Boost Control System

BOOST PRESSURE CONTROL
^ The boost pressure control system consists of a wastegate valve and a wastegate actuator. The actuator, which is controlled by turbo boost pressure, controls the wastegate valve, which opens and closes the exhaust gas bypass passage.

^ The amount of turbocharger boost is limited to a maximum of 8.1 psi by the wastegate and actuator. Under normal to moderate loads, the wastegate valve is closed and intake air pressure changes in accordance with engine rpm and amount of exhaust gas. Under heavy loads, when intake air pressure reaches 8.1 psi, pressure acts on the diaphragm and overcomes actuator spring pressure, and the wastegate valve opens the bypass passage. As a result, flow of exhaust gas applied to the turbine wheel drops, turbine wheel rpm drops, and boost pressure decreases accordingly.

OVERBOOST PROTECTION
To prevent engine damage, fuel injection is cut off when intake manifold pressure reaches 11.0 psi (77 kPa), and calculated intake manifold pressure reaches a predetermined level. Calculated pressure is determined by the ECA from engine speed and amount of intake air.