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Fluctuating Manifold Pressure

davej11

Member
I recently finished installing a G3X with GEA24 and Garmin sensors and have been experiencing manifold pressure fluctuations. At WOT it is solid and at pressures under 20" it is solid, but between 20" and 25" it can move up and done rather quickly as much as 3-4" without touching anything. I've looked for plumbing leaks and wiring issues but so far nothing. I saw an old thread about putting a restrictor in the line, but am reluctant to do that without further research. Does anyone have ideas?
 
Possibly a bad MAPsensor but before changing it, try restricting the hose going to the manifold to stem some of the pulsation.
 
I added a restrictor from McMaster Carr, P/N 3820K12 for my manifold pressure line. It is a 1/8 NPT and has a .008 opening. It works perfectly on my G3X system and gives me rock steady manifold pressure.
 
You are taking pressure readings at a point VERY close to an intake valve, not in a plenum like on you car. This can introduce reverse flow coditions and cause oscillations. For many, a restrictor will be required in the line to stabilize readings. On my 6, I tapped the MAP line into the servo and is rock steady without a restrictor. On the 10, I used the #5 cylinder and it required a restrictor to smooth out the readings. It creates a lag condition, but only a second or two.

Larry
 
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I recently finished installing a G3X with GEA24 and Garmin sensors and have been experiencing manifold pressure fluctuations. At WOT it is solid and at pressures under 20" it is solid, but between 20" and 25" it can move up and done rather quickly as much as 3-4" without touching anything. I've looked for plumbing leaks and wiring issues but so far nothing. I saw an old thread about putting a restrictor in the line, but am reluctant to do that without further research. Does anyone have ideas?
The G3X Installation Manual explains that you might need to install a restrictor between the sensor and the engine pickoff.

Snubber.png

Steve
 
A typical restrictor fitting in cylinder 3, or 4, or 5 or 6 (for 6 cylinder Lycomings) can be used with a standard -4 hose. Restrictor orifice usually +- .040 generally works well. In some cases, we use a -3 hose assembly with a fitting stem ID of .079. Most have been used without a restrictor fitting, even with PMags or SureFlys without adverse affects or pressure pulses.

WE do have some restrictors, and can make them in straight, 45* or 90* versions for your custom creations.

Tom
 
I installed a snubber (this one, PS-8G fitting from Omega Engineering) recently and it cured the problem completely.
 
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Don’t forget to add removing and cleaning the restrictor to your annual checklist. After 15-18 months of flying I found the manifold pressure to “stick” and not move as much. Cleaned the restrictor and solved the issue. It was visibly blocked.

E
 
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