So, in case you're not confused enough already, here's my explanation:

The wastegate is set up to provide 5.0+/-.4 psi boost. This is the factory setting, but it's adjustable by turning the pushrod on the wastegate. The wastegate responds to the output pressure of the compressor to maintain this boost level: there's a boost pressure feedback line that runs from the compressor, through the APC solenoid, and to the wastegate.

The APC solenoid, however, can open and allow this control pressure to bleed back to the compressor inlet, effectively porting the control pressure away from the wastegate. This mode allows the wastegate to close and raise the boost pressure.

Switching between these modes (sometimes very quickly) is how the APC system modulates the boost pressure.

When the APC solenoid is closed, due either to a failure or to APC system modulation, the most you can get is 'base' boost. Changing your base boost only regulates the low-end of your APC system regulation. It doesn't affect the maximum boost your turbocharger is able to generate (however it will affect the dynamic condition where the APC system is modulating the solenoid to provide intermediate boost levels).

The APC solenoid get its power from the APC control module; the module opens the solenoid by providing 12VDC, allowing the boost to go above 'base'. On cars with Cruise Control the ground side of the APC solenoid is routed through a vacuum switch that opens the circuit when Cruise is enabled, defeating the APC solenoid and limiting the car to 'base' boost.

posted by 130.76.3...

• Turbo Wastegate, Joe M., Wed, 27 Oct 2004 11:38:41
  • Re: Turbo Wastegate, Bill S., Wed, 27 Oct 2004 14:30:19 <-- Viewing This Message
    • How high will the needle go in base boost only mode?, tsw, Thu, 28 Oct 2004 11:34:36
      • 1/3 or so into the yellow n/m, RS , Thu, 28 Oct 2004 12:41:06
    • Damn good info BillS! n\m, lms, Wed, 27 Oct 2004 15:03:17
  • Wastegate triggered by APC, Ken , Wed, 27 Oct 2004 12:29:11
    • Not true, Steve Schwedland , Thu, 28 Oct 2004 10:30:19
      • Not true?, Ken , Thu, 28 Oct 2004 11:48:37
        • The wastegate works independently of the APC, Steve Schwedland , Thu, 28 Oct 2004 15:02:32
          • Now I'm even more confused!!, Ken , Fri, 29 Oct 2004 12:30:44
            • Re: Now I'm even more confused!!, Steve Schwedland , Fri, 29 Oct 2004 12:50:49
  • Re: Turbo Wastegate, lms, Wed, 27 Oct 2004 12:10:44
    • Re: Turbo Wastegate, Joe M., Thu, 28 Oct 2004 07:27:51

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