I have had a new two part exhaust fitted to the old manifold exhaust, which has a catalytic converter. Seemed fine for a couple of weeks, local driving. Took it for a run from London to Cambridge on the M11 and the sooty smoke coming out of the exhaust was unbelieveable. It looked like it was on fire. I stopped and checked on the hard shoulder and really could not see anything wrong. The performance was the same, running fine. I wonder if when breaking the seal between the exhaust manifold pipe to fit the new rear sections, soot had been disturbed and dislodged if it had to be hit by a hammer, which had been laying 'dormant' until a good 'blast through' with a long run? I checked with the exhaust supplier and fitters and they said it may be a split turbo pipe, can't see it though. In my manual it said it can be because of an ill fitting exhaust or broken exhaust brackets. Any ideas anybody?