My R61 manual (70k miles) has developed a misfire that occurs only near redline (about 5-6500) rpm under full throttle (high load). The CEL lights on after the misfire

Work performed so far:

• Replaced spark plugs and ignition coils
  
• Ran two bottles of Red Line SL-1 fuel system cleaner through the injectors
  
• Performed walnut blasting
  
• Cleaned the throttle body
  
• Replaced the intake manifold
  
• Inspected cylinder walls and valves via borescope (no abnormal findings beyond typical wear)
  

There are no vacuum leaks per smoke testing. The misfire is isolated to high load at wide-open throttle and does not occur during partial throttle or normal driving conditions.

My mechanic wasnt sure what exactly the problem is and told me the misfire is kind of minor (the fuel ran a bit lean) which makes it hard to diagnose and if they want to check it the next thing they will do is to look into all the wires.

Does anyone have experiences on similar issues???

 

What model year is the car? If it running lean at high rpms, it could be a fuel supply issue starting....

 

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It is a 2014 model, it doesn't look like injectors are clogged from borescope. There is no error code whatsoever. It is perplexing why the fuel would run lean.......

 

Injectors could be fine. Your fuel filter could be clogged and not allowing enough fuel at high rpm loads. Low pressure fuel pump could be going out. And, while not as common on the later N18 engines, the high pressure fuel pump could be aging.

On my older Clubman with early N18 engine, the high pressure fuel pump would get heat soaked at time, and not provide enough fuel for the load requested. Engine would stumble, misfire, and see boost cut. If I didn't ride it long enough, not codes would be stored. Only if I stayed on it would the engine fault hard enough and store a low fuel pressure code. I'm not necessarily saying that's your problem, but you might have to think outside the box. Normally, I would say misfire = plugs and cols. But, nothing is normal with these cars.