98 Ranger 4.0

[mikejb]

I had my old mans Ranger over the weekend to change the plugs and put a new belt on. He has had the truck since new so this is the first time the plugs and belt had been changed. The truck has 78k on it and cylinders 4-5-6 plugs were pretty worn down with the gap in the .065 range. When swapping the plugs in the 1-2-3 cylinders the plugs still had the platnum tips on the plugs and were still in factory spec in the .055 range.

What would cause one side of the engine to melt the plugs like this and leave the other side normal? I asked my Dad what gas he is using and he said 87 octane. I know a few years ago he never put 87 in. Anyone have any ideas?

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[Zoom]

I'd guess it's the way the engine fires. One side fires from the center electrode to the ground electrode, and the other side fires just the opposite. That's why it had single platinum plugs in it too, if you look closely both are platinum but one has the platinum on the tip and the other on the ground electrode.