re: 2004 F150 4.6L

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you mean the small rubber plug with a clamp on it? i had a 04 f150, & changed that thing 3 times. i have a 2015 f150 now.

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The earlier 2V engines spat out plugs, more often the 5.4L and 6.8L ones. After 2001 the heads were updated for fully-threaded sparkplugs. The issue was mostly due to improper torque on the plugs. The early 3V engines had a two-piece sparkplug design that had the opposite issue, they became seized in the head.