A turbocharger is an exhaust-driven pump and compressor that increases air intake volume. It improves the volumetric efficiency of an engine. Because a turbocharger is driven by expanding exhaust gases, it is a free source of boost.
Expanding exhaust gases drive the turbine wheel. It's fastened to a shaft that spins the compressor wheel. The compressor wheel compresses the air-fuel charge in the intake manifold. This compressed charge is denser than the charge in a normally aspirated engine. A turbocharged engine's air-fuel charge is forced into the cylinders by the increased manifold boost pressure.
The Turbocharger Wastegate
The turbocharger boost pressure is regulated by a spring-loaded valve in the body or a wastegate and computer-controlled solenoid. When opened, the wastegate diverts some of the exhaust away from the turbine wheel, depriving it of exhaust pressure. Without this necessary reduction in output, excessive manifold and cylinder pressures would damage vital engine components. Once boost pressure is under control and reaches normal operating pressure, the wastegate closes.
Boost Pressure Problems
An underboost condition usually occurs when the wastegate stays open or opens too early. A sticking wastegate or wastegate linkage will also result in underboost. A restriction in the exhaust will reduce exhaust flow past the turbine wheel resulting in this condition. Underboost results in poor acceleration and a loss of horsepower.
The ECM controls an electric solenoid-operated vacuum valve that moves the wastegate diaphragm. A partially open or closed wastegate from a faulty valve, a disconnected vacuum line, or a leaking diaphragm will cause an overboost condition. Overboost can damage the turbocharger and the engine.
Turbocharger Bearing Failure
Premature failure is typically due to a lack of maintenance or contaminated and unchanged oil, resulting in bearing damage. Turbocharger bearings spin at very high speeds; they quickly overheat if not lubricated sufficiently. Worn and faulty bearings rapidly lead to damaged seals and blue-gray exhaust.
Turbocharged engines are port injected and have a lower compression ratio than standard engines. The parts are usually not interchangeable. The engine's cooling system keeps a liquid-cooled turbocharger cool. The cooling system lines to the charger must be maintained and functioning correctly. Check the air tube for obstructions and that the air filter is clean. Dirt passing the air filter can damage the compressor blades.