Supercharger and Intercooler Systems
Supercharger Bypass System
The Supercharger Bypass (SCB) System (Figure 137) allows the high pressure air at the outlet of the supercharger to vent back in the inlet of the supercharger, equalizing the pressure. This eliminates the boost (increased pressure that a supercharger produces) for times when supercharger function is undesirable. The components in this system are the vacuum bypass actuator (Figure 141) (which controls the bypass valve inside the supercharger), a supercharger (boost) bypass (SCB) solenoid (Figure 138) and a vacuum reservoir (Figure 139). The system normally operates with engine vacuum applied to the upper port of the vacuum bypass actuator, while the lower port references the air pressure in the clean air tube to cancel out any pressure difference in the intake air system. The actuator is set to open (bypassing the supercharger) during high vacuum engine conditions. As the throttle is opened, and engine vacuum decreases, the actuator closes to allow the supercharger to pressurize the air in the manifold. If an undesirable condition occurs in the engine, such as overheating or a critical Electric Engine Control (Electronic EC) sensor failure, the powertrain control module (PCM) also has the ability to control the SCB solenoid and direct the vacuum bypass actuator to bypass the supercharger. Once the engine condition has been corrected, the PCM allows the engine vacuum to control the vacuum bypass actuator.
Supercharger Assembly
The supercharger assembly (Figure 136) is a positive displacement pump. Its purpose is to supply an excess volume of intake air to the engine by increasing air pressure and density in the intake manifold. The supercharger assembly incorporates the bypass system to reduce air handling losses when boost is not required, resulting in better fuel economy. When integrated on the engine, the supercharger will increase torque across the entire engine operating range from 25 to 50 percent without compromising driveability or emissions. The supercharger is matched to the engine by its displacement and belt ratio, and can provide excess airflow at any engine speed. It contains two three-lobed rotors. The helical shape and specialized porting provide a smooth discharge flow and low level of noise during operation. The rotors are supported by ball bearings in front and needle bearings at the rear. The drive gears are pressed into place, therefore the supercharger is replaced as a unit, and is not serviceable.
Supercharger (Boost) Bypass Solenoid/(Thermactor Air Control Solenoid/Vacuum Valve Assembly)
The supercharger (boost) (SCB) solenoid (Figure 138) is used to control intake manifold vacuum to the vacuum bypass actuator. This part is replaced in field service diagnostics under the part name of a thermactor air control solenoid/vacuum valve assembly (part number 9H465). The PCM transmits an output signal to the SCB solenoid, thereby activating the solenoid to apply stored vacuum from the reservoir to the actuator, when an undesirable condition occurs in the engine. Once the engine condition has been corrected, the solenoid will be de-activated by the PCM, allowing engine intake manifold vacuum to control the actuator. The SCB solenoid is normally de-energized.
Vacuum Reservoir Assembly
The vacuum reservoir assembly (Figure 139) stores vacuum that is applied to the vacuum actuator when a condition such as overheating or a critical sensor failure is generated. This allows the vacuum actuator to bypass the supercharger.