Spark Plug Diagnosis? (Removed After Misfire)

jaymar

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Had a consistent P0301 (misfire on cylinder 1), whole truck would shake a bit after idling (or running for a short time if I turned the key and moved immediately). Replaced the plug and no code thrown. Everything after the coil replaced with new OEM about 3 years back. Plug tube seals as well. Wondering if someone with more experience than I have can take a gander at the old plug and suggest a cause. The gap looks bigger to me on the old plug, like the electrode/s have been partially vaporized. (I'm assuming the side electrode didn't bend. :) )

History: Engine runs a pretty constant P0130 or P0133 and/or P0170--but if that was a major contributor, wouldn't I have misfires all around? Reason I changed everything out 3 years back was, some time after purchase, had a major misfire on #6, felt like the whole truck was going to rattle apart. I actually had it towed the half-mile home; it was that bad. #6 plug was covered with oil. No ignition issues since--until now.

Two shots of same old plug--then again beside the new. Thanks for any help!











No 1 Spark Plug A (removed 10-19-2021).jpg

No 1 Spark Plug B (removed 10-19-2021).jpg

No 1 Spark Plug C (swapped 10-09-2021).jpg
 
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The electrode does look a little burned down but not enough to cause a misfire. I just changed out all of my plugs last week and the electrodes were much worse, like almost completely gone. They actually still ran fine. Just thought I'd check them because I hadn't looked at them since I bought the truck almost a year ago. Have you looked at the injector as a possibility?
 

jaymar

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The electrode does look a little burned down but not enough to cause a misfire. I just changed out all of my plugs last week and the electrodes were much worse, like almost completely gone. They actually still ran fine. Just thought I'd check them because I hadn't looked at them since I bought the truck almost a year ago. Have you looked at the injector as a possibility?
Not yet; figured I'd try the simplest/cheapest fix first. Could be I'm just addressing the symptom though. Thanks for the tip!
 
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I think its not terrible, but not great.

I agree it looks a bit sooty / carbonised.

Also think it could be a bit of oil being burnt. Are you losing oil? Or seeing any blue smoke in the exhaust.

How many miles on your engine?

Mine was burning oil, and ready for valve stern seals at 200k km (130ish miles)

If it's burning oil, the sooty residue on the plug might have an oily consistency if you rub it
 
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@Rusty Marlin - so why then is #6 associated with HG failure and #6 plug is the worst of the bunch?

Several reasons. #1 & #6 are more likely to be failure points on HG.
Its at least partly due to thermal expansion of alloy head at a greater rate than cast iron block.
The cumulative expansion of alloy in the head is greatest at the two ends. So the head grows longer, then returns to normal length on every heat cycle. This frets at the gasket, mostly around #1 & #6 pots as the ends of the head moves more than the centre.
 
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20211021_231734.jpg


The black stuff on the ceramic portion at the top of the plug (red arrow for clarification). Sometimes a bad plug will find less resistance to ground on the outside of the plug, straight to the cylinder head, vs the normal path inside the cylinder and across the gap. Usually a carbon track (looks like a black line where arcing has occurred) will also be evident inside the plug wire boot if this is occurring.
 
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You talking about the stain on the top part? (Upside down).

I was wondering about that too. What's that? Leaking compression through the body of the plug?
Not sure why the plug will turn color like that other than just possible heat exposure? All Toyota Denso plugs I have replaced do it in varying degrees at normal (i.e. not malfunctioning or premature failure) intervals. (Camry's, Corollas, Priuses, Tundras, etc...)
 
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View attachment 2818293

The black stuff on the ceramic portion at the top of the plug (red arrow for clarification). Sometimes a bad plug will find less resistance to ground on the outside of the plug, straight to the cylinder head, vs the normal path inside the cylinder and across the gap. Usually a carbon track (looks like a black line where arcing has occurred) will also be evident inside the plug wire boot if this is occurring.

Nice explanation, thanks 👍:beer:
 

LINUS

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@Rusty Marlin - so why then is #6 associated with HG failure and #6 plug is the worst of the bunch?

The HG was redesigned / update for the cooling jacket oriface - I forget if they went bigger or smaller but the ‘95-‘97 is where that‘s the problem HG.

The thermal expansion is the root cause & why you see #6 cyl to cooling jacket as the common failpoint.

That’s why if you do pop a HG, you want the update design so you don’t have to think HG problems again, at least not from gasket design fault.
 

jaymar

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The electrode does look a little burned down but not enough to cause a misfire. I just changed out all of my plugs last week and the electrodes were much worse, like almost completely gone. They actually still ran fine. Just thought I'd check them because I hadn't looked at them since I bought the truck almost a year ago. Have you looked at the injector as a possibility?
Hmm you're right; the misfire is back after new plug. Not constant, but it's there.
 

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