Hi guys. I have noticed that when I press full throttle, and above 4K rpm, the exhaust make some not normal "bang bang" sounds and the engine lose power for the very little duration of each bang. It does not show any codes or lights, but when i check with Torque, it seems that there are some missfires at cylinder 1 mostly (10-20 missfires), and at cylinder 4 (5-8).

The car is cooper S r56, it has 40 000 miles, I use 98 Octane gas and i have decarbon the valves by myself 5000 miles ago by removing the manifold. There are no mods, just an K&N filter. Also the air temperature is about 100 degrees Farenheit.

I am thinking that the sparkplugs might not working correctly, but I would like to know any thougts why this happens, and any solutions.
Thnx

 

98 octane? Where do you live?

Is the sound really a bang? When i think of a bang I'm thinking of a loud shotgun noise coming out your exhaust. Are you sure you're not hearing the sound of pining/detonation?

 

In Europe. I think we have different measurment system. Our 98 Octane is like 93 Octane in USA, and ours 95 is yours 91. Not 100% sure about this.

I can't describe the sound, but I am pretty sure there are not "normal" exhaust pops and bangs. It is like small explosions, or gunfire or like some gas passed to the exhaust and detonated in the rear muffler. Not very loud but you can hear them with closed windows and the engine running at 4- 5K rpm. I think its being called Backfire?

 

MON/RON are measured differently so yes, it is like our 93 here. This is happening on acceleration?

 

On hard acceleration and only when the pedal is fully pressed, and the engine goes above 4K. When you are doing normal driving, it doesent happened.

 

I would start with the plugs and start working my way out. Check the gap and make sure they are clean.

 

I made some logs using torque and it seems that the fuel pump is working fine. It can go up to 1680 psi at 5500 rpm. Also the fact that the misfires don't happen in random cylinders, also points to that. Also the turbo boost seems stable at 15.1 psi at this rpm.

So I am guessing it might be the sparkplugs, the spark plug wires, or something electrical related to that.

I am going to order 4 NGK Iridium Spark Plug ILZKBR7A-8G, to start with and then I will see.

Can the spark plug, or the wires, fail in 40000 miles? arent they supposed to hold until 100 000?

 

if you get alot of carbon on a plug it can fail to fire. I am at 106k and on my 3rd set of plugs, i change them right around 40k and did the most recent set just because.

 

What year is your MCS? Bet your vehicle is in need of carbon cleaning service as well as a full vehicle encoding/module update. Misfires (especially in cyl 1 & 4 which are companion cylinders) and loss of power in higher RPM range is a good sign as well. Do you notice your vehicle idles rough @ cold starts (first fire up of the morning or day?)? Try cold starting your vehicle (allow it to sit for a full 10-12 hours) and once you get it fired up, step on the accelerator and rev it up to 5k a couple times in a row and have someone stand and view your exhaust (or look in your rear view mirror if its really bad you'll see it) but if you see allot of black smoke or smoke in general, its probably another good sign you need to get your intake runners and backsides of your intake valves cleaned up.

It is also possible that your vehicles timing mechanism is failing as well, though I cant be sure so my statement here is a random shot in the dark, though misfires can also be caused by a over stretched timing chain. Thats why I ask what year your vehicle is, as well has it ever had its timing chain assembly inspected (tensioner, chain, guides). Usually plugs do not foul out in 40k but as a good practice I usually recommend replacement of them, especially for turbo cars (MINI says 100k...yeah don't ride that).

 

It's a UK car, manufactured October 2007 with auto start/stop. I took it used 1.5 year ago. Before me the services were done to Mini, and the service history doesnt have anything about tensioner or software update. After I took it, I do the services with my uncle which is a mechanic, because the Mini service here is a rip off. They want $100 even if the car has nothing. Also I took it there to change the water pump (recall), they inspected the car, they told me that some stupid things need to be changed and blablabla but didn't say anything about update. I am pretty sure, if it needed an update, they would mention it just to take the extra money.

About the cold start, I try the method you said, the car worked perfectly. No misfires, no strange sounds, no smoke or anything (I think). I will try and make a recording tonight and upload it to tell me your opinions. About the carbon, I used a carbon cleaner that you put in the fuel, and then I hand cleaned the valves. Not perfect job but much better (visually) than before, even that I didnt notice anything after. You can see the pics. I might even do it again in a month.


As I said before, the car works and sounds perfectly. Only problem is when you fully press the gas, at 4K rpm and up makes 10-15 (until you change gear) pops/ bangs from the rear muffler, and at the brief time of each bang, the engine loose power. Not a continue lost at high rpm. Just for very brief moments. Not very big power loss. You barely feel it.

The car need service in 1.5K miles, so I am searching to see what I might need to check or change to fix it.

 

I made some recordings. I dont know how to upload wav files, so I put them in a zip, and put them here ( i dont know if its against forum rules)

http://depositfiles.com/files/krhik61aq (4mb, 2 .wav files in a zip folder)

Its a file with the cold start up, and one with the sounds i am trying to describe.