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0360-A1A, what is normal fuel pressure

stringbender

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I was wondering what is the normal fuel pressure developed from the engine driven pump? Also what fuel pressure should you see when turning on the electric pump to back up the fuel system say for landing?
 
From the Lycoming manual that came with my O-360-A1A, fuel pressure:
Max = 8 psi
Desired = 3 psi
Min = 0.5 psi
 
Mine normally runs in the 4 to 4.7 range except when the fuel has been cold soaked overnight when it can get as low as .8.
Figs
 
I was wondering what is the normal fuel pressure developed from the engine driven pump? Also what fuel pressure should you see when turning on the electric pump to back up the fuel system say for landing?

"Normal" is a very elusive term when it comes to the O-360-A1A fuel pressure. It's a much discussed topic here and you can search for other threads on the topic on this site. I don't know if it's Vans suggested placement for the pressure senders, or the geometry of the fuel lines, etc. but you may well see the high, average, and low readings (8.0, 4.0-5.0, and 0.5 psi) all on the same flight.

My heart almost stopped the first time I looked down at the pressure gauge while climbing out at takeoff (fuel pump on and engine pump working) to see just about 0.0 on the gauge - I thought I was in real trouble. Then I realized the engine was running just fine. So all I can say is that typically (not normally :)) the needle should be in the green arc for cruise flight. If you see it drifting during flight, I suggest you verify the gauge ground is good. Early in flying my RV-8, I discovered that if I laid my hand on the cover plate where the fuel gauge is attached, the reading would change. That indicated a poor ground which I fixed by rerouting the ground wire to the left longeron rather than attach it to the aluminum support piece that holds the gauge cover.

No doubt there are number of factors that may affect the reading including altitude, temperature, etc. that may affect fuel pressure, but be encouraged by the fact that this engine needs very little pressure to work properly.

If you find a solution for this mystery, please share. I'd love to know.

Chris
 
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