Low fuel pressure

[NotarPilot]

Should these readings concern me? It usually starts out slightly above/touching the lower red line in cruise but bumps a tiny bit up after a while. Any thoughts? Is my plane talking to me or is this normal?

Thanks,

Steve

 

[Hank]

Mine occasionally varies in flight but stays in the green. Although at a fraction of your injected pressure!

Do you run your electric pump prior to engine start? Does it achieve max pressure then? Mine does, a whopping 6 psi.

Second question:  after achieving peak pressure (of whatever value), does the pressure hold steady before you move the throttle and turn the key?

[capthaak]

I'm looking at the oil pressure

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[NotarPilot]

3 hours ago, Hank said:

Mine occasionally varies in flight but stays in the green. Although at a fraction of your injected pressure!

Do you run your electric pump prior to engine start? Yes I do, I run it for 3 seconds prior to start.

Does it achieve max pressure then? Mine does, a whopping 6 psi. No, it gets to about mid green while the electric pump is running.

Second question:  after achieving peak pressure (of whatever value), does the pressure hold steady before you move the throttle and turn the key? No, the fuel pressure drops back down when I turn off the electric fuel pump (before engine start).

 

[NotarPilot]

53 minutes ago, capthaak said:

I'm looking at the oil pressure

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The oil pressure is fine. I have an Insight G3 engine monitor which was installed in 2012 and I trust over the 38 year old panel gauge. 

[Marauder]

The oil pressure on my F will sit around 75 PSI. When I had the factory gauge it would show this:

I know the 75 is right since both the JPI 830 and later the 900 using different probes were in the same range of each other.

As for the fuel pressure. It may be the gauge. My fuel pressure was on the round gauge with the MP. It agreed with the EI and the JPI units. And both were 23 PSI in flight.

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[Hank]

My fuel pressure is also on the round MP gauge. I run the pump until it stabilizes, right at the top of the green, then shut if off. It doesn't move unti I touch the throttle. While I could certainly believe the gage is old and tired,mid be surprised if both the fuel pressure and oil pressure gages developed the same issue at the same time.

[mooniac15u]

With both oil and fuel pressure reading low you might have a grounding issue.  These gauges measure resistance in the sensors but they are sensitive to resistance in the entire system.  You might want to check the main airframe ground back at the battery. Even a small amount of oxidation where it attaches to the airframe can cause low readings in those two gauges and high readings on the oil temp and CHT gauges. 

[Yetti]

The test is what happens when you turn on the electric pump.  If it jumps to the white line then time for a mechanical pump.

[NotarPilot]

 

15 hours ago, Yetti said:

The test is what happens when you turn on the electric pump.  If it jumps to the white line then time for a mechanical pump.

Yeti,

You're referring to the white line under the "25" correct?

[Yetti]

Yep.  that looks to be more "normal"  operating zone.   It should go up a little with the boost pump(assuming the boost pump is working) If it jumps a little when you turn the boost pump on, then it is the gauge if it jumps alot then it is the mechanical pump.   

When you prime the engine with the boost pump does the pressure hold or does it leak down pretty quick?   After annual I took it up to 5000AGL and saw the pressure do a jump, came down and did a leak down test on the ground.  A new pump for me.

[Marauder]

54 minutes ago, Yetti said:

6 hours ago, NotarPilot said:

 

Yeti,

You're referring to the white line under the "25" correct?

Yep.  that looks to be more "normal"  operating zone.   It should go up a little with the boost pump(assuming the boost pump is working) If it jumps a little when you turn the boost pump on, then it is the gauge if it jumps alot then it is the mechanical pump.   

When you prime the engine with the boost pump does the pressure hold or does it leak down pretty quick?   After annual I took it up to 5000AGL and saw the pressure do a jump, came down and did a leak down test on the ground.  A new pump for me.

If you are looking for numeric values. I have been running an EI F5PL fuel totalizer since the 1990s on my F. It agreed with the factory fuel pressure gauge considering you are looking at an analog and comparing it to a digital value. For the last two years I also have had the fuel pressure reading from a JPI product.

When I do a cold start with the mixture rich, when I turn on the boost pump it will go to 27 PSI on all 3 gauges. After start, it will go to 24 PSI. When I take off and turn on the boost pump, full throttle, I will see 26 and some change on the JPI/EI units. When I shut it off, the pressure will settle in around 24 PSI. Give or take a few tenths.