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The 5.4 3valve engine has the spark plugs that break off in the head when trying to remove them, the plugs were redesigned in 2009, the problem was the end of the plug was smooth and extends into the spark plug hole, this would accumulate carbon, when trying to remove them, the carbon would cause the end of the plug to seize as it is turned causing it to break. The new plugs have threads all the way to the end, this will remove the carbon as it turns. I have heard that Champion makes a replacement plug for the 04-08 that has threads all the way to the tip of the plug. The older 5.4 2valve engine had the problem with plugs blowing out, the only thing I can tell you from experience was that these plugs would loosen up if not torqued correctly and the compression would blow them out and take the threads with it.