85_Ranger4x4
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I went through the whole tune up procedure a little while ago. Plenty of busted knuckles on the plugs. I went with Iridium plugs, E3s I think. The ones with the four point spark instead of one. Didn't notice much of a power increase but gas mileage went up 1 or 2 mpg and it idles a whole lot smoother than before. Plugs weren't really fouled or anything but I didn't know the last time they had been changed so I went with high quality the first time around and so far they work great.
Not to scare you or anything, but my brother changed a set of those out of a V-10 and a couple were missing several electrodes altogether...
None of those 4 are exactly the same distance from center electrode, so it is going to spark from the closest one.
I bet your milage gains are from replacing worn out plugs with new plugs... not because they have four electrodes.