100 Series 4.7 V8 Spark Plug Doesn’t Fit (1 Viewer)

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G-Cat

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This post is strictly to document an issue that someone may search for in the future, as my Google IH8MUD search did not provide what I needed. The issue was one of the 8 spark plugs being bigger in circumference than the other 7. We tried, and failed, to get an OEM-spec spark plug into cylinder #6 for a good 20 minutes before we realized.

For search purposes: can’t get spark plug back into
engine

My 1999 100 Series Toyota Land Cruiser USDM with 4.7 liter 2UZ-FE V8 and 290K miles has been demonstrating a “miss” or a stumble at idle. It is worse with transmission in drive than in park.

No Check Engine Light (CEL) but past experience tells me it is either one of the 8 Direct Ignition Coils (often referred to as “Coil Packs”, Toyota Part Number: 9008019027), one of the 8 spark plugs (Toyota Part Number 90080-91180) or a combination.

If you have access to a code reader that reads “real-time”, rather than one that only reads if a CEL has been tripped, best to use that to try to identify the exact issue. I don’t have that access, so...

Low on cash and needing it fixed right now, I purchased 8 off-brand Coil Packs and 8 Denso Spark Plugs for the price of 1 OEM Toyota Coil Pack from Amazon. I don’t recommend this...always go OEM, but it was this or nothing.

Everything went smooth, until we got to cylinder #6. It was a little harder to break loose. Once out, we noted that it looked weird, but it was hot out and we’d had no issues so we kept going.

The new Denso, that had easily installed in the other 7 cylinders, would not thread in #6. We had misplaced the plug we took out, or we might have figured it out sooner. Once we retrieved it, and held it side-by-side with a new Denso, the problem was obvious...the #6 plug had a bigger circumference than the rest:

6827E0CE-57C0-4B0C-B492-F5C2E8B589E9.jpeg


Top view

0B90A2BB-479D-439F-A9FF-76ADFE21F907.jpeg


So, it turns out about 6 years ago I had an engine issue that left me on the side of the road. I had just had all 8 plugs and packs replaced by a local shop. I had it towed and was told that a spark plug had broken and they replaced it and I was good to go.

Obviously, there was more to the story. I don’t know if they had cross-threaded a spark plug when It was in for the new coil packs/plugs, but the cylinder threads in #6 were boogered enough that they had (likely) enlarged the threads with a tap and then installed an OEM plug with one of these:

94B08242-FD87-475E-9B90-D6A2140EA184.jpeg


I got this one at O’Rielly’s. We installed it on a new Denso, with a little Locktite, and then it installed in #6 perfectly.

Long post. Likely obvious to most...but I’m still a 1-2 banana mechanic so I’d thought I’d share.
 
BTW, the new plugs/coils seems to have fixed the issue.
 
With those "teeth" at the top, are you sure it is threaded completely and down enough in the cylinder head? If so, how did you know?
 
I don’t know, but this item is made for this application...and the plug we removed had 50K miles on it and, once all 8 were replaced, it’s running great.

Other searches led to folks with issues getting spark plugs to thread being quoted $3000 from Toyota dealers to remove the head and fix.

I’m no expert, simply relaying what I found!
 
Have the same problem but with #5

0EAFD40D-F244-49C9-816C-92D4BB7B58A8.jpeg
 

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