When my diesel powered 1986 pickup had this problem, it was a bad injector pump. Pretty pricey to replace, but solved the problem. Have it looked at by a good diesel mechanic to be sure.

Incomplete combustion. All Mercedes with mechanical injection pumps can suffer from this problem (240D, 300D, 300D Turbo, 300SD, all mercedes diesels 1985 and prior). The issues is typically quite simple: injection timing. Just as you have to adjust the ignition timing in a gasoline engine to make sure the spark occurs at just the right moment, in a sparkless, or diesel, engine, you have to adjust the high-pressure injection of fuel into the cylinder at the proper moment in order to ensure total combustion of all diesel fuel. If injection occurs early, or late (usually the problem on older benzes), not all diesel will be burned resulting in sooty, smoky exhaust that gets dirtier when you press the gas. It is unlikely that you need a new injection pump. The Bosch mechanical units used in benz diesels are extremely stout and often last the life of the vehicle. Do note that these mechanical injection pumps benefit and gain longevity from good lubrication, which used to be provided in part from the sulfur in diesel fuel. With the advent of ultra-low-sulfur fuel in the U.S., many believe these pumps will suffer reduced longevity. This can be avoided by either adding a small quantity of flax seed oil to a full tank of diesel (perhaps a pint or two) or by switching to a biodiesel blend or straight biodiesel (no conversion is required for biodiesel. Only running straight vegetable oil requires special heaters and the like). To correct your injection timing, if you are good mechanically, purchase an overflow pipe drip tube (http://www.samstagsales.com/mercedes.htm#diesel) , a good mercedes diesel manual, and learn how to set the injection timing. But if this scares you in the slightest, as it is a fairly complex procedure, take it to a shop that is good at working on old benzes. MAKE SURE THEY KNOW HOW TO DO THIS - many claim expertise on old benzes, but they lack experience or knowhow on engines with purely mechanical controls such as these old diesel benzes. Why does injection timing become mis-adjusted? Probably the most common reason is stretching of the heavy-duty timing chain in the benz engine (OM 617 in your car). These engines are known to operate in excess of 500,000 miles (1,000,000 in notable cases). Timing chains in a diesel engine, which bear explosive, high-torque forces over and over from the crankshaft every time a cylinder fires, stretch ever-so-slightly over time. Modern engines with electronic controls re-calibrate the engine to account for this slight change over time. Old mechanical engines, like the benz, must be re-calibrated every so often to account for this stretching. In the OM 617 diesel engine, the timing chain drives the injection pump and its related timing device. As the chain stretches, the relationship between the crankshaft (i.e. piston position within the cylinder) and the injection pump timing device starts to change so that the timing device starts becoming delayed with relation to the crankshaft and pistons. Fuel is injected a bit too late for proper, complete combustion; less diesel is burned, less power is produced, more unburned and sooty diesel exits through the exhaust system, and the engine often "lopes" or rocks erratically at idle because of the delayed and and weakened explosions within the cylinders. The number two reason your injection timing is off is that a mechanic who didn't know this procedure well attempted to adjust it. Many have a rough idea of how to adjust injection timing, and jump into the job without following the steps precisely. A Mercedes dealer or shop might tell you they can perform this, and a younger mechanic might rush through the job never having done it before and not following proper procedure. Before taking your diesel to a shop, make certain they are well-versed in working on old benzes, which are very different vehicles than modern benzes. Both splendidly designed, to be sure, but very different beasts altogether.

women with old cars, especially, have to learn all about them!!! i am the proud owner of a 1982 300sd turbo diesel, too. had the same issue with black smoke. mechanic wanted $500. i fixed it with AFC-705 fuel additive from www.algae-x.net excessive black smoke when accelerating was caused by algae growing in the fuel tank. yes, algae can grow in diesel fuel, when the tank's so very old! the chemical additive cost less than 30$. exhaust is clean now, and she purrs like a kitten with over 300,000 miles on her, and gets 30 MPG. they're heavy engines... made of steel before 1985, not aluminum yet. the idol shake is probably just worn motor mount cushions. quick and easy to change. 'course, the shaking could just be from it having to burning up the algae. that's gotta' hurt the poor ol' dear... digesting algae. ;) i suggest fixing the fuel first and then see if she's still shaking! i LOVE my 1982 300SD turbo diesel mercedes-benz... obviously!!! mia in lakeland, FL

women with old cars, especially, have to know all about them!!! i am the proud owner of a 1982 300sd turbo diesel, too. had the same issue with black smoke. mechanic wanted $500. i fixed it with AFC-705 fuel additive from www.algae-x.net excessive black smoke when accelerating was caused by algae growing in the fuel tank. yes, algae can grow in diesel fuel, when the tank's so very old! the chemical additive cost less than 30$. exhaust is clean now, and she purrs like a kitten with over 300,000 miles on her, and gets 30 MPG. they're heavy engines... made of steel before 1985, not aluminum yet. the idol shake is probably just worn motor mount cushions. quick and easy to change. 'course, the shaking could just be from it having to burning up the algae. that's gotta' hurt the poor ol' dear... digesting algae. ;) i suggest fixing the fuel first and then see if she's still shaking! i LOVE my 1982 300SD turbo diesel mercedes-benz... obviously!!! mia in lakeland, FL

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