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Grounded - fluctuating manifold pressure in flight

samgaddis

Member
Hi all, I have an -14A with the YIO 390, and the other day I noticed the manifold pressure fluctuating from 19-26 without pilot input. I was aiming for 23" MAP and 2300 RPM, but could not get the engine to stabilize there as it normally would. The engine at the time was leaned as I always do.

Some other considerations:
- The airplane is normally hangared but was outside the prior night. I pulled the cowling and saw no obvious loose hose clamps or damaged wires / lines.
- Mag 2 is showing a 250 RPM drop while Mag 1 is showing 50
- I have not checked to see if I have SB'd Kavlico sensor, but I will soon

Here's a normal flight profile (from the previous day)

Here's the flight where I first noticed the manifold pressure issue.

And here's a ground run-up test I did the following day showing a similar fluctuating MP.

I am having a hard time finding a mechanic who is available so any guidance is appreciated.
 
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Thoughts:

1. Has the Kavlico sensor SB been completed (if so should be in the logbooks)?

(https://www.vansaircraft.com/service-information-and-revisions/sb-00006/)

Not sure this would affect the reading but it's a consideration

2. Have you checked all MP lines/connections for leaks? If you know how to remove the cowling, the standard location for MP sensor and lines is passenger side upper firewall. Main line connects the sensor to engine block, and there may be additional "t" connection(s) to ignition system if you have electronic ignition. Not too hard to do a visual inspection and look at lines/connections if you're comfortable pulling the upper cowling.
 
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I had a similar issue about 10 hours into my Phase I. It turned out to be a loose connection of the MP hose at the MP pickup point just behind cylinder #3. Check all the connections from the MP pickup point to the MP sensor. If you have EI with MP sensing you will need to check those connections as well.
 
What does Savvy Aviation have to say about the issue? And where are you reading MP on your graphs?
 
MP Fluctation

Hi all, I have an -14A with the YIO 390, and the other day I noticed the manifold pressure fluctuating from 19-26 without pilot input. I was aiming for 23" MAP and 2300 RPM, but could not get the engine to stabilize there as it normally would. The engine at the time was leaned as I always do.

The airplane is normally hangared but was outside the prior night. I pulled the cowling and saw no obvious loose hose clamps or damaged wires / lines.

Here's a normal flight profile (from the previous day)

Here's the flight where I first noticed the manifold pressure issue.

And here's a ground run-up test I did the following day showing a similar fluctuating MP.

I have spoken with 3 mechanics and have one I'm hoping can look at it soon as I've got a bunch of IFR training scheduled in two weeks. But I'm wondering if you fine folks might have any leads as well?

Do you have a snubber fitting installed between the hose and the sensor? These are typically installed to dampen manifold pressure fluctuations. An example we provide in our installation materials is the Omega PS-8G fitting.

Thanks,

Justin
 
- Sometimes condensate (water, fuel, or carbon) can contaminate a MAP sensor. Insure sensor is mounted in a position that does not allow anything to migrate 'down' the hose & collect in the sensor.

- Check all wiring connections, at the sensor & at the monitor.
 
What does Savvy Aviation have to say about the issue? And where are you reading MP on your graphs?

They said: "With FF stable on this flight, this is either a bad connection or probe but might also be an intermittent leak in the MAP line. MAP sensors don't fail often so we'd suspect the wiring or a leak."
 
They said: "With FF stable on this flight, this is either a bad connection or probe but might also be an intermittent leak in the MAP line. MAP sensors don't fail often so we'd suspect the wiring or a leak."

In case this is helpful:

The MP sensor IIRC has 3 wires that connect to wires coming through the firewall. Should be easy to locate and inspect the connections at the sensor. Depending on your avionics, the wires coming through the firewall usually go to a separate box (on the cabin side of firewall) with wires for all the other monitoring functions (CHT, EGT, etc). With most Garmin packages this is the GEA 24 - the wires would terminate in one of the dsub connectors that plug into this box.

For Dynon the equivalent box is the SV-EMS-220 or similar (I'm much less familiar with Dynon boxes but that's what I understand from their web page). Also has dsub connectors.

Garmin: https://www.garmin.com/en-US/p/107443

Dynon: https://dynonavionics.com/engine-monitoring-modules.php
 
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