Theory Of Operation

GENERAL OPERATION:  The Powertrain Control Module (PCM) monitors feedback from the Boost Pressure Sensor to manage the Turbocharger system boost pressure. The main objective of the PCM is to prevent an over boost condition since this can cause damage to the Turbocharger or engine assembly. The PCM compares the Boost Pressure Sensor actual  reading to the desired  boost pressure to determine if an under boost or over boost condition is present. Anything that affects exhaust flow or intake air flow through the Turbocharger can cause an under boost or over boost condition. This can include leaks or blockages in the intake air system plumbing or exhaust system. These systems should be carefully inspected before condemning any components.

The two main components used to manage boost pressure are the Wastegate and Turbocharger Surge Valve.

• The base Turbocharger boost pressure is managed by the Wastegate  . The primary function of the Wastegate is to regulate the maximum  boost pressure in a Turbocharged engine.
• The Turbocharger Surge Valve  is used to vent the boost pressure trapped between the Turbocharger and Throttle Body when the throttle plate is closed suddenly. The Turbocharger Surge Valve is de-energized and spring loaded closed during normal engine operation. The PCM energizes the Turbocharger Surge Valve to overcome the spring pressure and open the valve. When the Surge Valve is opened the boost pressure trapped between the Turbocharger and the Throttle Body is vented back to the inlet of the Turbocharger, relieving the pressure and preventing compressor surge.