The turbocharger is used to increase the amount of air that enters the engine's cylinders. The increase of air allows a proportional increase of fuel that is injected into the cylinders. The results are:
| • | Increased power output |
| • | More complete combustion of the fuel |
| • | Cooling of the cylinder heads, the pistons, the valves, and the exhaust gas. This cooling effect helps extend engine life. |
Heat energy and pressures in the engine exhaust gas drives the turbine wheel. Exhaust gas is directed to the turbine housing. The turbine housing acts as a nozzle to direct the exhaust gas flow to the turbine wheel blades, which drive the shaft wheel assembly. The compressor wheel is attached directly to the shaft and rotates at the same speed as the turbine wheel. Clean air from the air cleaner and crankcase vapors are drawn into the compressor housing and wheel, where the air is compressed and delivered through a crossover pipe to the engine air intake manifold, then into the cylinders. The inside of the turbocharger compressor housing, the compressor wheel, and the inside of the intake manifold can be quite oily due to the ingestion of the crankcase vapors. A wastegate valve in the exhaust housing regulates the amount of air pressure rise and the air volume delivered to the engine from the compressor outlet.
The PCM monitors turbo boost pressure and controls the position of the wastegate valve. More vacuum is applied to the actuator to close the wastegate if increased boost is needed. The vacuum applied to the actuator is reduced if less turbo boost is needed. A reduction of vacuum allows the wastegate valve to open, resulting in additional exhaust bypassing the turbine wheel.
For more information about the vacuum operated wastegate controlled by the PCM, refer to Wastegate Actuator.
