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Manifold Pressure Fluctuations

Mongoose

Member
I?m getting Manifold Pressure Fluctuations with my IO-390 and G3X. I?ve replaced my sensor and it is better but still don?t have rock solid pressure. I also have one P-MAG with its normal rubber hose attached. I?ve seen a note somewhere that a restrictor fitting might help. Anyone have any specifics on what I?d need? Do others have this issue? I?ve checked for leaks and all seems good.
 
I was seeing pulsing on the G3X at 2400 RPM.

Garmin recommends the Omega Engineering PS-8G snubber. I installed it immediately in front of the Kavlico MAP transducer into the 3 port manifold.

B
 
I also used the Omega Engineering PS-8G snubber on the manifold pressure line. It is needed to get a stable reading. The G3X manual did not say where to install it in the line. It may seem convenient to screw it into the port of the cylinder head. I did that and found out after about a year that it was a mistake. The snubber became almost totally blocked with carbon. Then I was seeing manifold pressure above atmospheric with the engine shut off and crazy readings with it running. So, install it at the transducer so that it is remote from the engine.
 
...and in the for what it's worth category, my old RV-7 with Rob's brand-new-at-the-time AF-3400EM, did not have any sensitivity issues with MAP.

Of course, he used Delphi or Delco MAP sender unit; probably not nearly as sensitive to the pulses as the Kavlico.

B
 
Pretty sure a little bushing in your line , clamped in place so it doesn't move and a .040" hole in it should work and a lot cheaper. I think I used a large diameter alum. solid rived (#5) and drilled a .040"hole thru it and pressed it in the AN fitting that attaches to the primer port on the cylinder. The round rivet head prevents it from going farther into the fitting and also prevents it from sliding down the flexible line going to the manifold sensor. Took three minutes to fabricate and install. Cost = 2 cents.
 
Pretty sure a little bushing in your line , clamped in place so it doesn't move and a .040" hole in it should work and a lot cheaper. I think I used a large diameter alum. solid rived (#5) and drilled a .040"hole thru it and pressed it in the AN fitting that attaches to the primer port on the cylinder. The round rivet head prevents it from going farther into the fitting and also prevents it from sliding down the flexible line going to the manifold sensor. Took three minutes to fabricate and install. Cost = 2 cents.

The Garmin install manual specifies that a snubber be used on the MP sense line.
In some installations (including the company RV-10 when the panel upgrade was done) the standard restrictor fitting (which has a .040 diam holes) supplied in the firewall fwd is not enough of a restriction.
 
Phil, 2400 rpm was right in the range where my G3X showed oscillation in MAP - install the snubber referenced by others and you should be good. I got mine from McMaster and placed it at the end of the MAP hose where it connects to the sender manifold on my firewall, the sender for the G3X mounts on the outlet side of same.
 
I've got about 80 trouble free hours with Omega snubber installed directly to the Kavlico sensor which is installed in the stock position (right upper FW). During flight today, the manifold pressure starting acting strange and stopping in various positions (i.e. 8" 23" etc..) I could slowly pull the throttle to idle and then all the way forward and the gauge seemed to recover and read normally...... for 5 minutes. I haven't dug in to the troubleshooting, just yet, but does this sound familiar? Plugging maybe? Just looking for other's experience before I start undoing wire bundles.
 
Yes!! I had the same issue maybe 12-15 months after install. Remove and clean the snubber piece. It was obviously plugged almost completely.

Also added it to my annual checklist to prevet furtehr issues.

E
 
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