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Old 07-03-2008, 12:39 AM
mrdjsk's Avatar
Join Date: May 2008
Location: New York
Posts: 190
Smoke at full throttle

My engine (OM617 turbo) is throwing out a fair amount of black smoke at full throttle on the highway. Under normal conditions though, smoke is not obvious either visibly or by smell.

What does this indicate and what can I do, if anything, to minimize it?

The car is a 1983 California 300D Turbo that drives wonderfully. Good fuel economy, decent power, no oil consumption to speak of.

Thanks for any insight out there.

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Old 07-03-2008, 12:46 AM
Posts: n/a
Is the air filter clean?
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Old 07-03-2008, 12:49 AM
Registered User
Join Date: Dec 2005
Location: Carson City, NV
Posts: 3,786
Black smoke is from partially burned fuel. You get it when the amount of fuel in the cylinder is too much to fully combust with the available air.

Is this black smoke for a few seconds when first flooring it, or does it continue to smoke as long as you keep it floored? If the former, your ALDA could have been tuned to "smoky" by a previous owner. If the latter, you probably have something limiting your airflow. This is most commonly caused by a dirty air filter, but can also result from trouble with the turbo or wastegate. Also, and this doesn't happen much on Mercedes diesels, your intake manifold could be sufficiently crudded up from the EGR that it's significantly restricting airflow. You see that much more often on newer VW diesels.
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 362,xxx miles
08 Triumph Street Triple 30,xxx miles, lowered 10mm in front, Pirelli Angel GT tires, EBC HH brake pads, otherwise stock.
88 Jaguar XJS V12 92,xxx miles. I should be in the garage now.
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Old 07-03-2008, 01:52 AM
compress ignite's Avatar
Drone aspiring to Serfdom
Join Date: Feb 2004
Location: 32(degrees) North by 81(degrees) West
Posts: 5,554
How many Miles?

When did you last change the air filter?
Black smoke at full throttle is usually too much fuel (Unburned)
(Unless you let it "idle" for excessive times...even then "Running It" "Italian
Tuneup" would take care of some of the carbon and coking)
[I will not suggest WOT throttle operation on an older engine that has not
been FULLY checked out by a competent Mercedes Specialist ...too much
chance of BAD NEWS]
Do you use Redline Synthetic Diesel Fuel Catlyst?


I see Craig and Skippy have beat me to almost all of it.
'84 300SD sold
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Old 07-03-2008, 12:25 PM
mrdjsk's Avatar
Join Date: May 2008
Location: New York
Posts: 190
Makes perfect sense

Yes, unburnt fuel. That makes perfect sense. I'll blow out the air filter and see if improving that part of the equation makes a difference.
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Old 07-03-2008, 12:34 PM
vstech's Avatar
Join Date: Mar 2006
Location: Mount Holly, NC
Posts: 26,345
if the filter is dirty, you will not be able to "blow it out" much... just get a new one... $10 just about anywhere... oh wait.. california car... don't tell me you have the cali ash can air filter.... ooooooooh nooooooooo! to quote mr bill...

John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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