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Old 05-22-2022, 11:41 AM
Ed_Wischmeyer's Avatar
Ed_Wischmeyer Ed_Wischmeyer is offline
Join Date: May 2005
Location: Savannah, GA
Posts: 1,661

Thanks, all.

Constant speed prop, forgot to say that. But on my old RV-4, fixed pitch wood prop, you could change the manifold pressure a few inches with no change in RPM.

Don't have a mechanical MP gauge and that would be a wildly inconvenient experiment to try, and could only try it on the ground.

Adding more volume to the line to the sensor would help faster fluctuations that I don't have but would make the lag worse.

Probably won't get to flight test till Tuesday, but... at one point, had fuel pressure problems and changed the pump. Didn't help, changed the sensor. Still have flakey fuel pressure readouts that I ignore, but I am careful to check the electric fuel pump before engine start.

But the engine runs fine...
RV-9A at KSAV (Savannah, GA; dual G3X Touch with autopilot, GTN650, GTX330ES, GDL52 ADSB-In)
Previously RV-4, RV-8, RV-8A, AirCam, Cessna 175
ATP CFII PhD, so I have no excuses when I screw up
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Old 05-22-2022, 12:22 PM
gasman gasman is offline
Join Date: Mar 2007
Location: Sonoma County
Posts: 4,393

Originally Posted by Finley Atherton View Post
I had this wandering MP issue with an MGL XTreme and solved it by adding more air volume in the MP line to dampen the fluctuations. Initial testing was temporarily installing an extra about 8 ft ?? of 1/4” ID plastic tube in the MP line aft of the firewall which stopped the fluctuations. Permanent solution was installing a pulsation damper from my junk bin in the MP line but anything that increases the air volume of the MP line would work.

Fin 9A.
Interesting. I also have the XTreme and connected it to #3 with a brass barb and the line supplied with the unit. The line goes from #3 up to the motor mount where I installed a restrictor. The line then goes down to the RDAC and is a push on connection that is mounted on the face of the battery. No fancy fittings, no fancy teflon lines, just the same vacuum line used on cars for almost 100 years..... Display is solid and stable.

Back to Ed's issue.... With both manifold and fuel level issues, I would look for a bad ground.
VAF #897 Warren Moretti
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Last edited by gasman : 05-22-2022 at 12:28 PM.
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