Wastegate Valves

Vacuum operated, solenoid controlled, wastegate actuators are used to open and close the normally open wastegate valves. A spiral spring in the actuator housing works in the opening direction while vacuum in the diaphragm housing works in the closing direction. The engine control module (ECM) supplies a signal to the solenoid valve which regulates vacuum to the actuator. When the vacuum overcomes the spring force, the actuator rod moves, closing the wastegate valve to a corresponding degree. The ECM changes wastegate valve position by varying the signal to regulate turbine speed.

At low loads, (less than barometric pressure), the valves are open, allowing exhaust gas to bypass the turbines and reduce fuel consumption. When a request for boost pressure is received, the valves close and the pressure increases. As the boost pressure (and air flow) increase towards the desired level, the wastegate valves are gradually opened to maintain boost for the current operating condition. The force balance between this pressure and the turbine pressure on the wastegate valve itself regulates the amount of exhaust gas that flows through the turbine and the wastegate channel. Controlling the flow through the turbine regulates the power delivered to the compressor to vary the boost pressure.

When certain DTC's are set the system is limited to base boost (also known as mechanical boost). This is the boost pressure the system will create with the wastegates fully open. When a DTC is set, the solenoids feed little to no vacuum to the wastegates, allowing them to reach their full (or nearly full) open positions. This limits the boost pressure by allowing as much flow as possible to pass through the wastegate valve, this boost pressure is very close to atmospheric pressure under almost all driving conditions. Any condition or DTC that causes the intake or exhaust cams to be parked will also limit the system to base (or near base) boost.