Minimum viable vacuum at pump?

It only took a couple of seconds to nail 20". I just wish it was more like 30".

I cleaned out the pump and resealed it using some of that new wiz-bang anaerobic gasket material.

I will drive around in a few minutes with the gauge on the windshield to see if it deviates while driving. That is one thing I have not checked. I wish vacuum was a value on the VAGCOM plot screen....

OK. I drove around with my Mity-Mite laying on the windshield. The vacuum, measured off the pump, stayed pretty steady around 23". It dipped ~1" at the beginning of a shift or while braking.

It's almost impossible for an Air Conditioning vacuum pump to pull 30"

I have a vacuum gauge and turbo gauge for the ALH in my Vanagon. When I push on the accelerator, obviously the Turbo Boost goes up and at the same time, for a split second I can see the Vacuum gauge bleep ...... almost unnoticeable. Pushing down on the brake pedal moves the vacuum gauge a wee bit... two or three inches, then it bounces back where it was.

The one thing I just cannot confirm, why does the vacuum drop so quick when the engine is shut-down? You'd think there is a check valve inside the vacuum pump. I do have the same check valve in the maze of vacuum lines as was on the donor car.

Edit: Mine also hangs around 23 inches. But, elevation will affect vacuum.

That is helpful Andy. I think I am going to have a go a cleaning out my turbo. Not sure what else to do. Vacuum is fine, N75 is fine, my VAGCOM plots show frequent over-boost conditions.

There is a check valve but only between the N75 and the turbo actuator. My pump is driven off the cam and not the AC. But, I get your drift. 30" would be overkill as well.

I am at 7,500 feet which does affect my vacuum :-(

It would be difficult to draw 30" Hg of vacuum as the atmospheric pressure is only 29.92" Hg at sea level.
Maybe on a trip to Badwater?

Update: I finally ordered a new turbo actuator and my TDI runs like a banshee now!

I was able to monitor boost requested and actual boost. It looks like the original actuator was working but slowly. The controller would catch the overboost before the actuator could get it under control. I suspect it was "sticking" in the range of travel because it would eventually get the boost correct but not in time before the controller flagged the event.

For only US$40 I should have replaced it sooner.

flee said:

It would be difficult to draw 30" Hg of vacuum as the atmospheric pressure is only 29.92" Hg at sea level.
Maybe on a trip to Badwater?

Click to expand...

Vacuum is a negative amount, atmospheric pressure is positive.

wonneber said:

Vacuum is a negative amount, atmospheric pressure is positive.

Click to expand...

There is no such thing as negative ambient pressure. Zero is as low as it can be.
Vacuum is what gets subtracted from the ambient atmospheric pressure.
If the ambient air pressure is 29.92"Hg, then that is all there is to subtract from.

Faster said:

Update: I finally ordered a new turbo actuator and my TDI runs like a banshee now!
I was able to monitor boost requested and actual boost. It looks like the original actuator was working but slowly. The controller would catch the overboost before the actuator could get it under control. I suspect it was "sticking" in the range of travel because it would eventually get the boost correct but not in time before the controller flagged the event.
For only US$40 I should have replaced it sooner.

Click to expand...

I hope the $40 actuator isn't chinesium.
When I bought one from IDParts it was closer to $90.