one plug wears only on the center electrode and the other wears on the side electrode, the direction of current flow is different on them... The multi coil gm cars have plugs wires on all of them and they still do this. Actually these plugs were changed just about when they specified with these long life intervals on them , no emissions problems , she just wanted the routine mileage maintenance done. In fact she didn't know that the plugs were required at this time, along with a bunch of other stuff.





Quote Originally Posted by gale
Makes sense to me, the one closest to the coil is going to have a higher voltage delivered to it vs. the higher inductance and resistance losses on the one fed by the wire & the closer one will ablate away more metal at a faster rate. I'm surprised the Mercedes engineers designed them like this and didn't mount the coil mid-way between the plugs and feed them both with equal length wires. Looks like the plugs had a few too many miles on them and probably had some idle/emissions issues?