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Manifold pressure gauges keep dieing

A

agent4573

Well Known Member
Full g3x system, gea24, all Garmin sensors. Coming up on the 2nd annual and my 2nd manifold pressure gauge is on its way out. If the manifold pressure is less than 10-12", the g3x gauge goes to zero. If it stays there long enough I'll get a red x which goes away when the throttle gets pushed back up. It normally seems to be accurate when the MAP is 20" or higher, but today I was doing stalls and noticed the g3x was reading 15" while both my SDS gauges were reading 25". This is the 2nd time this has happened, and the first time I replaced the sensor and checked all the lines and connections for an air right seal. I didn't find any leaks or damage and the problem seemed to go away for a few months after replacing the sensor.

I run a 3an line off cylinder 4 to the Vans provided firewall sensor tree. The restrictor elbow is mounted on the bottom of the tree. The sensor is on the top. Is having the restrictor that close to the sensor killing the sensors? I would really like to solve this one at annual later this month.
 
agent4573 said:
Full g3x system, gea24, all Garmin sensors. Coming up on the 2nd annual and my 2nd manifold pressure gauge is on its way out. If the manifold pressure is less than 10-12", the g3x gauge goes to zero. If it stays there long enough I'll get a red x which goes away when the throttle gets pushed back up. It normally seems to be accurate when the MAP is 20" or higher, but today I was doing stalls and noticed the g3x was reading 15" while both my SDS gauges were reading 25". This is the 2nd time this has happened, and the first time I replaced the sensor and checked all the lines and connections for an air right seal. I didn't find any leaks or damage and the problem seemed to go away for a few months after replacing the sensor.

I run a 3an line off cylinder 4 to the Vans provided firewall sensor tree. The restrictor elbow is mounted on the bottom of the tree. The sensor is on the top. Is having the restrictor that close to the sensor killing the sensors? I would really like to solve this one at annual later this month.
Click to expand...
My MP sensor died at about 390 hours. Fortunately, it is an easy replacement because the wires are in a plug. No rewiring required! 🤗
 
Your G3X system supports many different manifold pressure sensors, produced by various manufacturers... which one do you have installed?
 
mburch said:
Your G3X system supports many different manifold pressure sensors, produced by various manufacturers... which one do you have installed?
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  • 494-30004-01 Manifold Pressure, 30 PSIA, 1/8-27 NPT
It's the Garmin labelled P4055 sensor. The original came in the 4 cylinder Garmin EIS bundle. The 2nd was an aircraft spruce replacement based on the part number above that's advertised as a Garmin part. The one I buy next might not be a Garmin part though if there's a better option out there.

www.aircraftspruce.com

Garmin G3X Manifold Pressure 30 Psia Sensor Kit | Aircraft Spruce

Garmin G3X Manifold Pressure 30 Psia Sensor Kit Garmin G3X Manifold Pressure 30 PSIA 1/8-27 NPT Sensor Kit.
www.aircraftspruce.com www.aircraftspruce.com
 
agent4573 said:
  • 494-30004-01 Manifold Pressure, 30 PSIA, 1/8-27 NPT
It's the Garmin labelled P4055 sensor. The original came in the 4 cylinder Garmin EIS bundle. The 2nd was an aircraft spruce replacement based on the part number above that's advertised as a Garmin part. The one I buy next might not be a Garmin part though if there's a better option out there.
Click to expand...
I haven't heard of the Kavlico P4055 manifold pressure sensors having too many problems; I have one in my airplane. According to Table 21-1 in the current G3X installation manual (revision AU) there are other ones you could try, such as this.
 
Is the line leading up to the sensor going uphill to prevent fuel and liquid from migrating down the line and into the sensor? I’ve seen dye from the fuel get into the line… also how is the sensor attached? Cushion clamp? Prop balanced to remove vibrations?
 
This shows the routing. The stainless line comes off cylinder 4. Run mostly level for ~6 inches, then heads uphill to the sensor tree on the firewall. The 45 degree fitting that it attaches to in the sensor tree is the vans VA-128 restrictor fitting with a 40 thou hole. Both the fuel and oil sensor are mounted on the sensor tree and neither of them have given me any problems.

Prop is balanced, I think I stopped around 0.06 IPS which isn't perfect, but is well withing the tolerance for a "good" balance.
 

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I just had my first manifold pressure sensor die on me, and I only have 85 hours on it. In level flight, at 23 squared, the number on the G3x screen would wander up and down first from 22 to 24, then, over time from 20 to 26. It first began to happen on a bumpy day, and I dismissed it as something resulting from very choppy outside airflow or pressure. But then it started to happen in smooth air at a constant speed. Similar to the above poster, my line comes off the rear left cylinder (#6) and generally slopes uphill until it connects to a sensor block mounted to the firewall, along with the oil and fuel pressure sensors. I checked for leaks and had the same problem, then flushed the line with isopropyl and it drained clear. An A/P happened to stop by, and he said that I should just replace it. Electonics die, even new ones. I swapped it out and have only taken one short flight so far, but MP was stable with the new one.

The only explanation I can come up with for why it died so quickly is that this one is the closest to the oil cooler and oil line. Is it possible that the heat ruined it? The sensor is rated to +125C, and I've never seen the oil get much above 180F. Seems to me like the area behind the engine and baffling, and in front of the firewall, should be in an okay temperature range for the sensor, but maybe something is hotter than measured? All of my hoses are fireshielded, so they really shouldn't be leaking much heat.
 
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