Manifold Presure Issue

[Arlingtonrv]

I have searched and not seen this issue mentioned. I have a 10" Skyview in a Glasair Sportsman with an IO-375. For the last dozen or so flights I have had this issue, but it did not show up in earlier flights.

On engine start the Manifold pressures reads pretty high, usually above 29". At takeoff it reads 35-36 inches and moving the throttle has no effect on the pressure. After about 5 minutes it settles down and reads normal for the remainder of the flight. All other indications and parameters are normal.

I's this likely just a wonky pressure sensor or is something more sinister likely to be afoot?

The engine and Skyview system has about 40 hours total on them and this started after the first 15 or so.

Thanks

Steve

 

[Dynon]

35-36" is above ambient, which isn't really possible unless there's an obstruction or crimp or something that's holding air against the sensor that then heats up and expands after the aircraft has sat. So I'd probably investigate that possibility, but beyond that, it sounds like a sensor issue. Especially if it did work normally for the first 15 hours.

 

[dynonsupport]

Another possibility is water or other liquid in the line to the MAP sensor. Easy check is to disconnect the line from the MAP sensor. It should read just below the BARO setting there in Arlington.

 

[Arlingtonrv]

Thanks for the ideas. To make matters worse, it worked perfectly yesterday. I'll try cleaning out the line to the sensor and see if I can find anything.

Thanks

 

[jakej]

Steve, is the map sensor at a much higher level than the cylinder pickup point ? It should be

 

[Arlingtonrv]

No, actually it is mounted relatively low on the firewall, a good foot at least lower than the cylinder.

Thanks

 

[jakej]

At least now we know what caused the issue - suggest you mount it as high as you can, maybe use p clips onto the top tube of the engine mount - that's what I did with my Glasair & on other installations I've done.

The MAP sensor may be u/s now but mount it higher & see how it works out, worse case is replacement of it.

 

[Arlingtonrv]

Thanks for the information. Where does this suggestion come from? The Dynon installation instructions don't say anything about where to mount the sensor.

Thanks

 

[jakej]

Thanks for the information.  Where does this suggestion come from?  The Dynon installation instructions don't say anything about where to mount the sensor.

Thanks

From me actually    based on my experience (installations on approx 60 aircraft), commonsense & through knowledge gained by reading about what manufacturers recommend.

Dynon & others are not in the business of telling you how to build an aircraft.
IMO their install manuals are to be used as a generic guide as to how to connect& configure all the 'boxes' you buy from them, they can't be expected to cover every combination of equipment you install especially when other third party items are included in the mix.  Install Manuals are now 400 + pages, we don't need them bigger

You are building an 'Experimental' & part of the EAB community, it's all about learning new skills - I'm still learning too

 

[n456ts]

It's also standard in the auto industry (for older cars with remote MAP sensors). Detroit Diesel had a recall over a very similar issue with their EGR delta-p being mounted too low allowing water build up. They all got relocated.

 

[Arlingtonrv]

Just wanted to provide an epilogue and thank everyone for their help. When I took the old sensor out it was indeed contaminated with something (as hypothesized by Dynon Support in reply #2), I think it is residue from the dye in the fuel.

I replaced the sensor due to the above mentioned contamination and moved it to a location above the cylinder. In 2 flights this weekend it has worked flawlessly.

Thanks