Hi,
And first of all I know there is many topics about this and i have read them many times but no use to me so lets see.

As title says my S has lost its power, topspeed dropped from 240 to 200 and acceleration from 80 to 120 is now with 3 gear same as it was before with 4 gear.
At somepoint I am sure i need to go to the dealer but as i know they will change parts after parts bill me those and never get fixed the problem and I would first like to do everything i can myself.

Symptoms here is as said before lowered topspeed and acceleration. When accelerating with 1 gear it feels normal so long as u dont press pedal more than 1/2 and when u put it in the floor it first feels that now we gonna go but then it slows down and might then accelerate again and it goes like this to the redline. Another option is when you accelerate from zero it feels again good and then it feels like u would hit the redline and the limiter hits on even you are not even close to that. When this happens the speed is not much but sound from the exhaust is loud. Maybe louder than normal.

2 gear feels ok just slower and missfires sometimes, new plugs are just waiting for install but i know this wont solve the whole problem as i have had this longer now and changed the plugs already year ago and it did solve the missfire thing but nothing else.

3 gear slower but no anything other special.

4, 5 ,6 gear when starting to accelerate from 80 with full throttle i can feel light stutter and vibration and tachometer needle doesnt move smoothly but goes forward with little steps. With 4 gear this will end when speed goes over 100 and also acceleration might feel to increase a bit. Maybe its not related to speed but more revs and when u get over 3000-3500 it goes bit better.
Also when I feel stutter etc and lift some gas it ends and it feels like it would accelerate better.

Idle is good, runs ok, only at cold start its a bit rough for a minute but nothing special in there too. It just passed vehicle inspection, emission tests and OBD diagnostic tests. No check engine light or fault codes. It has been in service too and they never said anything would be wrong.
Also when this started i thought that dealer has been reprogrammed it and overwrite ecutune but my ecutuner said its ok and they also red codes from OBD and nothing was there.

So this is somehow frustrating now and i hope someone here could know something.

Now I am not mechanic but made a conclusion it might not be any electrical issue but maybe more likely some mechanical thing so what could lead to this?

Now I have been searching info of carbon buildup and found this http://www.bobistheoilguy.com/forums...1612850&page=1
So obviously I am thinking could this be performed? I know it has major risks and does anyone have knowledge or even experience of doing that?
Could it be done via the pcv hose if done?

Maybe here is all for now and i truly hope someone could lead me some maybe right direction

 

You've posted a long report, but do you have any empirical data to back-up your thoughts?
Have you scanned the ECU with a Bavarian Technic scanner to see if there's any faults?
Have you data logged your knock voltages, MAF readings, fuel trim, etc, etc?
Have you measured fuel pressure from the high pressure fuel pump to the specifications of the service manual?

It's hard to pinpoint a single issue when there's SEVERAL variables involved and there's no proof / data of what's been tested and verified.
Yes, there's some work ahead of you to check a few things out first, but that will hone in on your possible issues at hand.

- Erik

 

I would have suspected the plugs as I had a similar problem, replacing mine sorted the problem though. So I would get the coil pack checked out but like Erik mentioned your best bet is to have a diagnosis done to check for any misfire in the cylinders. And then to clear the code and swap the coil packs around.

eg. If misfire detected in cylinder 1, move that coil pack to cylinder 4 and clear code before you start. Fire up and see if the misfire now moves to cylinder 4. If so then its your coil pack.

I would get another OBD scanner as again I had a similar problem, the first model I used gave no error codes, I ended up with getting another extensive one done and all the above showed up.

As you also pointed out Carbon build up is a problem with the r56 so I would pop the manifold open and have a look down the chambers to see how caked they are.

Judging by the speeds you seem to be doing 200-240 I'm hoping you in Germany (autobahn) if so I am sure you can get hold of some good carb cleaner.

Last resort your HPFP could be going out.

 

I had stumbling between ~2900 - 3400 rpm in 3rd and 4th gear (where I do most of my driving). 4 tanks of adding Techron gas additive helped a little, but did not restore the performance I had experienced when I bought my car with 30k miles on it. Once I cleaned the carbon build-up off my intake valves (at ~46k miles, filling the tank with nothing but 91 octane gas since I bought the car at 30k miles), I can hardly hold on to the steeting wheel (due to torque steer)! A dramatic improvement!
How many miles on your car? What are your driving habits ("Driving Miss Daisy or Mad Max")? From what I have read, the MCS likes to be rev'ed. And since I started driving my '07 MCS this way (prior to the intake valve cleaning) it responded in-kind. Of course, this could have been due-to crap build-up in the fuel injectors which is why I saw some performance improvement after 4 Techron gas treatments.
Anyway, keep doing some searches in this forum...lots of info here and the members are tremendously helpful!
Good Luck!

 

another vote for carbon build-up. I just finished cleaning the valves and WOW, what a difference. Ours ran rough when cold and stumbled in the higher gears. Now it purrs like a kitten. Dealers or shops will clean them for $500-600, or you can search here and do it yourself for close to nothing.

 

Yes, I actually did that months ago and its so amazing that so little thing can cause so much trouble. Actually I have done it already 3 times as i did not get them as shiny as i want to get them so i try to figure it out what would be the best solution as like easy an effective. Blasting with soda seems to be good though its a bit messy.

I first took it to the shop who had tuned ecu but they searched a week for the problem and didn find it so has to be done by myself:P

Then they put new a bit more powerfull tune in it and now she almost flys, even now i have other problem:D
When hitting full throttle i sometimes i get this tsktsktsk sound or a rattle or however i could describe it and again drops some power, not much but it has little bit stutter/strugle and after the sound stops we go again.
That never happens more than once in acceleration and usually it doesn affect much but sometimes its so bad it it drops power almost all for a very little time and gets kind of buff sound from exhaust and then its ok again.

So i have searched and came to a conclusion that this tsktsktsk sound could be something to do with knocking and knock sensor so if someone can point me a bit to some direction with this and I would appreciate that

Anyway i am getting good for the intake manifold ripping so if someone wants hints or tips how to clean valves I could surely help with that:P

-Susihukka-

 

Holy cow, there was much more answers than i knew as i never got any notification mail.

So much of thanks for everyone who gave advice and spent their time with this

Anyhow first problem solved and new one came:D Or i dont know if those are related but now it went even worse
So its ok if i drive gently but if i hit the gas suddenly all power is gone and it dumps all boost from dump valve and then engine starts to rev up and down between 1000-1200rpm on idlle. Usually i do it myself in street lights but now i don need:P
Also it gets this reduced power light in the tachometer but if i stop the engine and start it again all goes away until i again accelerate.

Good thing is that I now have check engine light so maybe now there would be some code to give some information:D
I think of buying Scangauge2 for getting those codes read and also to get some other information that it gives.
Has anyone any experince of that SG2? is it good for that?

Also Could this finally be the HPFP? Car starts very well so it doesn sound like that but maybe?