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Originally Posted by irieite
Thanks for the info. I currently have the Bosch H8DC0 plugs in it, (about 10k miles on them) but I've heard some really good things about these Beru Ultra-X plugs. They have four ground electrodes, like the Bosch Platinum +4, but have a larger copper based core, so they fire better in earlier CIS injected cars.
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This is marketing BS. Muliple ground electrodes are not necessary, and, in fact, can cause poor performance on many engines. The archives are full of complaints about these plugs. All those metal electodes are "cold" relative to the flame kernel that the spark starts, and all that cold metal can quench an incipient flame causing missfire.
Also, of the four listed plugs, only the Bosch H8DC is a proper NON-RESISTOR plug for a Mercedes engine.
Stick with the H8DC0 (heavy duty electode) or the less expensive H8DC (standard electrode), which work just fine.
Most spark plug problems (idle roughness or emission test problems are common) are caused by using non-OE type plugs with resistors, mulitple electrodes, whatever. The best advice is to install OE equivalent plugs, and when accomplished "spark plug problems" usually go away.
Duke