Low vacuum pressure indication but instruments all work?

[kajo]

Dear Mooney owners!

Hope you can share some light on my issues. I have a 2001 Mooney Ovation with 2100 hours. It has steam gauge. I replaced the vacuum pump 2 years 200 hour ago, when after landing with my CFI the AI tumbled completely in matter of seconds.  A few weeks ago I was noticing during flight the vacuum pressure indicates low like 4.0inHg gradually dropping to 3.5inHg after 2 hours of flight. My mechanic did various things like cleaning filter, tighten regulator which helped increase the pressure by like 0.3inHg. Now a few hours of flight later, it drops again now the vacuum gauge is constantly reading 3.0inHg (I suppose this is the lowest the gauge can go?)  However my AI, HI, and autopilot all works perfectly fine (in VFR condition I am flying).  I just wonder, is my next step replace the vacuum pump or what?  What would be the lowest possible cost including install labor to get rid of vacuum?  I just got a quote for Aspen E5, $16000 including install labor.  Very expensive! 

[Niko182]

11 minutes ago, kajo said:

Dear Mooney owners!

Hope you can share some light on my issues. I have a 2001 Mooney Ovation with 2100 hours. It has steam gauge. I replaced the vacuum pump 2 years 200 hour ago, when after landing with my CFI the AI tumbled completely in matter of seconds.  A few weeks ago I was noticing during flight the vacuum pressure indicates low like 4.0inHg gradually dropping to 3.5inHg after 2 hours of flight. My mechanic did various things like cleaning filter, tighten regulator which helped increase the pressure by like 0.3inHg. Now a few hours of flight later, it drops again now the vacuum gauge is constantly reading 3.0inHg (I suppose this is the lowest the gauge can go?)  However my AI, HI, and autopilot all works perfectly fine (in VFR condition I am flying).  I just wonder, is my next step replace the vacuum pump or what?  What would be the lowest possible cost including install labor to get rid of vacuum?  I just got a quote for Aspen E5, $16000 including install labor.  Very expensive! 

Since its a 2001you probably have the moritz gauges. Id probably start with that. Try turning on the standby pump and see if the pressure changes. Aspen install also seems tad bit expensive. Id check some more quotes out.

[David Lloyd]

E5 Lists for $4995 plus options, $16k does seem expensive for an install.  

[N201MKTurbo]

I would put a test gauge on it to verify your ships vagus is accurate.

wow, interesting spell check correction.

[Guest]

Either a vacuum sensor failure or the hose to the sensor.

Clarence

[kajo]

Yes I have the Moritz gauge. If the hose to the sensor fails (do you mean leaks?) will that cause the vacuum pressure to drop, same as a less wind blowing the Gyro?  Is AI/HI/AP supposed to work perfectly if vacuum pressure was actually 3.0inHg? 

Below is the quote. Apparently for AP there is another item EA100. 

 

[carusoam]

The vac pump generates a pressure differential...

That differential generates a wind...

That wind blows across the instrument’s vanes...

Those vanes spin the gyro...

 

If the wind isn’t strong enough... the gyro won’t spin fast enough... 

If the gyro doesn’t spin fast enough... it will misbehave...

 

The vac gauge is usually calibrated with a green arc...too low, is too slow...

 

What cause low vacuum...

• pump fault...
• air leak.
• blocked filters or lines...
• contaminated vac line...

 

known long body vacuum challenges...

Go to the battery access panel on the pilot side...

Find the BU vac pump...

Look for clear PVC hose...

If you have a clear PVC hose... this could be a source of contamination in your vac system... see if there is any oily substance  in the clear vac hose...

PP thoughts only, not a mechanic... 

Best regards,

-a-

[Guest]

6 hours ago, kajo said:

Yes I have the Moritz gauge. If the hose to the sensor fails (do you mean leaks?) will that cause the vacuum pressure to drop, same as a less wind blowing the Gyro?  Is AI/HI/AP supposed to work perfectly if vacuum pressure was actually 3.0inHg? 

Below is the quote. Apparently for AP there is another item EA100. 

 

The fact that the instruments seem to be working fine, it suggests sensor failure or a leak in the hose to the sensor.  I’ve seen this before in a Bravo when a non approved hose failed.

Clarence

[carusoam]

Wait a sec...

Tumbling gyros after landing doesn’t Sound like the gyros are working properly...

But, the Doc’s advice is still valid...

Best regards,

-a-

[Guest]

I don’t think I misread the post?

“However my AI, HI, and autopilot all works perfectly fine (in VFR condition I am flying).  “

Clarence

[kajo]

>"Tumbling gyros after landing doesn’t Sound like the gyros are working properly..."

That was 2 years ago before I changed the vacuum, my point is that the gyro does not fail gradually with low vacuum pressure in my experience but they fail in seconds when engine rpm is reduced. 

>I don’t think I misread the post? “However my AI, HI, and autopilot all works perfectly fine (in VFR condition I am flying).  “

You did not, the Autopilot works perfectly to fly the airplane in perfect straight line despite turbulence and cross wind. I actually flew in this state (3.0inHg and low vac warning light flashing) in some IFR as well as VFR without problem, but am scared if this eventually leads to AI/AP failure while in IMC. 

 

[cbarry]

I’m not an AP mechanic, but this issue sounds a lot a dry rotted/leaky hose/line going to the vacuum gauge—similar to as M20Doc has suggested.  

[carusoam]

Oops, my bad...

I mis-read posts all the time...

I’m getting Better slooooowly...  

My apologies!

Best regards,

-a-

[Guest]

8 hours ago, carusoam said:

Oops, my bad...

I mis-read posts all the time...

I’m getting Better slooooowly...  

My apologies!

Best regards,

-a-

You’re not alone, I have to re-read many post to make sure I understand the issue.  You get far more of them right than wrong.

Clarence