( copied and pasted from my other thread)
Well, I think I've muddled through the issue in my head. I haven't been able to check anything out, as I'm not at my car right now, but! first gen EVCs do not have external switches for internal or external wastegates. They are sold as either or from HKS back in the day. However, they do have the switches inside the control unit to change it from internal to external or vice versa.
So, on a external gated setup, the diaphragm side of the wastegate is fed with constant pressure from the charge pipes. Then, your boost controller feeds the spring side of the wastegate with pressure. So the boost from the boost controller actually helps "increase" spring pressure. So spring pressure with a boost controller would be the boost controller sealed shut.
On an internally gated setup, boost from the charge pipes is feeding the diaphragm side of the wastegate. Very simple... Spring pressure with a boost controller would be the boost controller wide open.
So in my (hopefully) case, with the EVC set to an external gate setup, when I first noticed that the boost was over 10 psi, I switched it over to manual, and turned the volume knob all the way down, which would basically result in stock boost... Since the EVC is setup for external gates, then it would seal the valve shut. Which would be correct in an externally gated setup. This resulted in my completely uncontrolled boost. Then, I switched the control units power off, which also results in stock boost. Again, since it is set up for external gates, it sealed the valve shut, resulting in complete loss of boost control.
Also, the reason it didn't control boost on the low setting, is because the way it controls boost for internal or external gates is completely different. For one psi over spring pressure in a external gate, the boost controller has to feed the spring side with 1 psi of boost (it's probably a hair bit over that since the spring would take up some surface area on the diaphragm.). In order to raise the boost pressure one psi the boost controller needs to feed the diaphragm side with spring pressure once the manifold reaches spring pressure, plus one psi.
So yes, EVENTUALLY the pressures would equal out.. Maybe if I switched it over to the high side, then it would hold 15 psi or something like that... But I think I'll just move the dipswitches around...