Manifold Pressure will not come down

[crxcte]

My manifold pressure will not come down after I pull the power.  Anyone have to replace this instrument or know of a repair?

[sleepingsquirrel]

It could be a loose fitting or broken line. Line could be plugged. Does it sometimes look like it's working? Just not showing change with throttle?

[crxcte]

Yes, it looks like it works on the high side, like during engine take off but when I pull the power it is not falling below 25 inch Hg.  I looked on the engine side and the pressue line looks OK, not broken.  It does fit the clogged line possiblity.  I'm thinking the manifold pressure dial is like a barometer sensor and the line to the cyclinder is like the line to the vent.  Never had any problems with this before.

[Piloto]

Quote: crxcte

Yes, it looks like it works on the high side, like during engine take off but when I pull the power it is not falling below 25 inch Hg.  I looked on the engine side and the pressue line looks OK, not broken.  It does fit the clogged line possiblity.  I'm thinking the manifold pressure dial is like a barometer sensor and the line to the cyclinder is like the line to the vent.  Never had any problems with this before.

[takair]

I think you have a brass line from the firewall to the 3 cylinder (?).  This frequently fails near the #3 cylinder.  If you are lucky you can open the oil door and follow it for much if it's FWF length.  Look for chaffing as well, especially near the baffles.

[crxcte]

Yes, runs to the #3 cylinder.  Need to look a little closer and the condition looks like all is connected. 

I see from Jose's comments, it should be a leak since the outside pressure is around 28 inches and I can't get below 25 inch. My plane can fly at 15 inch (vacuum range) manifold pressure and keep level flight.  That would be a pretty good leak.

[N601RX]

I've noticed that the gasket around the glass on ours is starting to come out and is almost scrubbing the needle.  I suspose it coould jam the needle.

[jetdriven]

An instrument shop can overhaul that for you, and calibrate it as well.  I imagine there are a lot of Mooney pilots on here that say how they can get XX GPH on 25" of MP, but their plane is a little slow also..  Between that and the tach instead of running 25"-2500 they are 23"-2400 RPM.  

[piperpainter]

I had my line cracked after takeoff it was right in a bend and wasn't really visible. I replaced the line it was easy and relitively quick....once I found the line! This happened last summer while I was over on the East coast....on a saturday. Thankfully I landed at Hampton field and they are awesome there!

[carusoam]

My 65C cracked the aluminum tube right at the calibrated leak hole behind the instrument.  If you replace the line, be aware of the need for the is tiny hole.  It is only a foot note in the mooney parts drawing.

 

-a-