Wrote the following guide to what can be wrong with a Diesel
based on the color of its exhaust smoke. Just got it transferred
off my laptop so I can post it.

/Martin

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        My diesel smokes, what is wrong?

A correctly tuned VW diesel shouldn't smoke, except for
during cold weather startup (for a short period). The three
colors of smoke one can encounter indicate different problems.

Black, or very dark gray smoke comes from unburned carbon
particles in the exhaust. This kind of smoke is produced
under high load conditions, such as when accelerating or
climbing a hill. Possible causes are:

  1/ Fuel metering too rich. More fuel is supplied than can be
  burned by the oxygen available in the cylinders.

  2/ Fuel injection timing wrong. The fuel is delivered at the
  wrong time, causing incomplete combustion. If injection is
  to late (retarded timing) the engine will smoke most at high
  speed, and will perhaps be somewhat quieter than normal.
  Advanced timing causes smoking at low speeds and a noisier than
  normal engine.

  3/ Dirty injector nozzles. A correctly functioning injector
  distributes the fuel evenly in the cylinder. A dirty or
  worn nozzle may have an uneven spray pattern causing an
  ovely rich mixture in some parts of the cylinder, with
  (locally) incomplete combustion and black smoke as a symptom.

  4/ Dirty airfilter. A dirty airfilter will restrict the
  airflow at high speeds and cause smoking and some powerloss.

Blueish, or blue-gray smoke comes from motor oil leaking past
the rings or valve seals in a worn engine.

  1/ Worn rings: The blue smoke is persistent regardless of
  speed, load and temperature.

  2/ Worn valve seals: Smoke is most evident during acceleration.

White, or very light grey smoke is caused by unburnt fuel
from a misfiring cylinder. A short period of white smoke is
normal after a cold weather start, but any prolonged smoking
indicates a problem.

  1/ Faulty thermostat (or other cooling problem). The engine
  is not allowed to reach normal operating tmperature, and
  runs as if it was just cold started all the time.

  2/ Leaking injectors. If white or light grey smoke is present
  together with knocking noise in a warm engine under light load,
  the injectors are probably not sealing properly during their
  "off" time.

If smoking is intermittent, and independent of load
occationally belching out puffs of black and sometimes
combined with blue and white smoke, sticky injectors is
likely the problem.

/Martin
--
New and used parts for sale:
  http://www.cs.yale.edu/~jag/vw/forsale.html

Westy 1.9l Turbo Diesel
Quantum 1.6l Turbo Diesel

Martin Jagersand                 email: jag@cs.yale.edu
Computer Science Department             jag@cs.rochester.edu
Yale University

        Slow down and visit the VW diesel Westy page:
          WWW: http://www.cs.rochester.edu/u/jag/vw
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