Circuit Description
Supercharger boost pressure is regulated under certain conditions to prevent engine and drive train damage. When the engine is operating under high boost conditions, the engine control module (ECM) can limit boost pressure to 83 kPa (12 psi) or less.
The ECM disables boost under the following conditions:
- Reverse gear is selected.
- Intercooler pump failure is detected.
- Electronic throttle control fault is detected.
- Excessive air temperature, pressure, or spark knock is detected
- Intake air temperature (IAT) sensor 2 is equal to or warmer than 120.5°C (248°F). Boost pressure is limited to 145 kPa (7 psi).
- Engine coolant temperature (ECT) is warmer than 125°C (257°F).
- Drivetrain abuse is detected.
- Vehicle speeds exceed 256 km/h (159 mph) in second, third or fourth gear for greater than 150 s.
The ECM controls boost pressure by limiting throttle control via logic in the software. At idle, engine vacuum is applied to the upper side of the bypass valve actuator, counteracting spring tension to hold the bypass valve open. When the engine load is increased, the engine vacuum is decreased, causing the spring in the bypass valve actuator to overcome the applied vacuum, closing the bypass valve and allowing the boost pressure to increase. The bypass valve starts to open when the vacuum is greater than 33.9 kPa (10 in Hg) and is fully closed when less than 11.9 kPa (3.5 in Hg). When reduced boost pressure is desired, the ECM enables boost protection by commanding the throttle, causing the supercharger inlet air pressure to drop relative to barometric pressure, allowing the bypass valve actuator to open the bypass valve, redirecting the charged air.