Hey guys. I'm having a very intermittent occurrence (I'm not going to call it a problem yet). Once every few weeks, sometimes longer, I get a slight pop from the exhaust, sometimes with a slight rattle, and a puff of smoke from the tailpipe.

This only happens if I'm at full throttle (usually on an on-ramp to the highway), in the upper part of the rev range (I'd say over 4k rpms) and so far it has only ever happened once per drive. I can floor it again after it happens, and it seems fine. The OBC doesn't throw any codes or warning lights.

The car is a 2008 R56 MCS (N14) 6 speed, bone stock except some cosmetic changes.

Has anyone experienced a similar phenomenon? Any ideas as to what it might be? Do I need to be worried, or preparing my wallet for some major repairs?

Thanks in advance for your help.

 

Sound like super knock. I too have a thread on this concern. For the time being, if you're going to go full throttle with a load, drop down a gear and it shouldn't happen. Have you have the intake valves cleaned? If so, how long ago were they cleaned?

 

Super knock, huh? That sounds intense.

I haven't had the intake valves cleaned but it's on my to-do list. I'm hoping to DIY it sometime before winter. The car just hit 90k miles, so I'm sure it's not a pretty sight in there.

What exactly is "super knock?" A chunk of carbon getting dislodged and pulverized?

 

To super simplify it, you probably have carbon build up on your valves and probably your combustion chambers as well. The carbon heats up and will cause pre-ignition. When you have a full throttle scenario where your turbo is pumping high boost and the cylinder fires before it should you get super knock.

Knock is normal for our cars as they are always finding the best timing for any given scenario. But when your pushing more boost the result is a harsher knock, which can cause engine damage.

I would recommend keeping your gears lower if you're going to go full throttle. That has kept me in the clear for a while. Cleaning the intake valves helped a lot. It wasn't a fix all, but I haven't had it happen for almost a year now after changing how I drive.

Basically dont lug it, drive it like you stole it and you'll do fine!

 

Alright! Thanks for the explanation! That definitely clarified things.

I'll definitely make the walnut blasting a higher priority.

In the meantime, it's always good to have another excuse to give it the old Italian tune-up!

 

When you do the walnut blasting, I'd replace the spark plugs at the same time to cover all the bases.

 

No need to go to the dealer and pay two to three times as much money either, I got mine done for $350 the second time, first time dealer charged me $800 and did a **** poor job to where I had to do it again!

This last time I demanded to see the valves with my own eyes before reinstalling the manifold, what a difference in power! Have you ever had your intake valves walnut blasted before? If not you waited way to long as your super knock indicates.

Don't wait to long as this is more serious than you think! I would have it done immediately. If pieces of carbon broke loose it could scorch your cylinder walls like a sandblaster which has happened to many others here on NAM.

 

I'm not even going to take it to an indie mechanic for the walnut blasting. I've done a bunch of research on this and other forums and I'm in the process of gathering the equipment for a DIY job. I'll let you know how it goes. Hopefully I'll be able to do it in a week or two.

I've never had them done before but I'm the second owner (bought it at 55k miles) so I don't know if the original owner had any carbon cleaning treatments. It's definitely time to do it, I just need a free day to get it done.

 

Well since you have the super knock I'd bet money it's never been done before, you should notice a big difference in performance when it's all said and done! I notice a huge difference after only 63K miles and my Mini does't consume as much oil as the average N14 engine, I consider myself lucky!

 

Couple helpful links...

https://docs.google.com/file/d/0B3Ta...BoTTM5aEE/edit

https://www.northamericanmotoring.co...-cleaning.html

Also, that nut on the bottom of the intake manifold is the hardest part of getting the damn thing off. I went in through the passenger side wheel well to get it, and just left it off. It now takes no time at all to get the intake manifold off, and i've had zero problems with it. Also, as long as you have the wheel well cover off, it's pretty easy to manually crank the engine over from there. I found using wooden skewers (like you'd cook with) was the easiest way to tell if the valves are open or closed. Pop the spark plugs out and drop the skewers straight down. If the skewers are up, the valves are closed. The valves go 1-2-2-1.

 

I managed to carve out some time to do the intake cleaning a few weeks ago, and I'm definitely glad I did it. So far, I've had no traces of super-knock, even at WOT near redline. It's really nice peace of mind, knowing that I don't have super gunked-up valves.

And boy, were they gunked up. I'll try posting before/after shots that I took with my newest toy, a $30 Android compatible LED endoscope.





Before: you can see the valve stem covered in crud, but can't even tell where the valve head begins!





After: Much better!

As far as regained performance goes... it feels exactly the same lol. The engine ran rough for the first couple of second after starting it (I assume the computer was shuffling around, trying to figure out what to do with itself after the surgery). It calmed down quickly and has idled normally since then. I don't really notice any regained horsepower, but maybe my butt dyno just isn't as finely tuned as yours! I don't really mind though, it's still quick enough to be fun, and the peace of mind of having a clean intake system was totally worth the afternoon's worth of work.

I've been tracking my fuel economy for 9 or 10 months, and I'm currently burning through the first full tank since I did the media blasting. I'll update the thread with the results; I'm not crossing my fingers but it would be nice to get another mpg or two out of the engine.

 

Wow! Your intake was bad.