1NZ-FE Spark Plug Ejection/Coil Pack Melting (2009 Yaris)

[Guyon]

This is a new one for me! Car was acting totally normal and then threw a suddenblinking CEL. Got off the highway safely and heard it misfiring. Got a tow to Advance and ran the code to find only P0302 (cylinder 2 misfire). Pulled the coil pack and the spark plug came out with it. Wow, it was hot in there! Threads on the head are gone. Might try to throw a Heli-Coil Save-A-Plug at it.

At any rate, has anyone seen this happen on a 1NZ? What would have actually caused this?

[mitch9521]

That ain't normal, holy shit lol

[Guyon]

Follow-up: my theory is that I didn't tighten the spark plugs enough when I put these plugs in. I'm always careful not to over-torque them, but judging by half the threading being fine, it looks like the plug backed itself out some over the 30K miles they've been in there.

There's a few local cylinder heads out there for ~$200. May toss one of those on instead of Heli-Coil/Time-Serting new threading.

[remcafee]

yeah sure looks like a spark plug got loosened, not 1nz specific but any engine specific, ran into this a few times over the years of working on cars where plugs are loose and the plug well threads blow out with it.

[Guyon]

Follow-up: the spark plug threading on cylinder #2 was shot. I ended up fixing this with the Time-Sert 4412E-111 kit. Yeah, it was pretty pricey, but I do want this to be a permanent fix.

It was pretty straightforward to do even without removing the head or even the valve cover. To make sure I was on a compression stroke (to ensure the valves were shut in the cylinder), I had my wife hold a plastic bag over the spark plug hole while I rotated the crank. When the bag sucked in, I knew I was on an intake stroke. When the bag blew out, I knew I was on a compression stroke. When it blew out, I stopped and placed a long screwdriver down the hole onto the face of the piston and continued rotating a little bit to ensure the piston was still going up. I stopped far from the top so that I wouldn't accidentally hit it with the tap.

One thing nobody can stress enough: coat the tap with wheel bearing grease when tapping the threads. This video is all the reasoning you'll need. The 1NZ-FE spark plugs have 12 threads. I chose to do six passes with each pass being two full rotations. Coat the tap with grease (as he does in the video), cut two threads, pull it out, clean the tap, rinse & repeat.

When performing this job with the head on you also need to be conscious of how deep the insert is being placed. This is a little less of a concern with the Time-Sert kit than the Heli-coil kit, but still something I didn't want to mess up (lest the spark plug isn't deep enough or worse, too deep). We figured out a trick for this too - when tapping, there's a point where turning the tap gets really easy - this implies you're all the way through and into the cylinder. When this happened, I stopped immediately and took a blade and cut a notch on the wrench that turns the tap (at the height of the top of the spark plug hole). This ensured that I could take the tap out and put it back in and still know where the "bottom" was.

I cleaned the tap, and before placing it back in I cut another notch ~6mm above the first one on the wrench. This time when I placed the tap in, I rotated the tap until the second notch was level with the top of the spark plug hole. This is the way to accomplish step 6 in the instructions without having the head off.

Once the seat was cut, we took a few measures to try to eliminate the metal shavings that still made it in there (despite the bearing grease, it's inevitable). First, I vacuumed what I could. Second, I took a long thin rag, draped it over a screwdriver, and pressed it down through the spark plug hole into the cylinder and rotated it some and pulled it out. I did this until no more metal shavings came out. Next, I took a piece of stiff vacuum hose and pressed it against the seat that was cut repeatedly until I got no more metal shavings from that (which surprisingly got plenty of metal). Finally, I blew air into the cylinder to try to force some out that way (remember - it's on the compression stroke, so the valves are shut).

Installing the insert was very simple. I replaced all four spark plugs, replaced the coil that had cooked itself, and the car started right up! The nugget lives on! Can't kill a Toyota!

[komichal]

I would never trust myself that I can do this without removing the head.