Fuel pressure after shutdown on IO-360 A1A

Hey guys,

Just replaced my Dynon transducers with the updated Kavlico models, so I've been watching fuel/oil pressures. I've got the standard Bendix RSA-5 setup on my IO-360 A1A. I've updated the Dynon engine maps and put a couple flights under my belt with all pressures looking good while in flight. However, this is the first time I shut the engine down but kept one of the Dynon screens on for about 30 seconds and I watched the fuel pressure slowly climb to around 50psi. If I push in the mixture from ICO it drops to zero and slowly rises again. Since I put all my flights on SavvyAnalysis I went back to check on flights prior to changing out the tranducers. I was able to catch some flights that showed this same trend for a few seconds before the Dynon EFIS shut down. My "***"umption is this is normal due to heat soaked engine increases vapor pressure in the lines. Keep in mind, engine is completely shut down, no pumps operating (mechanical or electrical). I hear the usual vaporization in the lines under the cowling when I open my oil door but that much pressure reading off the transducer? Thoughts? Normal? Abnormal? Can it blow the diaphram on the mechanical fuel pump?

Normal. Mine does that too...

You have mixed a few extra physical effects in there, but it really is the solid expansion of the gasoline that causes excessively high pressure. You probably have a non-vans fuel hose rated at 5000psi and is really stiff expansion-wise. .

The already hot (liquid) fuel is captured between the check valve at the boost pump and the check valve at the mechanical pump. Vapor pressure will not yield pressures anywhere near the trapped solid expansion pressures. I had a project where it reached 300 psi, just due to a 3/8" X 50" hose specification change.

If you installed the new pressure sensor, you are good!

Thanks Bill, yes I have all TS flight line silicone hoses just kinda shocking the first time you see it after shutdown. No leaks anywhere and the giveaway was pressure release when mixture valve opens. Only non TS flight line hose is the standard Vans line to the transducer manifold for fuel and oil. I put this out there for those who are changing out Dynon/Garmin Kavlico sensors just in case they are paying attention and notice the same thing. Like me they will run over to Vans Air Force forum and start searching but nothing directly comes up so I wanted to create at least one thread. Confirmation such as yours really helps so thank you.