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Heavy-duty

Maintaining variable geometry turbochargers

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The use of variable geometry turbochargers (VGT) is now standard on heavy- and medium-duty truck engines. Older wastegate actuator turbochargers were generally controlled by pressure or vacuum and operated basically as an on/off device.

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Today’s heavy- and medium-duty engines incorporate electronically controlled VGT. These new advanced turbochargers provide improved response across wider operating ranges (engine speeds), improved engine performance, fuel economy and enhanced engine braking, and provide a quicker engine deceleration for quicker shifting than fixed geometry (older wastegate) turbochargers.

In addition, they allow for smaller engine displacements with increased horsepower and torque ratings, eliminating the need for older larger displacement engines in some applications.

The VGT actuator moves either vanes or a sliding sleeve inside the turbocharger which increases or decreases exhaust gases driving the turbine wheel, which in turn, increases or decreases turbo boost based on engine operating conditions.

These new VGTs are more complex than older wastegate turbochargers and technicians must be trained to accurately diagnose and repair them.

Mitchell 1 recommended the following turbocharger maintenance from its online Truck Series—a tool for techs to access the latest repair and diagnostic information to maintain, diagnose and repair these newer components.

Using the Cummins ISX15 as an example, some of the procedures for maintaining the turbocharger include:fig-1-cummins-x15

• Inspecting variable geometry actuator and mechanism for proper operation;
• Checking axial movement of turbocharger wheels and shaft;
• Checking radial movement of turbocharger wheels and shaft; and
• Calibrating turbocharger actuator to turbo charger.

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Regular service is always a crucial element in maintaining VGT performance within standards. Some maintenance items to keep in mind are:

• Regular engine oil changes;
• Regular coolant flushes;
• Inspecting for air leaks in the intake system;
• Inspecting for exhaust leaks; and
• Ensuring proper aftertreatment system function.

 

Additional truck repair and maintenance tips may be found in the Mitchell 1 ShopConnection Truck Blog.

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