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Old 06-06-2012, 11:14 PM   #1
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I am somewhat new to tuning and working on cars. I'm rebuilding a wrecked 92 Miata.

I was reading about detonation tonight and it mentioned hearing rattles. I occasionally have rattles up front that possibly sound engine related that I can't seem to find. It then mentioned checking plugs for flecks of carbon and aluminum.

I haven't checked the plugs since I got the car so I thought I better take a look. I took out one and it was a little moist on the bottom half with silver colored liquid. I took some pictures, see below.

Is this detonation, something else, or normal?

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Old 06-06-2012, 11:22 PM   #2
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Hard to tell from the pics, you need some close up macro shots of the electrode area.

The coloring looks ok, not too white. They do look old though, you can see the yellowing around the porcelain in the middle.
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Old 06-06-2012, 11:32 PM   #3
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Really hard to tell from the pictures, take some close ups from a top view.
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Old 06-06-2012, 11:36 PM   #4
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Ok. I'll get some better pictures tomorrow. Here are the same pictures, cropped, zoomed, brightened...

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Old 06-06-2012, 11:42 PM   #5
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"Rattles" is a bit vague, but the early Miatas are notorious for having extremely loud hydraulic lash adjuster (valve lifters.) They're loudest when the oil is cold, quiet down a bit as the engine gets warm, and then get loud again as the oil becomes very hot. The noise can range from a slight tapping sound to something resembling an anti-aircraft gun being fired at a cement-mixer filled with hammers being dragged down a field of boulders by a diesel truck.

Your plug looks fine to me, by the way. I can't really see the "silver-colored liquid" of which you speak. Could it be anti-seize compound? It's silver, a liquid, and is commonly found on the lower portion of spark plugs.
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Old 06-06-2012, 11:50 PM   #6
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I guess the sound is more like a metallic buzzing. I have a video. Actually more audio than video. You can hear it a few times throughout the clip, but I think it is most noticeable in the last few seconds.

Normally it happens in 2nd or 3rd, 2500-4000rpm. If I change throttle pressure up or down it usually goes away.
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Old 06-07-2012, 01:06 AM   #7
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I think you're OK. If anything, the plugs show you're running a little rich -- which is safe.

Usually a rattle like you describe would be something loose with the exhaust system. Perhaps a shield isn't secure or a nut somewhere has backed off.
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Old 06-07-2012, 01:13 AM   #8
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2 things:
1: I have never seen anybody upload a youtube video that was only sound. Ray Charles would approve.
2: You mentioned metallic rattle. Are you thinking you may be experiencing detonation or a misfire because of your plugs? Personally, I don't think they look bad enough to cause that kind of problem. Replace them since you have em out, or wire brush them and then check the gaps.
What plugs are they, and what gap were you running?
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Old 06-07-2012, 01:51 AM   #9
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if its misfiring it's more likely plug wires then plugs. plugs look fine to me and our cars are known to have sensitive/weak plug wires. does not mean that's what's causing your noise though. I can't tell from the youtube if it's actually misfiring.
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Old 06-07-2012, 01:53 AM   #10
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Quote:
Originally Posted by Joe Perez View Post
something resembling an anti-aircraft gun being fired at a cement-mixer filled with hammers being dragged down a field of boulders by a diesel truck.
Best description I have ever heard, about anything, ever.
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Old 06-07-2012, 07:04 AM   #11
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I'm probably just paranoid. I don't know that there are any misfires or detonation, but I don't know enough to confirm.

The plugs are NGK BKRE6S 11. No idea on the gap since they came with the car and I haven't checked.
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Old 06-07-2012, 09:27 PM   #12
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I took plugs 1 and 2 out and got some hopefully better pictures. Notice the deposits or something on #2. Would that be what bits of piston look like from detonation?

Plug #1


Plug #2
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Old 06-07-2012, 10:05 PM   #13
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They look pretty good. You have a nice solid black ring at the end of the threads indicating a slightly rich condition (good for turbos).

Most of us with F.I. run ngk 7's, it's a step cooler plug over what you're running.
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Old 06-07-2012, 10:54 PM   #14
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Absolutely nothing wrong with those plugs.

Heavy detonation results in damaged (chipped) ceramics -- sometimes even a broken electrode.

The thing you are thinking about is pre-ignition due to overheated plugs. When that happens, the result on power is dramatic (like 50% less, runs like #$%@). Also, the appearance of the plugs is unique, they will be completely clean as if they just came out of the box and the ceramic will have little black dots in it. Both of these are the result of overheating.

Relax. Have you tracked down your loose exhaust shield yet?
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Old 06-08-2012, 12:29 AM   #15
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You'll want to switch to BKR7Es soon. They handle 8+ psi better than the 6's.
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Old 06-08-2012, 04:15 PM   #16
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Thanks for your help guys.
I went searching for the rattle/buzzing today, and I found a few things....

Can't get to bolt "A" on the bottom of the exhaust. Transmission and dipstick and a couple other things in the way. Coolant leak, "B", but I can't trace it to either side. Could the hose itself be cracked behind the steel?


I removed the heat shields, ignore the ungrounded cable. It looks like these two bolts, "C" and "D", might actually be broken?


Another loose bolt "E" near the exhaust.


Picture of bolts "E" and "A".
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Old 06-09-2012, 01:57 AM   #17
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Bingo!!

BTW, your car will run better once you get all that stuff buttoned up. Search threads for "inconel," "epic stud," and "safety wire" for ideas.
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Old 06-09-2012, 08:35 PM   #18
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The coolant leak looks to be from your feed or return line for the turbo, best fix it fast.
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Old 06-09-2012, 11:00 PM   #19
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I replaced the two studs on the back of the manifold/turbo. I had an exhaust leak there that I wasn't aware of until I removed the heat shields and felt the air blowing yesterday.




After adding two new studs the leak if pretty much, if not completely, gone.

I was able to tighten the turbo support bolt labeled "E" in a picture in a previous post.

I was not able to tighten bolt "A" on the bottom-right of the downpipe. The other three bolts are solid tight.

The original rattles are gone. There is a new one now. I think it might be the heat shields around the turbo.
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