My ML 350 CDI 2009/2010 has a curious problem: black smoke when accelerating hard - sometimes.

I usually drive in the optimum torque range, between 1600 and 2200 RPM - no black smoke appears. But when you accelerate hard, a strong black smoke can be seen in the car's rearview mirror. However, when trying a second strong acceleration in sequence, there is no smoke. The black smoke will only return after a period without accelerating strongly again of about 100-200 km!

The PCV valve has already been replaced, EGR is clean, filters and oil are up to date, no errors appear in MBII or Star Diagnosys.

A slight increase in consumption and dificultty in speed increase are two other symptoms.

The car has 200.000 km, and it is with me since 80.000 km. Does anyone have any suggestions what it might be?

 

You are babying your car. You must exceed the 2,200 RPM and step into the passing gear (foot to the floor) multiple times and see if things get better.

 

Maj. Dundee, thank you so much for your reply.

But isn't black smoke a sign of rich mixture?

As there is no constant smoke, I suspect that there is an accumulation of oil somewhere, which with the strong acceleration is expelled.

I assume it's somewhere in the air piping from the PCV valve.

It can be in the resonator, in the intercooler or in the intake manifold. The question is where!

 

It's almost impossible to determine if it is black or grey smoke coming out of the exhaust by looking through the rear view mirror.

If you fear exceeding the kick-down RPMs, then seek professional help.

 

The black smoke is certainly a sign that your Diesel Particulate Filter (DPF) is not working or is missing. It’s essentially illegal for this to occur.

”Mixture” is not a term relevant to diesels. Instead of a constant fuel/air ratio (stoichiometric) like gasoline engines, the fuel/air mixture for a diesel is variable and this is how engine speed is increased/decreased. There is no throttle. Black smoke is simply unburned fuel … soot.

 

lkchris, thank your for your reply.

This car does not have DPF. - it is a version sold by Mercedes in Latin America. Euro Diesel was introduced only in 2012 - I live in Brazil.

Recently I changed the PCV valve bracket to solve the sucking oil problem. As you must know it is a very common problem that occurs in OM642 (but most of the people think that the sucking oil problem is the PCV valve and change it). The volume of oil sucking decrease a lot, but I think the intake manifold could be contaminated because I delayed a lot to make this repair.


Compare the hole diameter of the PCV valve bracket between the new and old part.