Hi all I am stumped the other day I was driving my 1.9 multijet diesel and all of a sudden I had a very loud engine knock and a sudden thick black smoke coming from the exhaust so I did some research and found it could possible be a bad injector which was overfueling the cylinder so I had it checked out did a leak off test and the number four injector was pumping in over the 20% more fuel than the rest so I got a new injector and had it replaced which has helped slightly reduced the black smoke in idle but still loads when accelerating plus I still have the loud engine knock so if anyone has any ideas or had similar problem i would love to hear them