I rebuilt this motor on this car and when I first start it it runs rough and miss fires a little, but then it runs fairly smooth, I have noticed that when I pulled the new plugs, they were very black and sooty after only running for about 10 miles, meaning it is running rich ? what would cause this ? it is a 2009 Clubman S, I have changed the coils and the MAF and the valve cover , some help would be appreciated

 

I upgraded my MCS to stage 2 parameters (ECU tune plus intake and exhaust hardware upgrades). After walnut blasting, I experience misfires with the stage 2 setup. I fixed ALL of the intake manifold leaks at the clamps -- there were 2 culprits: one where the clamp on the cold side of the new intercooler was not placed on "squarely;" the other was an incorrectly seated intake hose on the intake manifold. I considered my spark plugs (DENSO # 3461 IRIDIUM) and coils (Delphi GN10571) to be relatively new (installed 2021), so I used them with the new stage 2 setup only to continue experiencing misfires. After all this, my misfire was finally cured by installing new plugs (NGK Laser Iridium Spark Plugs (NGK 97968)) and coils (Bosch 0221504470) recommended by M7. I know the stage 2 configuration requires the stronger spark delivered by the new ignition hardware, but knowing this, I would have installed them in my OEM engine, as well.


Check intake hoses and try upgrading your coils/plugs.