What boost do they make stock? If the solenoid is stuck open on the EBC you should still be able to get wastegate pressure & it should not be laggy really. Plug your old solenoid in and see what happens? If it was a torn diaphragm you would make silly amounts of boost. Do you have an inline filter in the EBC hosing

Can you try to move the actuator by hand (using tools / air line) at all, to see what happens

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Cheers,

Simon.