97 Expedition Fouling out Plugs

I had the tuneup done at 80k because that's what my mechanic said I need. Ok no problem till my check engine light came on again took it back to the shop
he said that the no. 4 plug had fouled out. He replaced it and about a week later it rained, my check engine light came on again. Took it to the shop no. 4 plug fouled out again. It took me about three times of it raining and my plug fouling out that I noticed a patteren. I asked the mechanic if there was somthing that they had done, to cause this and he said no. To cut it short, has anybody had the same problem with no. 4 plug fouling out when it rains? I did not have this problem before I took it in for a tuneup. Help
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Ok
shop
week
and
there
it
the plug wire to number four is probably damaged......Its got 80K on it? It wouldnt hurt it to have new plug wires.
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Yes, you need new plug wires. I have had to had my back 2 wires replaced twice now.
Lynn
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