Hello , I've a Volvo 940 1995 with a b200ft engine. Recently I've noticed that black smoke comes from exhaust & a very poor mileage about 9 miles per gallon, engine rough at idle but clears up on acceleration and lambda light on . is this comes form a bad injectors , mass air flow or what? please help Thanks,

just about everyone does with either an old car or a new car with high mileage.how excessive? is oil consumption.well first thing is to check for oil leaks either underneath the motor or any oil lines feed into the motor .any major leaks would be pretty noticeable.if none are present then one would assume that your motor is burning the oil through the exhaust system .check to see what color smoke is coming threw the tail pipe.blue or black smoke indicates oil burning white will indicate engine coolant burning.in any case some color smoke is normal just depends on how much.so lets say your exhaust smoke is normal still could be burning oil just not a noticeable amount.on average you shouldnt have to add anymore than 2 quarts a month or every 1000 miles .depending on your driving conditions if you are having to add more than this there would be a leak some where or heavy color smoke.keep up on oil changes and always add lucas oil usually 1 quart its alot thicker than conventional oil so it reduces engine wear and will handle any small leaks in the engine components like the pistons and rings.if problem still present get to a dealer or certified mechanic as soon as possible good luck.

worn out piston rings require replacement..

Hi there:Black smoke is caused by excess fuel that has entered the cylinder area and cannot be burned completely. Another term for excess fuel is "running rich." Poor fuel mileage is also a common complaint when black smoke comes out of the tailpipe. Black smoke out the tailpipe is the least cause for alarm. Excess fuel will usually effect engine performance, reduce fuel economy, and produce a fuel odor.
How did the fuel get into the cylinder in the first place? Some of the causes of excess fuel are a carburetor that is out of adjustment, a faulty fuel pump, a leaky fuel injector, or a faulty engine computer or computer sensor. If black smoke is present, check the engine oil as in the white smoke example to make sure excess fuel has not contaminated it. Do not start the engine if a heavy, raw fuel smell can be detected in the engine oil. Call your mechanic and advise him of what you have found.
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Yes

Check the fuel pressure regulator, it may have gone bad and running the engine rich. Good luck

Black smoke is caused by excess fuel that has entered the cylinder area and cannot be burned completely. Poor fuel mileage is also a common complaint when black smoke comes out of the tailpipe. Black smoke out the tailpipe is the least cause for alarm. Excess fuel will usually effect engine performance, reduce fuel economy, and produce a fuel odor. Some of the causes of excess fuel are a carburetor that is out of adjustment, a faulty fuel pump, a leaky fuel injector, or a faulty engine computer or computer sensor. If black smoke is present, check the engine oil to make sure excess fuel has not contaminated it. Do not start the engine if a heavy, raw fuel smell can be detected in the engine oil.

Black smoke is caused by excess fuel that has entered the cylinder area and cannot be burned completely. Poor fuel mileage is also a common complaint when black smoke comes out of the tailpipe. Black smoke out the tailpipe is the least cause for alarm. Excess fuel will usually effect engine performance, reduce fuel economy, and produce a fuel odor. Some of the causes of excess fuel are a carburetor that is out of adjustment, a faulty fuel pump, a leaky fuel injector, or a faulty engine computer or computer sensor. If black smoke is present, check the engine oil to make sure excess fuel has not contaminated it. Do not start the engine if a heavy, raw fuel smell can be detected in the engine oil.

you put 2 many oil in the engine

black smoke( too much gas)
blue smoke( burning too much oil)
white smoke( burning coolant)

hello,according to service information;smoke formation or si 07.16-p-0004a (service inform) from mb ,your engine have normal function,if you want ,ask your dealer about the service inform with number 07.16-p-0004a,you can read the explanation regarding your problem,ty