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Manifold gauge leaking down?

jerryab

Member
On a cross country flight this week in my RV6A, I noticed my manifold pressure was down to 15 in, but I was still flying at cruise speed. I added full throttle and it resulted in no increase in mp. It had been fine on my departure. When I returned it was fine on take-off, but leaked down again after 20 minutes. I've recently replace the transducer. This is Van's guage. Any thoughts on where I should look. I've already checked the lines at the connnections. This is an O-320 D1A.

Jerry
N331RA
 
My MP gage behaved identically. I could get the gage to go full deflection when I keyed the mike. Then it would go full deflection when I turned on the master switch. Cycle the master and the gage would stay at zero, and never work at all again.
I pulled the whole Vans MP system from the plane and replaced it with an old fashioned mechanical/pneumatic gage and copper tube plumbed directly into #3 cylinder head.
 
Manifold Pressure Indication

I experienced this exact problem with the same equipment except my MP gauge buried itself at 10Lbs. with no loss of engine power on 2 legs of a 500 mile x-country.

I'm puzzled how this much vacuum is developed with no change in engine power. Of course the symptoms disappear after landing and shutdown.

I'm thinking ice but, beats me how it gets there and causes that sort of indication.

Anyone have any ideas?
 
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