Triton eating #4 spark plug

[Brandon K]

So last December I finally got around to finding the source of a random misfire that would come up maybe 6 times a year. The Expy idled fine, had plenty of power, and generally behaved normally. But that darn misfire, only under load at highway speeds, was nagging. Finally I decided to pull all the plugs to just see. The previous owner had said they were all swapped, at unknown mileage, so i figured worst case was I would find out immediately if that was true. Sure enough they all came out smooth as butter and this BEAUTY was waiting for me in cylinder number 4. Just look at it:


Remember this was running JUST FINE 99% of the time. All the plugs were E3 diamond fire's, all looking worn out, but none so spectacular as like cyl 4.

So I changed all the plugs with an Autolite replacement. This was December 12th. Now about 8 months later it starts to misfire again. The scanner says cly 4 but the power balance test isn't so conclusive. The very enjoyable task of pulling #4 yielded this:




Soooooo, does anyone have any idea why the engine would be destroying this specific plug? Is it just a fluke and my catalytic converter was craving some spare metal chips? Is my stock coil just too powerful for the cheapo autolite plug?

Note the engine has no noticeable coolant leak, all injectors were refreshed last year also, and no codes are being thrown for anything. 116,*** miles, 2006 Limited 4x4. Tonight I also changed the coil on #4 to a spare I had just incase.

 

[99WhiteC5Coupe]

I don’t have an answer - but I would suggest using the correct OEM Motorcraft spark plugs (and Motrorcraft coils if replaced).

 

[SafariGoneWrong]

I installed the Autolite HT series spark plugs back in 2013 after 6 of 8 original plugs broke coming out. At the time, I refused Motorcraft as a replacement. The Autolites came out about 4 months ago after 40K miles, came out without issue and looked great. We know getting to #4 is a PITA but I wonder if getting a suitable borescope down the spark plug well may tell us anything. The blueish color of the plug that sits in the well is something I haven't seen in my 2 spark plug changes, and the rusty color of the first E3 plug seems very odd. I'd pressurize the cooling system and see if there's any getting into #4...easier said than done I know.

 

[whtbronco]

The only time I have seen anything like that was on a Honda. Once we gave in and put the factory $12 Honda plugs in it, $12 each in 1992, it was fine. Every other plug it burned everything off the end within a couple hundred miles. Just 1 plug, The coil maybe. The borescope and coolant pressure test suggested by @SafariGoneWrong are good ideas.

I too have become a fan of the factory plugs in most modern engines.

This $20 ratchet makes plugs 3 and 4 easy to swap. It's worth it if only for those plugs. I have also used it for temp sensors on GM 3800 V6 engines. It's not a great ratchet, but for these tough to reach places it's the greatest thing ever.

3/8 in. Drive T-Bar With Flexible Ratchet

Amazing deals on this 3/8In Dr T-Bar With Flexible Ratchet at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

 

[SafariGoneWrong]

This popped up in my YouTube suggestions this morning...didn't even search for it! Around the 13 minute mark FTM/Brian and his son go over a strapless plug. It starts off with diagnosing the usual ticking sounds. https://www.youtube.com/watch?v=uyexvVeBws4

 

[Al Steel]

Most likely solution is also the simplest, under torqued, non-OEM plug. Pick up a MC plug from a reputable auto shop or dealership. Amazon, et al, are notorious for selling Chinese knock-offs as OEM.

Makes sense, #4 is a biyatch to get to torque down properly. I'd get a MC plug and make sure it's torqued down to spec. You can't go by "feel" on these. Get or rent a proper click or digital torque wrench.

If you aren't inexplicably losing coolant over time then coolant in the cylinder is doubtful. You could do a leak down test as others suggest but I'd start small and work up to bigger issues.

G/L !