I posted a seafoaming thread a week ago and SoCal MCS suggested that I replace the plugs. I was skeptical since I have never actually seen a plug fail. Usually if the plug isn't operating correctly it is because it is fouled for some reason other then the plug but I am willing to try anything. This is what I found. What would cause this type of damage? It does not seem like standard wear and tear. The plugs are arranged in cylinder order. Would the dealership not have noticed something 6 months ago when they tried to diagnose my severe hesitation and recommended (and performed) the extremely expensive walnut blasting?

 

That is what preingnition/knock does to your spark plugs. That is why it is important to run the right octane in your car.

 

It appears to be PreIgnition. You can tell by the melted electrodes. This might indicate engine damage. This can be caused by the wrong type of fuel, incorrect ignition timing and advance, too hot a plug, engine overheating or burnt valves.
I would highly suggest that you decarbonize the combustion chamber before installing new spark plugs. Just my opinion

 

Thanks for the suggestions. I have always run Chevron or Quicktrip hi-test fuel. The plugs were the factory plugs and I have replaced with the same. According to the Bentley manual ignition timing is not adjustable. I had a leakdown test at the dealer and according to them cylinder two is the worst at 16% (three is the burnt one). In looking back at my service for the walnut blasting there is a note that says "Note #3 spark plug hole getting on in it". I have no idea what that means.

How does one decarbonize the combustion chamber?

 

By walnut blasting.
This does nothing on a direct injection motor. With direct injection, fuel is injected directly into the cylinders and never comes in contact with the tracts and valves of the intake. Because of this modern injection style and lack of clean fuel in the intake, blow-by gasses that travel through the intake create deposits. Although blow-by gases consist primarily of air, small amounts of oil and exhaust particles do exist and contribute to dirty intake tracts and valves. This buildup is referred to as carbonization.

 

Well #3 looks wet which is most likely caused by the plug misfiring and not burning off the fuel...to be expected based on the photo.

I totally agree with some of the other comments already stated but there is one more to add to the list....incorrect plug gap when the plug was installed. By replacing the plugs which you have done this should no longer be an issue. Since #3 has not been performing for a while, carbon buildup is highly likely as well. I forgot if you had the blast done, other than the cryptic comment in your records, but I would have it done. Most shops than can do it are happy to take before/after photos so you can see that they are nice and shiny.

I had a valve seat fail which caused me to replace all the seats and valve guides (warranty paid) but the cylinder that was affected did not have a plug issue. The seat that failed was incorrectly installed at the factory that created a hot spot on the valve...see thread called "Dropped Valve".

 

I did have the blasting done but I have my doubt whether the labor was actually performed or performed correctly since they didn't notice the destroyed sparkplug. I have friend with a boroscope so I will have to have him bring it over to take a look or I'll just open it up. Here's to hoping the problem is fixed for good.

 

Amen!

Hope it all works out so you can motor in peace!

 

I second that. Keep us posted.

 

Your walnut blasting is done pre-combustion chamber. All it does is clean the top of the valves and the intake runners. You would have to remove the head to actually clean the inside of the chamber.

That looks like minor detonation. I would try new plugs and check them after a few hundred miles. If the problem persists, you might have other underlying issues. A set of plugs to help diagnose the issue, is cheaper than having a shop try to figure it out.

Good luck!

 

What octane fuel are you using? If you're using less than 91, make sure you're using 91 or above. If you're already using 91, then you'll have to do some more digging. Saving $2.60 (20 cent difference on 13 gallons) on a tank of gas isn't worth it!

Also make sure the spark plugs are right. They might be the wrong application.

 

The combustion chamber is the area inside the engine where the fuel/air mixture is compressed and then ignited. It is generally formed on one side by the shape cast into the cylinder head, and on the other side by the top of the piston

http://www.youtube.com/watch?v=R-HlW...ature=youtu.be

 

Exactly. Walnut blasting doesn't do anything to the combustion chamber. It's only on the intake runners and the top of the intake valves. The picture above shows what is blasted.

Since our motors are direct injected, fuel is injected directly into the combustion chamber, hence the build up of carbon on the valves. When the walnut blasting is done, the motor is rotated to close the valves on each port, so that walnut sediment isn't forced into the combustion chamber.

 

Look more closely--could it say "OIL" intead of "on"?

 

As indicated above, My take on this is get new plugs, gap and torque them right, drive for a couple hundred miles and check them. This looks like ping damage to the plug. How many miles on plugs? The other plugs look "normal" to my non-expert eye (not oily, not burned)

You have an '07 MCS, same as ours. We had walnut blasting done 5k miles ago at 30k miles, along with a reprogram. I talked to the tech and he indicated that the new program they install following the blast is less aggressive on the timing to control ping during certain situations.

The indication we needed walnut blast was a check engine light that came on (at the end), but weak-ish acceleration along with occasional pinging (despite running chevron 91, always)

It's very possible your carbon build up was causing ping issues that destroyed the plug. You've had a walnut blast done, swap the plug and see what happens.

 

The high leakdown rate makes sense for #3 cylinder. The spark plug has not been firing for a while, and unfortunately that means that the raw fuel has been washing down the cylinder, which will wear the rings quickly. I would think that the oxygen sensor would then sense the raw fuel in the exhaust, and lean out all cylinders, which could create your hesitation.

New plugs should make an immediate improvement, but 16% leakage is quite a bit. See how it runs with the new plugs. There are others that are more familiar with the details of the MINI drivetrain.

Mike