High Fuel Pressure Investigation - Part 3
TLDR
- Continue from Part 1 & 2; Investigaing the high fuel pressure issue
Details
This is a combined update from the last two days. I’ve been working on the high fuel pressure issue. Here are a list of things I’ve done.
Fuel selector check valve
When I was rebuilding the fuel return lines under the fuel selector, I also installed the check valve between the main return line and the left tank return line. I’ve been debating whether I should do this, and decided now is the best time since everything ws torn open.
Testing Again
However when I turned on the pump after reconnecting everything, the fuel pressure stayed absolutely the same as before.
I guess it’s not surprising, because I previously disconnected the line from the engine return port directly, and it was 47 PSI. So the pressure is already too high before even coming out of the engine. The best I can do with the return lines is that it should not make it worse.
Inspection Found Fuel Leak
Yesterday I connected the rebuilt rubber fuel hoses to the engine, and today I found a fuel leak before testing the engine again. The access was fortunately easy, so I just tightned it another 1/8 turns.
Redoing the Manifold Air Hose
I also bought some slightly smaller ear clamps (10mm) to replace the ones I currently have (10.5mm) on the manifold air hose, although I highly doubt that’s my problem.
While I was redoing the clamps, I also rerouted the air hose just to be sure there is no kink.
Test Engine Run
So the next test I did this afternoon focused on higher RPM runs.
My theory: Midwest told me they’ve seen 47-50s PSI when airplane was on the ground. It makes me wonder maybe the high PSI that I’m seeing isn’t really a problem. Maybe it’s truly because of the pump and not some kind of kink in my fuel lines. So if I can run it at higher RPM, maybe the engine drinks more fule, AND the manifold pressure goes up, so the differential pressure can go down a little?
I did the normal engine start-up, and built up the RPM to 4000 RPM. What made me feel better was that the pressure didn’t shoot up like last week.
However, when I approached 4000 PRM the brake no longer held the airplane. I started to inch forward slowly. Either the brake has air bubble in it, or I need to condition the brake. So I guess I have 2 jobs to do: brake AND fuel pressure. Oh well, logged the brake issue in my tracking app.
Shameless plug, here is my maintainenace app SquawkIt if you want to give it a try. I think it’s better than using spreadsheet to track TODOs.
- Android Play Store: https://play.google.com/apps/testing/dev.fanfly.wingslog
- Web: https://squawkit.fanfly.dev
- Apple: Coming soon