MB selects particular plugs for a reason. Stick with what was already installed.

I can't imagine how you could run an engine with different plugs with varying heat ranges...combined with the octane you are using, could make for some pretty interesting timing issues. At best, use a complete set of plugs of the same heat range.

But. I'd go back to the 2 W8DC. If you can't find them, check with the MB parts counter...bet you get a different answer.

I would imagine that you may have a problem with old plug wires too. Pulling them off and reinstalling after replacing the plugs could have disturbed their integrity...

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2001 CLK430 Cabriolet (80K) - Wife's car
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2016 Mustang (32K) - Daughter's car