Temporary Low fuel pressure fluctuations

[PT20J]

16 minutes ago, gabez said:

for me was the fuel vapor check valve. the vapor couldn't go back into the tanks and the pump eventually couldn't push fuel. High fluctuations same graph as urs. 

Different fuel systems, though. The Lycomings don't have a fuel return line.

[PeytonM]

I have the G3X EIS and have seen the wild fluctuations ever since the installation 350 hours ago.  FP at zero for minutes at a time, even at startup. Fuel flow is fine, and engine runs perfectly. We replaced sensor, installed snubber to no avail. Boost pump, switching tanks, no change.

According to a company who regularly collects engine data, JPI devices will see it, but much, much less frequently than Garmin, and usually snubber fixes it for JPI. One of long-body drivers here solved a connection contamination using contact cleaner, but mine are the Garmin environmental connectors, so no joy. I have given up.

[PT20J]

I forgot to mention that I also installed a snubber to no effect. I had the factory gauges on the new engine for a couple of years before installing the G3X and never saw this. My conclusion is that the fluctuations have always been there, but the mechanical gauges were much more heavily damped and we didn’t see it. I too have given up trying to change it and just ignore it. 

[PeytonM]

Kinda sad that you spend $$$ and you end up with this. And Garmin just throws it back to the installers. Sound familiar??

[gabez]

22 hours ago, PT20J said:

Different fuel systems, though. The Lycomings don't have a fuel return line.

where does the vapor go? (out of curiosity)

[PT20J]

18 minutes ago, gabez said:

where does the vapor go? (out of curiosity)

During operation it will either pass harmlessly through the servo or be bled out the vapor bleeds within the servo. After shutdown, it depends on how tight the mixture plate seals. If there is some leakage, it bleeds off through the injectors. If the plate seals tightly, it stays in the lines and you will notice it from the sound of the boost pump when you next prime.