Manifold pressure fluctuation

[Glen Davis]

The manifold pressure in my 1989J model fluctuates. This is being displayed on a Garmin G3X. What might be causing this? No other anomalies on any other instruments or gauges.

[IvanP]

12 minutes ago, Glen Davis said:

The manifold pressure in my 1989J model fluctuates. This is being displayed on a Garmin G3X. What might be causing this? No other anomalies on any other instruments or gauges.

Can you identify any patterns of this indicated fluctuation? Do you have a secondary MAP indicator for reference? It could be some interference with the sensor data transmission that could cause the indication to fluctuate when, in fact, your MAP may not. 

I have exprienced similar situation with JPI 900 - my MAP indication on the JPI goes up every time I transmit on the radio. The old fashioned  MAP gauge next to the JPI is rock steady. After spending quite a bit of time on troubleshooting, adding shielding to wires, etc., to no avail, I gave up and learned to live with this little gremlin. 

[Will.iam]

19 minutes ago, Glen Davis said:

The manifold pressure in my 1989J model fluctuates. This is being displayed on a Garmin G3X. What might be causing this? No other anomalies on any other instruments or gauges.

Fluctuates all the time, at idle, at full power? 
if all the time i would suspect a ground issue first. 

[Skates97]

 If it is a constant fluctuation of 0.5 you may need a snubber in the line. The electronics are much more sensitive to minor fluctuations than the old gages.

 

[201Mooniac]

As Richard points out, it could be needing a snubber, many who go to electronic instrumentation find they need it.  If so, let me know, I have one or two around.

[TheAv8r]

36 minutes ago, Skates97 said:

 If it is a constant fluctuation of 0.5 you may need a snubber in the line. The electronics are much more sensitive to minor fluctuations than the old gages.

 

+1 this fixed it for my 930. 

[shawnd]

Isn't the software supposed to compensate for the fluctuations / pulsing of air to the sensors? Wondering why Garmin doesn't just indicate this in their installation manuals. 

[Ragsf15e]

15 hours ago, shawnd said:

Isn't the software supposed to compensate for the fluctuations / pulsing of air to the sensors? Wondering why Garmin doesn't just indicate this in their installation manuals. 

You would think, but the first thing JPI recommended to me was a snubber.  I think it’s an Omega 8g but you better check sizing.  Mine fixed my 930. Easy to install too.

[Skates97]

As @Ragsf15esaid, yes it should and they said it did as of some version update. Mine was a newer version of the software than the one that supposedly fixed it. Still had that constant fluctuation but the snubber did the trick. 

[Ragsf15e]

10 minutes ago, Skates97 said:

As @Ragsf15esaid, yes it should and they said it did as of some version update. Mine was a newer version of the software than the one that supposedly fixed it. Still had that constant fluctuation but the snubber did the trick. 

Yeah, mine is updated sw as well.  Weird how it’s “not solvable” by sw. I’d think it would be pretty straightforward.

[shawnd]

Yeah, in the worst case, I would say an intro interview coding question of moving averages can resolve the issue "through software".

[A64Pilot]

On 8/29/2024 at 4:41 AM, shawnd said:

Isn't the software supposed to compensate for the fluctuations / pulsing of air to the sensors? Wondering why Garmin doesn't just indicate this in their installation manuals. 

Some do, some don’t Electronics International does, I believe they call it “smoothing”. Piper on their turbines the gauges have a “snap” function I was told, when they get to normal, they snap into a reading and stop wandering around.

Without something digital gauges last digit would often be a 8 which is what you get from rapid tiny fluctuations.

[jetdriven]

We put a snubber on a MVP50 fuel pressure and it damped it right out. It previously was always all over the place.