Fluctuating Manifold Pressure

PhantomPholly

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Jul 27, 2007
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I have a D-180 installed in a Lancair 320 with an IO-320.  All new hoses with AN fittings between the MP takeoff port on the engine and the Dynon sensor, and in any event leakage does not appear to be the problem.

The reading on the screen rapidly fluctuates +/- 1".  Is this "normal?"  Is there a way to smooth it out (perhaps with a small accumulator bottle?), and will doing so result in an accurate reading?
 

dynonsupport

Dynon Technical Support
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This is somewhat normal, and reflects real fluctuations occurring in the engine. A restrictor between the engine and the MAP sensor will damp it out and not mess up the reading. It needs to be very, very restrictive. Some people have had luck with cigarette filters or tightly packed foam. You can search the forum for more ideas and there is also some info in the install guides.
 

Roger_Lee

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Aug 1, 2006
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The Flight Design Ct's put a Bing carb idle jet in line in the MAP hose. This tiny holed restriction works perfect. The MAP pressure is as steady as a rock and the idel jet doesn't affect the reading. I works great.
 

Thomas_Schaad

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Mar 23, 2005
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You can also put a simple cigarette filter in the MP-line, it worked out perfectly.

Kind regards

Thomas  ;)
 

N8RV

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Nov 30, 2006
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You can also put a simple cigarette filter in the MP-line, it worked out perfectly.

Kind regards

Thomas  ;)

OK, so I had the same issue. I put a cigarette filter in the MAP line and it indeed damped the fluctuations and gave me a solid reading.

Then, the other day, I noticed that the MAP reading was starting to fluctuate rapidly again. I pulled the cowling (time for an oil change anyway) and looked at the cigarette filter -- it was beginning to come apart. Looked like the middle was being sucked out of the filter.

My big question is, naturally, what is the likely outcome of having cigarette filter fibers being sucked into a cylinder? Nothing, as it will be burned during combustion? Or, could it cause the valve to stick and have serious consequences?

Anybody know?

I think I'll switch to foam now ...
 

N8RV

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Nov 30, 2006
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Well, having heard nothing about what happens to a cigarette filter if it gets sucked into an engine, I pulled the cowling tonight to check on the status of the disintegrating filter.

Umm ... it's gone. POOF.

I removed the MAP line and checked to see if it was clogged, but it wasn't. Nowhere to be found. So, I cleaned the line and made a restrictor out of a plastic sleeve and a rivet with a small hole drilled in it. It can't go anywhere. I'll find out if the hole is small enough the next time I crank up the engine.

Moral of the story: DO NOT USE A CIGARETTE FILTER AS A MANIFOLD PRESSURE DAMPER!! :eek:
 

meljordan

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Mar 23, 2005
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My damper is two male nylon barb fittings screwed into a nylon coupler with some foam rubber compressed into the cavity. This has been working for almost a thousand hours with no problem.

Mel Jordan
 

DBRV10

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try jamming some high density foam door sealing stuff in the tube at the sensor end, away from the engine etc and upstream of a restricting fitting, that way nothing will move to where it should not.
 

16FW

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May 6, 2009
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Foam disintegrates over time too. If you do use foam, replace it every couple of years. Fibreglass mat might be another thing to try.
 

Jerrylane

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It is not wise to place anything in the line that can be inadvertently drawn into the intake system.  If you are using AN fittings to connect to the intake manifold you can use a small aluminum machine screw with a drilled out center and the head filed down to just larger than the AN fitting.  I used a phillips head and was able to thread it into the AN fitting insuring it cannot get loose it is then locked under the tubing ferrel and nut.  Use a very small drill to drill out the machine screw and then trim it to about 1/4 inch in length not counting the head, screw it into the fitting and then file it down so the ferrel and nut will fit over without interference.  Hope this helps. :)
 

N927BC

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I have 2 Skyview display with engine monitor and my manifold pressure is erratic at times. I just replaced the manifold pressure sensor and I still have the same problem
 

Dynon

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In that case, I'd start looking at connections upstream of the sensor for an intermittent connection. Which way does it go?
 

dynonsupport

Dynon Technical Support
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What engine do you have?

Some engines have the MAP sensor port located very close to a cylinder and the MAP sensor registers the "slap" of the cylinder. Some customers have had success in installing a restrictor in the pneumatic line going to the MAP sensor.

This normally isn't an issue in SkyView systems, only our older EMS systems.

I have 2 Skyview display with engine monitor and my manifold pressure is erratic at times. I just replaced the manifold pressure sensor and I still have the same problem
 

kurtfly

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Jun 21, 2014
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On My Glasair with a LYC IO360 I have been using a brass 1/8 NPT fitting on the #3 Cyl. This fitting I sealed completely closed by soldering it shut with a propane torch. Then drilled a #60 hole thru the solder. By having the orifice near the engine allows the tubing between this and the MP sensor act as a dampener. I have been using this for over 15years with no problems. I have never had any MP fluctuations with SV or my previous EI gages.
 

Robski

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Nov 29, 2015
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I had this problem when I first installed the EMS D-120 late last year.

Fixed it by turning myself a brass restrictor on my lathe and inserting it in the hose between the cylinder and MP sender. Put it in the cylinder end of the hose.

OK - not earth shattering news in itself!

You may be interested on sizes. The brass restrictor was 1/4" diameter x 1/2" long and the all-important hole was 1mm, or 0.040" in English.
The advantage of something large and solid is there's no way that is going to get sucked into the cylinder!

What is most interesting though is that I bought the MPS and EMS from a friend.
He had it on an IO-360 and didn't need a restrictor. He ran it off Cylinder #2 so the hose was around 2 feet long and had a 180 degree bend in it.
I put it on an O-320 running it off Cylinder #1 so the hose was straight and just over 1 foot long. My installation needed the restrictor.

What factor makes the difference, or whether it is a combination of factors I can't say, but I fixed that sucker good!
 
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