Should the top of a wastegate hold vacuum?

[gsxrken]

My Mityvac hand pump won’t hold a vacuum or- switched the other way- maintain pressure when attached directly to the wastegate. I ASSume this means the rubber diaphragm inside is shot? But I figured I post here in case they’re not that hermetically sealed off, and the much higher vacuum or pressure signals from a running engine will overcome it?

[Mixed76]

It should hold vacuum or pressure.

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[gsxrken]

I’m not convinced yet. Could the lower port that is fed from the intercooler leak out around the valve stem? I understand those are a loose fit to start and get worse over time.
I guess I could see if it is holding vacuum and pressure from the top vent to atmosphere, no? That should be isolated from the valve guide. Have to get back under there and see if that’s doable without removing the WG from the exhaust.
Helluva a way to spend $185 for a rubber diaphragm if that’s what it comes to:
https://www.pelicanparts.com/More_Info/93012321001.htm?pn=930-123-210-01-M127

[gsxrken]

Ok too much Sunday morning coffee and going off half-cocked... check.
For the sake of future searchers:

YES, the diaphragm should hold vacuum or pressure IF you check at the top of the WG, where the vent to open air is. I was able to check at the end of metal hose vent pipe without taking anything apart, and it held. Thankfully.

I then took my air compressor and regulated it way down to 15psi and applied pressure to the lower port like in my first picture. Nothing. Then I increased air pressure to about 18PSI and I heard the “thunk”of the wastegate valve opening. By depressing and releasing my rubber tipped air blower nozzle, I could hear a thunk/thunk as it opened and closed.

So my WG is fine. Still need to figure out why my car can sneak up to 6000rpm but hiccups when boosting to it. I thought maybe my overboost was kicking in.

[donbecker1234]

Ken,

Check out page two of this thread, has a link to the test procedure for Tial, should be the same:

Wastegate Advice: stock rebuild or Tial? Or?

[Mixed76]

Glad you sorted it, I started to try explaining top and bottom but got irritated with typing on the phone.

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[mark houghton]

Originally Posted by gsxrken

I then took my air compressor and regulated it way down to 15psi and applied pressure to the lower port like in my first picture. Nothing. Then I increased air pressure to about 18PSI and I heard the “thunk”of the wastegate valve opening.

Yep, that's been my experience too. One would logically think that the air pressure needed to actuate the valve would be whatever PSI (or bar) pressure rating the WG spring has....but not so. Although it's been years since I've done this test, if I recall needed somewhere around 15-18 PSI to trip my WG with a .8 BAR spring.

When bench testing, it has to do with air pressure leaking past the valve stem. On the car, you have exhaust back pressure working against that leakage.