Turbocharger Overview:

Overview of exhaust and intake air flow through turbocharger. Click image for higher resolution (~90K).

Turbocharger Control System

RPM	0 to 3,000		3,000 to 4,500		4,500 to redline
	Light Load ------------------------------------------------------------------------------>> Heavy Load
Primary Turbo	Boost
Secondary Turbo	Stop		Preliminary Rotation		Boost
Turbo Pre-Control	Duty Control				Duty 5% (fully open)
Wastegate Control	Duty 95% (fully closed)				Duty Control
Charge Releif	OFF (vent to air cleaner)				ON
Charge Control	ON (isolate Primary and Secondary Compressors)				OFF
Turbo Control	OFF				ON

0 to 3,000 RPM

• In this RPM range, boost is produced by the Primary Turbocharger only. At this time, most of the the exhaust is directed to the Primary Turbo by the Turbo Control, and the Secondary Compressor is isolated from the Primary by the Charge Control. Boost pressure is mostly regulated by the Turbo Pre-Control.

3,000 to 4,500 RPM

• In this RPM range the Turbo Pre-Control valve is almost fully opened and preliminary rotation of the Secondary Turbo has begun, any boost pressure from the Secondary Turbo is vented via the Charge Releif Valve to the air cleaner. Boost pressure is regulated by the Turbo Pre-Control and the Wastegate Control.

At 4,500 RPM

• At this time, the Secondary Turbo is at full preliminary rotation speed, the Turbo Control is opening, Charge Releif closes causing the Secondary Turbo to surge for a short time. The Charge Control then allows Secondary boost to be added to the Primary boost.

4,500 to Redline

• The Turbo Control is fully opened, and boost pressure is created by the Primary and Secondary Turbochargers. When both Turbochargers are actuated, boost prerssure regulation is preformed by the Wastegate Control.

From the above description, there is not much happening when only the Primary Turbocharger is operating. However, at 4,500 RPM when the change over occurs, lots of solenoids and actuators are changing operation. This is when most of the problems occur.