
Special Note;
It's possible it just might be a faulty
knock sensor but I'm not ready to go this direction. At least until we've ruled out others first. You don't have any plugs electrodes melted or electrode tip, ceramic insulators, cracked, right?
It's a process for sure but worth it in the long run. The more you learn now, the less you'll have to pursue in the future.
You might also purchase a
ODB Link;
https://www.amazon.ca/OBDLink-Bluet...DB+Lonk&qid=1564430318&s=gateway&sr=8-1-spell
So, you can check what's going on with the car as well. Invaluable little tool, will reads error codes and more. It will also allow you to diagnose and clear them also.
Long post I realize, sorry. However and unfortunately, there's certain more!. It's simply a process of elimination.