vibrating fuel pressure gauge

blueskyMD

blueskyMD

Pre-takeoff checklist
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Mar 26, 2015
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352
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Allentown PA
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Bigfoot297
Since I had this airplane my fuel pressure gauge always vibrates right after start up.The only time it did not do it was after the engine OH in 2008 and it stayed stable but in the lower part of green arc. It lasted only 5-10 hours and since then it kept vibrating fast and went on until last annual when mechanic suggested that constant vibration will damage the gauge and suggested to OH ED fuel pump. We did OH exchange from Tempest last annual in Oct 2016. Once again it lasted about 5-10 hours and now back to constant vibration. Engine had never ran rough in its 1000+ hours of life and no other fuel related issues. I was told that its a common problem in Lance/Saratogas. Any idea whats going on and how to fix it ?
 
Most installations have a restrictor fitting it the fuel pressure line. If it's missing you'll get what you are seeing.
 
Did it in my Lance until I replaced it with the EI CGR-30P ;) The 30P still fluctuates slightly, but nothing like the dancing I saw from my analog gauge. Tried three different gauges and all would do what you describe. They'd be good for a few hours and then start dancing again. Never had a lick of trouble with fuel flow; however, we did swap the fuel pump for an OH unit...same result. It just seems to be a common thing in a few different Piper models. Upgrade to an approved primary replacement engine monitor and remove the analog gauge...chances are, that will solve your problem, lol.
 
What Norman said. Replace the orifice (or add one if there never was one) and the problem will go away.
 
thanks guys.
I will talk to mechanic about replacing orifice. I was highly skeptical about FP fixing the problem but since FP was about 8 years old and had 1000 hours I decided to let it go.
 
Timbeck2 said:
Good post. Have a buddy with the same problem on his Arrow.
Click to expand...
On Arrows this can be as simple as the line to the gauge being completely filled with fuel. It needs some air for dampening. Very simple fix, just drain the line and reconnect, deliberately leaving a bunch of air.
 
I guess these are carb engines? and gauge is dancing in time with the engine driven pump?
 
Its an injected IO 540
And I forgot to mentioned that turning on electric FP does not make any difference
 
Our PA-32 fuel pressure always dances a bit. Just to the green side of where yellow and green meet on it. Wiggles less when the auxiliary pump is on. Very consistent. Have just taken it as one of the things we deal with in an older ('77) plane. Curious if the reading will be rock steady with the snubber above and wonder if the cost to "fix" it is worth the $.
 
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