I have an 09 R56, N14 with 98k. I've been working on the car due to misfires in 1, 3, and 4. During my initial inspection, I boroscoped the cylinders and discovered very little carbon build-up on top of the pistons. Compression showed about 165 to 175 in all cylinders. A leak-down test indicated air escaping through the intake valves. The intake valves had plenty of carbon buildup so I walnut blasted them clean, but I'm still concerned about the lack of carbon buildup in the cylinders/pistons. You would expect to have carbon build up after 98k miles.?

I've viewed several sites that say I may have wash down inside the cylinders that is being caused by leaking fuel injectors, but all the cylinders were similar. Do you think all the injectors would start to leak at the same time? Up until the misfires, the car seemed to run well. Don't want to end with hydrolock. Any help is appreciated.

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