Supercharger: Testing and Inspection
Boost Control System Diagnosis
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 powertrain control module (PCM) can limit boost pressure to 83 kPa (12 psi) or less. The PCM disables boost under the following conditions:
* When reverse gear is selected
* When the vehicle is decelerating
* If an intercooler pump failure is detected
* If the intake air temperature (IAT) sensor 2 becomes excessively high
* If the engine coolant temperature (ECT) becomes excessively high
* Under heavy load in first and second gear at engine speeds above 5,800 RPM
* When drivetrain abuse is detected
The PCM controls boost pressure by using the boost control solenoid. The boost control solenoid is a normally open valve. Under most conditions, the PCM commands the boost control solenoid to operate at a 99-100 percent duty cycle. This keeps the solenoid valve closed and allows only inlet vacuum from the supercharger plenum to the bypass valve actuator to control the position of the bypass valve. 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 to overcome the diminishing applied vacuum, closing the bypass valve and allowing the boost pressure to increase. When reduced boost pressure is desired, the PCM commands the boost control solenoid to operate at a 0-98 percent duty cycle. This opens the solenoid valve and allows boost pressure to enter the bypass valve actuator at the lower side to counteract the spring tension, opening the bypass valve, and recirculating excess boost pressure back into the supercharger inlet.
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