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Our '04 Navigator is due for plugs & boots (well I can't find any indication they were ever changed, and at 152k it's likely time regardless)..
I can't seem to find any specific write up on how to do this for the DOHC engine.. is there anything unusual? I'm guessing in typical V8 fashion they're a PITA to get to, at least at the rear?
Well in case anyone was wondering, this is a super PITA.
I spent longer on the driver side rear plug than I've ever spent on a full spark plug change in any other vehicle including the 16 plugs on my 2012 Chrysler 300c Hemi.
If you undertake this job make sure you have a large variety of extensions, u-joints, wobble extensions etc.
All in all took me 6 hours, but over 2 of that was on one spark plug trying to figure out the correct combination of extensions to get around the hard line that goes right above it..
3 front on driver side are a piece of cake after removing power steering reservoir.
All 4 on passenger side are a PITA due to snakes-nest of hoses sitting on valve cover.
But hey it's done, and I don't think it'd been done in the Navi's 152,000 miles so it was worth-while.
Then you'll be happy to know they were changed on schedule at 100K miles. I changed a set of originals at 140K and the gap was 3X as wide as it should've been. Not that you knew at the time, but you could've gone another 38K miles before changing them again.
Interesting, in all the service history I could find no record of spark plug change, (and it has full dealer service history past 120k miles)
I've also never seen a plug look that bad at 100k... I changed a friend's Honda Pilot at 165k and they looked about like these. I did my Cadillac (Northstar) and wife's Civic both at 100k back some years ago, and both looked much better than this (no charred black stuff etc).
Oh well, better to have done.
Only possible regret now is I put in NGK-R copper plugs so I'll be due again in 30k or so, and it's such a PITA..
On the other end of the spectrum, I changed my Focus ST at 30k (interval is 100k) and they were all well out of spec at the time, and new plugs made a very noticeable difference in engine smoothness.
