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Another Fuel Gauge/Pressure issue

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Well-Known Member
Apr 9, 2010
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Hi all, need some advice/input/information ...


- The fuel pressure needle oscillates/vibrates at a lower than normal pressure, saw between 2 and 3, instead of the usual steady between 4 and 5.
- It does this on run up, take off roll, or during climb. It does not do it every time, it's very inconsistent.
- Turning on the electric pump does not have a consistent effect on it, sometimes it helps, sometimes not.
- In both cases I've observed it, I level off, bring the throttle back, it gets back to normal, never returns after that.
- It seems the length of period of rest between flights may be a factor, I did 3 2 hour flights in 2 days, and the problem didn't re-appear after the very first time int he first flight.
- After sitting for a week, it appeared on take off.
- Another pilot noticed it on run-up, elected not to fly. Can't blame him.
- This started a couple of weeks ago ... no notable event occurred at that time.

My thoughts:

- I don't imagine the fuel pressure transducer would notice such rapid fuel pressure fluctuations as to cause the oscillation/vibration in the needle. it shakes.
- So I'm more tempted to think it's a wiring or gauge issue, possibly related to the vibrations and high RPM during run-up, take off and climb. Visually and instinctively, it really looks like the needle is vibrating with the engine ...
- Or maybe there's a "warming up", but the fact levelling off and closing the throttle from WOT fixes it every time suggests it'S not just temperature. RPM, or attitude or something like that seems like a better correlated contributing factor. Maybe the fuel pump has a hard time "sucking" fuel in at first, but warms up?

- Ever see something like this? Have the problem? Do you happen to know what the cause/solution for you?
- Am I off the ball thinking the actual fuel pressure in the lines couldn't be fluctuating the way the gauge indicates it?
- If so, and it's possible the fuel pressure is indeed a little low in some circumstances, would it just be the pump about to die, or could it be something else?
- Are engine fuel pumps known to have a smaller MTBO than say the engine itself? (I would imagine so ... for instance vacuum pumps are said to have about 500hours of life in them ... are fuel pumps the same?)

Thanks in advance for the great insight, as always!

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