Which code do you have? AA or AB.
Also, it's a UK spec car, and if I am correct would be highly unlikely that it's carbon build up.
I am a bit baffled too. I know that euro gas is better, but CBU is engine design, I was guessing. I find it hard to believe that a euro engine could not get CBU. I do have a way to test to see if the air going in the pump comes out the tailpipes. Complete the test then you know for sure.I was under the impression that the on reason this is true is that US spec cars will set the MIL/CEL light for an AA code, but OUS the code may occur but is 'silent' (ie does not set the light.)
The bad design is the SAI tube that connects the two exhaust manifolds. It allows flow of carbon in the exhaust gas to pass through it while equalizing the pressure. Don't think I understand what you mean "contradictory". Obviously the HC is where the carbon comes from. Could also be driving conditions or practices. More than likely it is the software in the north American car and this tube that connects the banks. Specifically how the DME responds to our tighter emission standards. NOx control is the issue that would move the exhaust back and forth through the SAI tube. It may not be as strong in the Euro cars.I see your point guys, but I have yet to see anyone on the board (unless I have missed it) that has a Euro spec car with this issue.
Your statement about engine design and fuel is contradictory by the way, without fuel you don't get carbon, i think it is fair to consider that fuel may be the issue and not the engine itself, but I welcome any discussion on this.