Apparently there is a boost sensor, and a barometric sensor, as well as variable vane turbo.


Is there some good stuff I can read up on how this all works?

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Taken directly from the GM Dealerworld website:
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<TD align=middle width="50%">Document ID# 1394251
2004 GMC Truck GMC K Sierra - 4WD </TD>
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<H1>Turbocharger Description and Operation</H1>
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<TD align=middle>(1)</TD>
<TD align=left>Turbocharger Vane Position Sensor</TD></TR>
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<TD align=middle>(2)</TD>
<TD align=left>Turbocharger Vane Position Control Solenoid Valve</TD></TR>
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<TD align=middle>(3)</TD>
<TD align=left>Turbocharger Vane Position Unison Ring</TD></TR>
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<TD align=middle>(4)</TD>
<TD align=left>Turbine</TD></TR>
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<TD align=middle>(5)</TD>
<TD align=left>Turbocharger Vanes</TD></TR>
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<TD align=middle>(6)</TD>
<TD align=left>Hydraulic Piston</TD></TR>
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<TD align=middle>(7)</TD>
<TD align=left>Cam</TD></TR></T></TABLE>


The turbocharger increases engine power by pumping compressed air into the combustion chambers, allowing a greater quantity of fuel to combust at the optimal air/fuel ratio. In a conventional turbo, the turbine (4) spins as exhaust gas flows out of the engine and over the turbine blades. This spins the compressor wheel at the other end of the turbine shaft, pumping more air into the intake system.


The turbocharger for this system has vane position control by the engine control module (ECM). The vanes (5) can be opened and closed to vary the amount of boost pressure. Thus, the boost pressure can be controlled independent of engine speed. There are 9 controllable vanes in this turbocharger. The vanes mount to a unison ring (3) that can be rotated to change the vane angle. When the engine is not under load, the vanes are open to minimize boost and exhaust back pressure. To increase boost when the engine load requires it, the vanes are commanded closed. The ECM will vary the boost dependent upon the load requirements of the engine.


The turbocharger vanes are normally open when the engine is not under load. However, the ECM will often close the turbocharger vanes to create back pressure to drive exhaust gas through the exhaust gas recirculation (EGR) valve as required. At extreme cold temperatures, the ECM may close the vanes at low load conditions in order to accelerate engine coolant heating. The ECM may also close the turbocharger vanes under exhaust braking conditions.


The turbocharger control system utilizes the following components:<A name=ss1-1394251><A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1394251&amp;evc=sm&amp;pubid=437&amp;cellI d=133229&amp;mspsdsubkey=3243#ss1-1394251" target="_blank">
<H5>Turbocharger Vane Position Control Solenoid Valve</A></H5>


The vane position control solenoid valve (2) works in conjunction with oil pressure to control the turbocharger vanes. The solenoid valve uses 2 circuits; a control circuit and a low reference circuit. The engine control module (ECM) uses a pulse width modulation on the HI control circuit to control the solenoid valve. The ECM will control the solenoid valve to allow the engine o

Good stuff! Thanks !!


Mike