Originally Posted By: 01rangerxl
Since we're on the topic, when should OEM "100K mile" plugs be changed ideally? Are they really good for 100K? My 2001 Ranger had the original plugs at least until 93K miles and it still ran great, even after a Sea Foam treatment. My current one has the original plus too, but only 71K miles.
My belief is that go to about 3/4 of what the manufacturer says, so I'd probably put some new ones in about now. Unless you've got the funky plugs that Ford put in the 5.4 engines. They usually break, so get them out much sooner.
Back when I was turning wrenches, I saw a Windstar come in with a CEL on. The plugs had 254K miles on the original factory plugs. Funny thing, the CEL came on because of a vacuum leak, not because of bad plugs. We replaced them anyway. They had a gap about like what the original photos show on this thread.