We have a Cooper S R56 on a 56 plate yes it is the turbo engine, it must be a very early one, it's been misfiring for quite sometime and today I've had a good go over it, I swapped spark plugs and coil packs with another R56. And still the same...
The misfire happens between 1000-1500 rpm and if you accelerate gently then try and hold the revs in this band for a few seconds the car starts to misfire and shakes very violently for about 3 secs then it sort of tries to recover itself, but if you blip the throttle and let it hover back down it does it again, this happens every time and in any gear the real spot to get it to happen worse is about 1100 rpm but as I said it can happen anywhere between 1000-1500rpm.
The car drives fine after this and can pull strong to the red line!
When it ran it was great. Only acted up as you mentioned from a cold start. The dealer first de-coked or cleaned the carbon build up. I took it home and it did the same thing the next morning. Fuel injectors and spark plugs were replaced and 2 days later it did the same thing. It was the third trip to the dealer where they replaced the fuel pump and no issues since then. Knock on wood!
I have a 2007 cooper s and i was getting similar problems, i thought my engine was coked up, i used BG44K a few times, was a little better but still persisted. So after much searching on the internet (as you do!) i decided to try the simpler option of better fuel.I started to fill up with shell v power which is 99 RON unlike normal unleaded which is 95 RON, and the results are amazing my car is transformed, the only thing i can suggest is the that the s does not like cheap fuel, higher octane fuel works a dream in my car, would not go back to normal unleaded ever. Give it a try......
My 07 cooper s runs ok its got 45k on the clock. Only thing I can add is like the above poster has said. Try running on super unleaded, a slightly cheaper form of 99 RON fuel is Tesco momentum. I was told to use it by a tuning garage in Essex when they worked on my Fiesta ST.
Make sure you let your tank get as slow as you feel comfortable with before filling up, less dilution of the new fuel with the old fuel and stops any build up of crud at the bottom of the fuel tank. Use 3/4 even 5 tanks of 99 RON fuel and come back and see if it has solved it.
pull the intake back and see if you have carbon build up on the back of the valves. if you do clean it out with a pick and some brakleen. if you can check you fuel pressure after the high pressure fuel pump it should be over 5bar. if its not its your pump, but im pretty sure that a faulty pump will store faults.
AND THIS IS FOR EVERYONE ELSE READING THIS. 1. R56 S UP TO 2012 HAVE DIRECT INJECTION WITH A POOR OIL DELIVERY SYSTEM, 2012 HAVE IMPROVED OIL SYSTEM. THAT MEANS THE FUEL DOES NOT SPRAY THE BACK OF YOUR VALVES AND DOES NOT WASH THE OIL OFF. AND THAT MEANS THAT USING ANY KIND OF INJECTOR CLEANER TO CLEAN YOUR VALVES WILL NOT DO ANYTHING FOR THE BACK OF YOUR VALVES. TO PREVENT THE CARBON BUIDL UP DRIVE YOUR CAR HARD FROM TIME TO TIME. THAT MEANS READLINING IT.
The AutoGuide.com network consists of the largest network of enthusiast-owned enthusiast-operated automotive communities.
AutoGuide.com provides the latest car reviews, auto show coverage, new car prices, and automotive news. The AutoGuide network operates more than 100 automotive forums where our users consult peers for shopping information and advice, and share opinions as a community.