Just wanted to add:

*stock coils are highly recommended and can support much more HP than motor is ever capable of
*good plugs like NGK laser IR will be a good choice unless you are going to push boost >25lbs.. you may want to get a plug you can gap for boost that high, or worry about blowing out your spark


Ive found similar issue with my JCW was largely corrected by an oil change.. which leads me to believe there is likely some PCV issues with the turbo inlet affecting boost pressure and causing ECU to pull spark timing.. Im going to be installing my catch cans once they arrive, and plan on venting the turbo PCV to atmosphere. Ive followed good results with other folks that have done the same and claimed it effectively removed near all of this 'stumble/fall on face' behavior when accelerating.

 

Just to update my issue with the stumbling/power drop-out....did it for 2 or 3 weeks, now cannot duplicate. Several tanks of gas from the same station I always use, Union 76, and always 91 octane, the best we can get here in SoCal. I also do not fill up if I see the tanker putting gas into the underground tanks. Could it have happened a few minutes previously? Sure. Maybe I got some bad gas on several fill-ups? No idea. I just hope that was the issue, as my aftermarket warranty is about to expire in less than 1k miles. New in-tank fuel filter will be installed as soon as I have time to do so. As to the scan tool that I use, it is a small hand-held Matco unit that has always shown codes on many vehicles. I do not recall the model number, but it did show me many codes when my HPFP was failing. That was with the CEL illuminated, so no idea if it can read codes that may not trigger the light.

I also wanted to mention that I DO adjust the gap on the NGK Iridiums, due to my JB+ adding boost. I close them down to .024 inches. There are many ways of doing this, what I do is use my spark plug gapping tool to "gently" tap the ground electrode to the desired spec.

 

I finally had a chance to work on the Mini last weekend. I purchased NGK blah blah blah plugs and new coils also. The necked down portion of the electrode was worn completely away on one plug and down to a tiny stump on the other three plugs, so I tried first with the new plugs only before installing coils.

The plugs alone eliminated the misfire.

 

Glad that the plugs fixed your issue, Longitudinal! Should they wear that quickly? Probably not. But, they do. Cheap fixes, love them! I do my plugs every 20k, just to eliminate those from the diagnostic chart if a problem should arise. My 2011 is still running fine, so I am going with "bad gas" for my issue, however unlikely that may be. Nope, have not changed the in-tank fuel filter yet, and now I am about 700 miles from my warranty expiring. Fingers crossed....LOL!

What kind of plugs did you remove? Were they Brisk? I think Brisk was the OE supplier. The NGK Iridiums seem to show less wear over miles versus the Brisks, at least in my experience. I still do plugs every 20k. Those Brisks scared me into it! LOL.

 

Time to delete your second general rule of engine diagnostics, eh? Glad you got it fixed and it was simple.

 

I will edit my second rule of diagnostics: "In my 25 years of working on cars, it was never the spark plugs until I bought a Mini."

 

I guess you never owned a Subaru. Had to change the plugs every 30K in that POS car or it barely ran. It drank oil too. At least changing plugs in the MINI is easy, in the Subaru it required creative use of extensions and flex joints.

I changed my plugs at about 50K, maybe they could have lasted a bit longer but the car ran noticeably smoother with the new plugs.