Does anyone know how to troubleshoot these EBCs?

It's doing this clicking as soon as the controller is powered up (listen):
https://vimeo.com/236314052

Turning the knobs on the controller changes the frequency of the clicking. Lower boost = higher frequency.

This started out of nowhere, after the car was sitting for a week.

I tested voltage between the wires to the solenoid and it appears to be a constant 6v to 11v, depending on the amount of boost dialed in. I only have a digital voltmeter so I'm not 100% sure it's constant voltage.

I couldn't hear if it does this at idle because the motor is too loud. So, I put a vacuum tester on the IN port of the solenoid and blocked the OUT. It holds vacuum when the controller is off. Once the controller is powered, the clicking starts and the vacuum bleeds off in pulses.
I could do a pressure test but assume it'll bleed just the same.

Any ideas? Is there a way to test if it's the solenoid or head unit that's fried?

It is probably not constant voltage. It will be a duty cycle like you experience when you put vacuum to it it bleeds in pulses. Your meter refresh rate is probably to slow to catch the pulse hence the 6v reading. If your meter can record min and max you will be able to see the 0v reading.

Thanks. I guess it works like a bleeder and when we go above wastegate pressure it starts to pulse? If that's how it works then I should expect 0v in vacuum. That means the head unit is faulty!

Just thinking out loud

I dont think it should be cycling as soon as it is powered on thought. What does the profec use to measure boost? I know Stock control was just calculated from MAF.

Maybe try a hard reset... disco the battery

It uses actual manifold pressure via hose to the head unit in the glove box.

Power is on the MPI circuit. Maybe I should try powering it directly to eliminate that circuit.

It sounds like it is seeing boost when powered up hence the cycling the solenoid. Does the display of profec show boost? Oh wait it doesnt have a display does it just like 3 knobs.

Nope just the knobs. Probably exploded the pressure sensor in the head unit