Manifold Pressure Fluctuations

[Bob(Guest)]

Hi,

My manifold pressure fluctuates wildly. (eg. 17-27 in during cruise) All phases of flight there is this wild rapid fluctuation.
It is firmly bolted to the firewall and a 1/4 hose connects to 1/4 aluminum pipe to an AN fitting on the O-320. Pipe clamps are at both ends of the hose. Engine has a carburetor.
The wires seem to be attached well. With the engine off it reads steady.
Is this a defective sensor and do you have any ideas on further troubleshooting.
Thanks Bob

 

[dynonsupport]

Bob,
We have seen this before. I don't think it is a defective sensor. I believe the pressure at the sender is actually doing this, and we are faithfully showing it to you. The vast majority of our customers report totally solid readings, but a few have mentioned this issue. We're not sure why one engine would have such large variations while others would be so stable. Could you tell us where your MP line connects to the engine?

In any case, we are working on software to filter this out. Hopefully we can have something to you soon. If you would like to try something mechanical as a solution, I would suggest trying a restriction in the tube leading to the sender, close to the MP pickup on the engine. This would dampen the pluses going to the sender.

 

[ghostriver]

Hi,

The MP line connects at the forward right cylinder with an AN fitting at the primer position. The other three cylinders have primer lines.

I will try a restrictor, a rivet with a hole in it at the compression end of the fitting, and let you know the results.

Thanks, Bob

 

[ghostriver]

Hi,

The restrictor has significantly reduced the fluctuations. About +/- 1 psi.
Thanks,
Bob

 

[Don J.(Guest)]

I would think that taking the MP reading off a single cylinder would cause the fluctuation. There is a little overlap where both valves are open and being that close to the valve might be a problem. I may be totally off base on this though.

Don