My Passat 2.5-litre V6 TDI has 110k on clock. Following engine failure, four new camshafts, followers, etc, were fitted. At the same time, six new Bosch injectors were also fitted. On cold start, the engine vibrates lumpily and very noisily with black smoke. Once warmed up the engine is smooth, and car runs well.

Any idea on the cause of problem? A defective fuel pump has been suggested.