I was going to say the same thing without even listening... sure enough that's exactly what it sounds like. That a plug has ejected itself.
There are a number of kits on the market specifically for the 4.6 to restore the thread with the head on the car. I used the helicoil one on a '99 GT. No drilling required with that kit (the tap is designed to remove the minimum amount of material). Just went slow and easy with lubricant on the tap, taking it out frequently to clean off chips so they didn't fall inside the cylinder. Once tapped a vacuum cleaner with a small hose attached to it (homemade attachment) did a good job of sucking out the few chips that did fall in. Turning over the engine with the coils upluged was another step to eject anything that may have been left out the open spark plug hole.
The downside is that the kit is $200. But the tool and the tap is specially designed to get down the deep spark plug wells.
Those with superchargers and such might want to consider one of the kits with more robust inserts. But those require drilling the hole larger, which means more chips, etc and so on.
It takes awhile for the code to show up. On that '99 it didn't show up right away. When a coolant was shorting one of the plugs on my '97 it took miles of driving and purposely accelerating hard enough to make it happen before the MIL came on.
I've Googled this issue and some say that rethreading is only temporary. Called the local Ford dealer and he also said that usually they replace the head (a couple of grand he told me).
Is replacing the head something I can do in the garage? How much will it cost for 2K GT? I don't want to junk it just yet since I just had a new clutch kit put in and new tires as well :-(
You guys were right. The plug closest to the passenger is out. The coil boot is shredded but the coil itself looks ok. How can I tell if the threads are damaged or is it a given? (It's hard to see into that far hole.) Should I just try to install a new plug and see if it's tight. I did find a local guy that said he'll put a new helicoil for around $200 plus I'll need about $100 for tow.
peer down in there with a flashlight to see how damaged the threads are. It's a given that they are damaged, otherwise the plug wouldn't have come out. There might be enough left to get some threads to bite but a plug won't stay there for long. At best enough to get to the shop, at worst not enough to get out of your garage.
I forgot to mention, the helicoil kit for the 4.6L doesn't use the standard spring insert. It uses a steel insert with male and female threads on it. The female threads duplicate the ford's 'half thread' design original to 4.6L heads up until when they were changed for this problem. That way you don't have to worry about making sure to have a full thread plug in that one hole.
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