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- In my extremely limited knowledge of spark plug reading, these look totally normal. They all had a small 3-4mm spot of carbon in random places around the rim near the insulator. Appears to be normal when compared to other N55 plugs I’ve compared them to.
- Prior to swapping out the plugs I ran some diagnostics in ISTA+ (BMW’s application that techs use) and paid extra attention to the “rough running cylinder values” as described in the tech notes. Anything within +/- 7.00 on the display was acceptable and prior to changing my plugs those value were all within +/- 2.00
- After swapping those values appear to be close to +/- 0.5 !!!