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VAPC & Turboshaft coking...
Bruce,
Just to make sure we're all on the same page here... are you saying the variable absolute pressure controller (VAPC) up top side tends to coke up when the main turbocharger shaft cokes up, or that the wastgate itself cokes up? As you know, the oil line from the engine to the wastegate and on up to the controller (VAPC) is totally separate from the oil line that lubricates the turbo shaft.
We have a 1200 hour TSIO360(C) that's producing a little carbon and of course flecks get stuck in the wastgate inlet orifice, which will cause zero boost until enough oil pressure overcomes and forces stuff out of the way... but that orifice is pretty tiny and since unfiltered oil is taken off the bottom of the accessory case to drive the wastegate actuator, this can be a continuing headache as the engine ages. Carbon can also block the controller. It's a many 'splintered' thing!
SkyKing
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