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Old 03-16-2019, 08:48 PM
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Join Date: Nov 2018
Posts: 22
Heavy smoke under load and acceleration

I have a w115 240 D Mercedes 1976 model. It is smoking heavy under acceleration and if you rev the engine in neutral. It burns no oil inbetween oil changes. The injectors have been rebuilt with monarch nozzles. I adjusted the valves about 4 months ago when i purchased the car. I get about 25 miles per gallon. I drive 41 miles a day with half being highway miles going 70 miles per hour. I suspect that befor i purchased the car it was only driven occasionally in town for many years. The car has run smother and with more power over time. I guess this is due to the highway miles. It does not smoke at all during idle. Any suggestions what could be causing the smoke during acceleration? Thanks
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Old 03-16-2019, 10:29 PM
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Join Date: Oct 2013
Location: New Zealand
Posts: 449
Either too much fuel, or not enough air. Check the air filter etc and then look at adjusting the "throttle" travel
1978 300D, 373,000km 617.912, 711.113 5 speed, 160cc superpump, HX30W turbo...not yet legal
1984 240TD>300TD 121,000 miles, *sold*
1977 250 parts car
1977 280> 300D - 500,000km...Daily

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Old 03-17-2019, 01:55 AM
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Join Date: Sep 2007
Location: Long Beach,CA
Posts: 27,004
If your w115 240 D Mercedes 1976 model has a Pneumatic Governor on it the venture system that creates the vacuum to make it operate can be suspect as well as the Governor Diaphragm which gets less flexible and can get holes in it over time.

Also the bore where the throttle arm goes can leak due to elongation of the bore or the seals on it.

If there is less vacuum gets to the Governor it gives you more fuel.

The test in this thread will tell you if there is a vacuum leak in the system but won't tell you if the leak only shows up at high speeds.

Governor Diaphragm Test
74 240d Grey smoke questions

If you have a Diaphragm type Vacuum Pump if the Diaphragm gets a whole in it Oil comes out of it and goes into the intake manifold (there is a tube that goes from the vacuum pump to the intake manifold).
84 300D, 82 Volvo 244Gl Diesel
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Old 03-17-2019, 12:41 PM
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Join Date: Sep 2001
Posts: 611
What color is the smoke? Has the injection pump timing been checked? Air cleaner by chance have too much oil in it?

Nice car...had one, manual w A/C, no sunroof.

Good luck!!!
Does a Caddy stretch? No, but a Mercedes bendz.
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Old 03-17-2019, 12:56 PM
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Join Date: Nov 2018
Posts: 22
The smoke color apears to be soot black. It comes out in large plooms and quickly dissipates. Thanks everyone for you help and suggestions.
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