Diesel Gent,

What kind of smoking did you have? Was it blue, white or black? Blue is usually engine oil, white can be engine oil in huge quantities or engine coolant, and black is typically excess fuel.

Without a few more clues there are too many plausible ideas that can be brought up, with only one of them being the correct one to be helpful. Unchecked this usually leads to a bunch of fiddling with stuff that is ok, which can result in breaking otherwise serviceable parts while you investigate a bunch of red herring ideas. This also ends up costing you money while you replace these inadvertently broken parts along the way to finding the real problem.

If you could describe the knocking it would help too. There are a bunch of typical, regular, synchronized noises from a Diesel that, as long as they remain orderly and regular are fine. Then there are other irregular noises, that are not fine and indicate problems. Typically significant changes in the noise levels or other characteristics are not good signs. Then, sometimes they are pretty straightforward things like air cleaner mounts or manifold fasteners coming loose.

Good luck and hope to hear a few more details. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)