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So a few days ago my car developed a horrible misfire in cylinder 4 so I pulled the plug and the electrode was smashed to where there was no gap. Looked like something had hit it a few times. Replaced the plug, ran fine. Later that day boom another miss, cylinder 2 and 5. Same issue. So I replaced all the plugs. Now today was running great. Hitting boost no problem. No issues then boom, literally cruising at 3k and boom 2 more random misfires. And I bet the plug gaps are closed again. Any idea of what’s going on?
 

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What plugs are you using
 

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Not the right plug for the motor. May be melting them.

Get genuine volvo 8692071 plugs
 

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2005 V70, 2016 V60
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Are those longer than OEM plugs? Have you tried getting a borescope to look inside the cylinders? I would be looking for marks on the top of the pistons from hitting the plugs or a piece of something in there rattling around. That plug looks like it has been beat on.
Is there a reason not to use the Volvo plugs?
 

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Not the right plug for the motor. May be melting them.

Get genuine volvo 8692071 plugs
I got 19mm on the denso that he it using, do you know the reach on the stockers? It looks like they are 19mm as well?
Maybe slipped a tooth on the timing belt and sent the valves into the plugs?
 

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I got 19mm on the denso that he it using, do you know the reach on the stockers? It looks like they are 19mm as well?
Maybe slipped a tooth on the timing belt and sent the valves into the plugs?
I would take an OEM spec plug and measure it, then measure the plug the OP is using (and bending). Could be production differences regardless of the manufacturers published specs.
 

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I would take an OEM spec plug and measure it, then measure the plug the OP is using (and bending). Could be production differences regardless of the manufacturers published specs.
The fact that he ran the plugs for quite awhile without issue, and then “all of a sudden” had the issue would point to something other than plugs. What’s the timing belt/belt tension etc look like?
 

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I don't think the valves can hit the plugs, the plugs are always there never moving. The pistons - sure, but not the plugs.
The plug shown is missing part of the insulator and the ground electrode looks beat on with a tiny hammer around the size of the missing piece of porcelain. If I had to take a guess with the info presented, these plugs for some reason are losing bits that then beat the electrodes. Reasons might be that they are crap and Volvo OEM would fix this or the car is running too much boost and/or advance and knocking bad enough to wreck the plugs. The latter would likely be noticed.

I had a related issue with my Mazda 3. I somehow got a bad or counterfeit batch of NGKs and they would lose the tips, which then made an awful racket besides for misfiring. I had to crank the engine with the plugs out to blow the bits out the spark plug hole if I didn't want the next set to get banged up.
 

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The fact that he ran the plugs for quite awhile without issue, and then “all of a sudden” had the issue would point to something other than plugs. What’s the timing belt/belt tension etc look like?
I don't know enough about when the plugs were installed, how the OP drives, et cetera. I'd first check the specs on the plugs. That AC Delco plug is literally a $2 part, there are plenty of issues when non-OEM spec plugs are swapped for price, heat range, availability, et cetera. Yes I agree it sounds like an event happened, however I would still ensure the proper plugs are installed before I started removing a head.
 

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The fact that he ran the plugs for quite awhile without issue, and then “all of a sudden” had the issue would point to something other than plugs. What’s the timing belt/belt tension etc look like?
And also, there is no mention in the OP's first post that he 'ran the plugs for quite a while'. That is part of why I suggested what I suggested. You are speculating that anything happened 'all of a sudden'.
 

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And also, there is no mention in the OP's first post that he 'ran the plugs for quite a while'. That is part of why I suggested what I suggested. You are speculating that anything happened 'all of a sudden'.
Slow down and actually read the original post. He hasn’t had this issue from the day he bought the car, which means that the plugs have been ran in the car for awhile. He said “developed” an issue. And a “boom”, and a ”boom”. Booms don’t happen over time. They happen all of sudden. Just because someone doesn’t spell it out for you, doesn’t mean that certain things can’t be inferred from what was said. This BS that you are spinning is called semantics. Try to ”help” solve the problem, not create extraneous ones. There are several possible causes for the damage. The fact that the problem happened with plugs that where ran for awhile without issue, and then all of a sudden developed a misfire, would point to another issue than just the reach of the plug into the cylinder. If he slipped a bearing and the piston top hit the plug it would be a lot worse. I absolutely hope that it is something as simple as a plug, but the fact that it happened after, and only after the plugs were ran for a while......
 

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The piston isn't going to hit the plugs. It can't.

My money is on what island_V70 posted. Cheap, crappy plugs came apart, rattled around in the cylinder and caused the obvious marks on the plugs.
Could have popped....just strange that its happed again in such a short time on multiple cylinders, no?
 

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Could have popped....just strange that its happed again in such a short time on multiple cylinders, no?
Not sure what you mean by "popped".

The plug sits at the top of the combustion chamber. The piston cannot physically fit in there.

Something is rattling around, causing all those marks on the plug. My money is on the porcelain, which is clearly partially missing.
 

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I don't think the valves can hit the plugs, the plugs are always there never moving. The pistons - sure, but not the plugs.
The plug shown is missing part of the insulator and the ground electrode looks beat on with a tiny hammer around the size of the missing piece of porcelain. If I had to take a guess with the info presented, these plugs for some reason are losing bits that then beat the electrodes. Reasons might be that they are crap and Volvo OEM would fix this or the car is running too much boost and/or advance and knocking bad enough to wreck the plugs. The latter would likely be noticed.

I had a related issue with my Mazda 3. I somehow got a bad or counterfeit batch of NGKs and they would lose the tips, which then made an awful racket besides for misfiring. I had to crank the engine with the plugs out to blow the bits out the spark plug hole if I didn't want the next set to get banged up.
Did you actually make note of the NGKs that might have been counterfeit? Remember where you got them? Thats why I order straight through NGK. That sucks.
 

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Not sure what you mean by "popped".

The plug sits at the top of the combustion chamber. The piston cannot physically fit in there.

Something is rattling around, causing all those marks on the plug. My money is on the porcelain, which is clearly partially missing.
Yeah, the porcelain, the piece popped off. lol
 

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Slow down and actually read the original post. He hasn’t had this issue from the day he bought the car, which means that the plugs have been ran in the car for awhile. He said “developed” an issue. And a “boom”, and a ”boom”. Booms don’t happen over time. They happen all of sudden. Just because someone doesn’t spell it out for you, doesn’t mean that certain things can’t be inferred from what was said. This BS that you are spinning is called semantics. Try to ”help” solve the problem, not create extraneous ones. There are several possible causes for the damage. The fact that the problem happened with plugs that where ran for awhile without issue, and then all of a sudden developed a misfire, would point to another issue than just the reach of the plug into the cylinder. If he slipped a bearing and the piston top hit the plug it would be a lot worse. I absolutely hope that it is something as simple as a plug, but the fact that it happened after, and only after the plugs were ran for a while......
I did read the original post. The OP says both developed and boom, by your statement these are two different conditions. One is slow over time, and the other is immediate. Again, you are completely speculating by saying the OP has had the plugs in the car for a while - you don't know that. He says he changed the plugs after the first failure, then the failure happened again on different cylinders (and changed plugs again and is assuming the same failure yet again). Are all the plugs swapped in and out the exact same? Are they spec'ed for the engine? IDK. Given the lack of information I am going with wrong plug for engine, cheap plugs, or defective plugs as an initial diagnosis because I don't know more. Maybe its something else, maybe its what you suggested. IDK. But instead of debating the minutiae perhaps you might want to be open to suggestions other than your own. Just a thought.
 

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I did read the original post. The OP says both developed and boom, by your statement these are two different conditions. One is slow over time, and the other is immediate. Again, you are completely speculating by saying the OP has had the plugs in the car for a while - you don't know that. He says he changed the plugs after the first failure, then the failure happened again on different cylinders (and changed plugs again and is assuming the same failure yet again). Are all the plugs swapped in and out the exact same? Are they spec'ed for the engine? IDK. Given the lack of information I am going with wrong plug for engine, cheap plugs, or defective plugs as an initial diagnosis because I don't know more. Maybe its something else, maybe its what you suggested. IDK. But instead of debating the minutiae perhaps you might want to be open to suggestions other than your own. Just a thought.
Good luck. Hope he gets it sorted on the cheap. The experts have spoken. I’m out... Cheers.


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