2002 non egr isx 500 cm570 - turbo question

[AussieISX]

Yes there is no speed sensor in the turbo. The ECM calculates an overspeed through a boost reading from intake pressure. You either have a bad boost leak , the wastegate needs an adjustment, the diaphragm set up on the intake manifold where the wastegate hose gets line pressure is faulty and supplying to much pressure to the wastegate causing it to open prematurely. The hx60w on that engine will open The waste gate around 25 psi of line pressure and bleed boost off . So I doubt there's a problem with the diaphragm arrangement on the intake which is designed to reduce the line pressure to waste gate and allow it to open later and create more boost . It's most likely you have a bad boost leak somewhere to be only getting 18psi .