My car has been lying in BB Glenmarie for a couple of days now as they try to diagnose and fix the misfiring issue. Apparently mine is the first case they have accepted; couple of days later, anothe 308 came in with the same prognosis (anyone's here?). They have isolated the problem to carbon build-up in the cylinders and need to remove the entire engine to clean it. Here's how it looks:
The four holes in front are stained with carbon. Another few days before it can be ready. Sigh.
I sympathise with you Kenso, no one wants to see their engine dismantled so early in the ownership period.
This carbon build up is actually a problem that has plagued this engine type in the Mini. Just check out the mini forums in the UK and the US. I believe that BMW/Peugeot made some changes to the pcv arrangement in response,however I am also sure that this was done prior to 2009 build engines. In most cases number three cylinder was the most affected by carbon deposits
Do you know what code they found using PPS? Have they stripped down the cylinder head? I ask this because its important to see which valves are gunged up the most to assist them in finding out the root cause.
Did they conduct an emissions test?
Carbon is a naturally occurring byproduct in a combustion engine, it starts as a thin coat of black soot. Many things, like contaminants found in lower grade petrol or petrol that has been contaminated with paraffin bases substitutes, a vehicle that is running rich, oil leaks, faulty EGR systems, faulty PCV systems and short trip driving can lead to excessive carbon buildup.
This buildup can lead to decreased fuel mileage, excessive emissions, hesitation, lack of power, stalling and poor acceleration because the carbon buildup on the vehicles sensors do not allow the computer to properly control the air/fuel mixture, which can lead to even further carbon buildup. And so it progresses on and on until the engine is choked.
Anyway, they now have to figure out why your engine has excessive carbon build up. I hope that when they have your engine stripped down that they check/clean all the sensors.
Fingers crossed for a quick root cause diagnosis