Hi everyone, I'm having a very odd issue with my 2012 Cooper S manual. After about 50 miles of driving (not continuously) I get misfire codes for either cyliners 1 and 4 or 2 and 3, usually it's 2 and 3. I changed the sparkpulgs and coils with oem plugs and Bosch coils to see if that would resolve the issue and nothing, cylinder pressure is perfect, and while the check engine light is on it doesn't go back into limp mode when I restart the car until the light turns off on it's own or I reset it. The odd part about the whole thing is if I put fuel injector cleaner in the tank I can go through a whole tank with no issues at all and it runs perfectly until I refuel. And yes I do put premium Everytime.

 

Define perfect cylinder pressure please.

The two thing's I'd do are 1. Put the car on a oscilloscope and see what the injectors are doing (you're looking for an intermittent signal. 2. Check the base engine timing.

Keep in mind that all of the grounds for fuel injectors and ignition coils and controlled by the engine computer.

 

HPFP needs looked at.

 

The pressure does fluctuate around +-700psi but the dealer refuses to even look at it for warranty until the check engine light is on.

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It's your HPFP. It's a known issue with the 2012s. They even extended the warranty on that part to 120k miles.