You should start inspection identify with visual problems. They may be well identified by yourself.
The color of the exhaust gas. If you saw that the exhaust gas has a black color, it indicates a blocked valve and a leak in the reservoir. To resolve this failure, you must check the connection of the pipes and to inspect the air filter.
Also it is worth a close look at exhaust color. White and bluish tint gas talks about the oil gets into the exhaust system. This happens in case of failure of the engine or turbine.
Oil consumption is increased. Start standing the search for damage with inspection of the air filter. Next, go to the inspection of fixtures and checking the pressure in the housing. Viewing the axis backlash it is possible to determine the wear of the turbine. If these items are in good condition, the cause of the fault is in the drain oil line.
There are other causes of damage of the turbine, which require a thorough and professional examination.