I just replaced my spark plugs while changing resistor tips anyway. The car is my '89 190E 2.6. I used NGK copper-core plugs gapped at 0.032". The old ones were Bosch DCO Super plugs that my technician had purposefully gapped at 0.045".

What was he tweaking by putting them so far out of spec.? I ask because I may wish to do the same, as the car now runs smoother, but with less power.

Thank you for another tap into the knowledge base, Andrew Seidel.

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89 190E 2.6
83 300TD Turbo
75 240D

Resistor ends, if you had bad ones, would account for the smoother idle. The 0.045" plug gap is a bit wider than usual(I like 0.040"), but real close. I think we've discussed the theory here before,but the point is that the wider gap uses a bit more of the stored potential current from the coil. It makes a larger/hotter spark. That is a good thing. The down-side is that the later style small coils don't have a lot of reserve, so I wouldn't go wider than 0.040".
If you're going to use NGK plugs, put a bit of anti-sieze on the threads. They don't have the nickel plating like the Bosch DCOs.
Regards,
Randy D.

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