05-12-2020, 06:59 PM | #1 |
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My car DESTROYED a spark plug
Just wondering if anyone here has ever experienced a super knock condition causing a spark plug to almost literally shatter and shut the gap?
2016 F31 26K miles Lots of 89 octane fill-ups by previous owner Super knock at about 4.5K rpm... with cylinder shut down immediately after (all cylinders, except 1) and totally repeatable every time
Is it even possible for an N20 piston to reach the spark plug without hitting the valves first? Could severe pre-ignition/detonation cause this kind of damage? My thought right now is a "leaky" injector... I have a full online diagnosis from my shop. If anyone helpful wants to see everything they have done, I can PM you the link. |
05-12-2020, 08:20 PM | #2 |
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By "totally repeatable every time" do you mean that you always get a big knock event at 4.5k RPM? And then when doing this one time, you got the damage shown here? Just trying to understand the sequence of events.
Also, were these plugs every changed? Asking because a common mistake is not using a Ujoint or flex socket and cracking the ceramic during install and torque. Yes, knock can cause the gap to be pushed closed; it can even break off spark plug tips. Not sure about the damage to the ceramic though, that's why i asked the question above. |
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05-13-2020, 08:41 AM | #3 |
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Has anyone confirmed that those are the correct spark plugs? I'd go to the NGK website and look up the spark plugs for your car and compare the item numbers. If they do match, are they legit? Numerous threads on car forums about bogus Chinese knock-offs being sold on Amazon, and even purchased at some of the big box auto parts stores. I would get a spark plug from a known good source like the dealership and compare it to those.
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05-13-2020, 11:14 AM | #5 |
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Yeah, this is why i asked if then plugs were original, and if not, if he used a ujoint per the manual. The car only has 26k miles so its possible they were the original plugs. Lots of threads recently of people cracking the ceramic by using only a straight extension.
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05-13-2020, 12:01 PM | #6 |
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Plugs are new, less than 500 miles, OEM NGK SILZKBR8D8S. Purchased from FPC Euro about a month ago.
They were removed by my mechanic and inspected when I brought the car in, then reinstalled, after he verified their was no weird marking or burn on each one. Later, on one of the test drives after doing all the DME reprogramming, the car super knocked at the usual 5K-ish rpm's... and when they limped it back to the shop, what you see in that picture is what they found. They can recreate the almost every time, by driving the car around for about 10 minutes to get the IATs up to full normal temps, and then accelerate to about 4.5K or 5K rpms. The car feels like it hits a wall, as typically all but one cylinder is shutdown by the DME. Here is what the borescope saw after the spark plug was removed. I'm just not convinced that the piston made actual physical contact with the piston. Seems to me that maybe scarring like that can happen with pre-ignition also? |
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05-13-2020, 12:11 PM | #7 |
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So it's still not clear to me, were there any issues (including this "super knock") before you changed the plugs? Or did it all start after the plug change?
I still think, as others have suggested as well, that the plug was cracked during install (or removal and reinstallation). The damage shown in the picture could have then occurred as a result. There was another thread recently where someone broke the ceramic on their plug and got debris into the cylinders. I don't see how the piston could have hit the spark plug... but that mark does not look like detonation/knock; that is usually small pitting, not a clear mark like that. |
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05-13-2020, 01:08 PM | #8 | |
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05-13-2020, 01:48 PM | #9 |
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The piston can't contact the plug. It can't contact a valve either, the valve timing would have to be so far off that the engine wouldn't run.
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05-13-2020, 02:53 PM | #10 | |
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If the piston is coming up more than design, you do have issues, big problems. Pre-ignition does cause more heat, but wouldn't expect enough heat to damage the plug ceramic. But you can't rule it out. BTW, the plug doesn't look to have overheated from the picture posted. |
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05-14-2020, 09:55 AM | #12 | |
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Just got these borescope pics... not sure what to make of them yet. |
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05-14-2020, 10:26 AM | #13 |
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And the leak-down test showed 30% loss in both cylinder 1 & 2
The compression test had me hopeful that there was no cylinder or piston related issues... but that hope is fading away. Considering that the previous owner ran the car on 89 octane, I can only assume that they also didn't bother with oil changes. Or they used cheap oil not to BMW specs. My mechanic actually mentioned he was surprised how dark it was already, as the dealership that I bought it from would have changed it before selling it. Not sure if I'm screwed or not... yet! Last edited by wesmeister; 05-14-2020 at 11:25 AM.. |
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05-14-2020, 12:22 PM | #14 |
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This seems weird. And those boroscope pics are pretty bad, normally you can get a much clearer imagine. Maybe go in and see for yourself on the live camera?
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05-14-2020, 01:06 PM | #15 | |
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05-14-2020, 01:24 PM | #16 | |
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Changed 26k mile plugs on a stock car? Then plug mysteriously destroyed and blamed on knock and not a botched install? Weird marks on pistons and unclear boroscope of cylinder walls... compression looks good at first but then later leakdown fails... Do you trust this shop? |
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05-14-2020, 03:35 PM | #17 | |
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OP, did you change the plugs yourself, or did someone else? |
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05-14-2020, 06:21 PM | #18 | |
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I bought these exact plugs: https://www.fcpeuro.com/products/bmw...plug-ngk-96987 The car had a rough idle when I bought it. The plugs were changed as part of a regular tune-up I did myself, to include new OEM oil filter, air filter, and Liqui Molly 5w-30. |
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05-14-2020, 06:34 PM | #19 | |
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05-14-2020, 06:53 PM | #20 | |
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Rings are definitely a consideration at this point , but are going to require a tear-down to inspect. The borescope didn't show any immediate damage to the compression rings. It could be a serious blow-by problem from lower rings... which could then, in theory, amplify this super knock condition once the IATs get high. Ah yes, warranty. I bought the car "as-is" from a BMW dealership. It had the typical 75 point inspection and looked good mechanically and aesthetically when I purchased it. I went ahead with an aftermarket warranty from the dealership, that BMW honors at all of their dealerships. The car might end up back there, depending on what my mechanic finds next... Sure I trust this mechanic shop. They are one of the best independent BMW shops in Southern California. They are being very pragmatic and working with BMW tech support directly through ISTA+ on the diagnosis. But I think it's safe to say that this case is highly unusual, so I thought I'd start a thread to see if anyone has any insights out there. Again, if anyone is interested in helping with a little more "arm-chair mechanic" analysis... I have the diagnosis report online I can share PM. I just don't want to plaster that link on the internet. |
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05-14-2020, 06:59 PM | #21 | |
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So basically, it has gotten worse with time. Irrespective of the new spark plugs. The new spark plugs DID help ease the rough idle though |
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05-14-2020, 07:14 PM | #22 | |
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