Reading Exhaust Smoke, basic Diesel diagnosis/Troubleshooting + related comments - PeachParts Mercedes-Benz Forum

whunter · #1 02-14-2013, 07:27 PM

This one is strange enough for special note...

At the end of my patience-1984 300D issue

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BLUE SMOKE

* Excessive blue smoke usually indicates low piston cylinder compression, commonly caused by crankcase oil entering the combustion chamber, partial combustion, then out the exhaust.
* Worn piston rings.
* Scored cylinder wall.
* Valve guide/seal leak.
* Head gasket failure on an oil passage to cylinder.

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WHITE SMOKE smells like diesel:
Note: If slow cranking is not the problem !!!

* Air in the fuel system.
* Seriously contaminated or extreme (critically) low cetane diesel can cause white smoke.
* Valves out of adjustment (OM615, OM616, OM617 and all earlier diesel engines).
* Depending upon your ambient temperature, bad glow plugs or a faulty glow plug control module can cause or exacerbate white smoke during engine cold start up.
* Dirty injectors lean out the air/fuel mixture, causing loss of power, rough idle and sometimes, white exhaust smoke.
* When white smoke is still visible after full operating temperature, the engine may have one or more bad injectors, miss adjusted ALDA, retarded injection timing, a damaged timing device, or a worn/damaged injection pump.
* Low engine cylinder compression.
White smoke generally happens when there is not enough heat to burn the fuel.
The unburnt fuel particles blow out the tailpipe producing a rich, thick, diesel fuel odor.
It is normal to see white smoke from the exhaust during sub-zero and colder weather, at least until the engine warms up.

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WHITE SMOKE no diesel, or cloying sweet odor:

* Typically a coolant leak into one or more combustion chamber.
* Cracked head, bad head gasket, cracked cylinder.
* Usually a cooling system pressure test will eliminate all possible external issues, leaving mechanical diagnostic engine teardown the only option.

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BLACK SMOKE

* Black smoke is usually a sign that there's too much fuel, not enough air or injection pump timing is off.
* Leaky injectors will enrich the air/fuel mixture and cause black smoke.
* A restricted exhaust system.
* Leaking Turbo seal.
* Worn - damaged valve guides and or seals.
* Vacuum modulator diaphragm broken = transmission fluid pumping into the engine crankcase through the vacuum pump = potential engine runaway (please read this for more on this topic)

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Mechanical diesel injector failure has TWO root causes:
1. Fuel contamination/quality.
2. Structural failure.

MECHANICAL DIESEL INJECTOR PROBLEMS

X. varnish deposits.
X. Obstruction - Clogging.
X. Wear - erosion.
X. Leakage.
X. Weak spring - age.

You need a pop tester to check the opening pressure of the injectors for proper diagnostics..

IMO: The easiest way to find a seriously bad injector on a mechanical injection diesel is to loosen one line at a time with the engine running.
General Note: If while changing the glow plugs the ends are burned, check the injection timing because may be advanced to far.

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