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  #11  
Old 01-28-2018, 08:07 PM
Timberwolf Timberwolf is offline
 
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I?ve been seeing the same fuel pressure fluctuations on my g3x with my A1A as well. Engine runs fine so I?ve been ignoring it for now. Flipping on the boost pump bumps the pressure back up but engine never stumbles. I?ve seen fuel pressure drop while in the climb or while on the ground, it never straight and level flight
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  #12  
Old 01-28-2018, 08:12 PM
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RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by jonweisw View Post
The reason I know it was a failure of the pump and NOT the transducer is that when the dips would occur they could be easily remedied by activating the electronic auxiliary fuel pump. The pressure would return to around 28 psi.

While I may not actually be getting 32-34psi from the new pump because the transducer hasn't been calibrated, it is worth noting that it is 10psi higher than it was reading nominally on the older pump (22psi) and there are no dips.

So, while it may not have truly hit 14psi in the dips (because the transducer wasnt calibrated), the mere fact that it was running half the pressure of what the aux pump could produce and that it was a departure by 40% of baseline was enough for me to change it out. Not worth waiting until complete failure IMO.
I'm not trying to be disagreeable, only to apply engineering methodology here...all you know is that when you turned on the auxiliary pump, the pressure as indicated went back up. The transducer could have a failure mode that makes it non-linear in response, the auxiliary pump could clear another fault somewhere in the line, etc.

Unless you have a *root* cause of the failure, you don't know for sure what caused the drops...
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  #13  
Old 01-28-2018, 08:16 PM
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RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by jonweisw View Post
There is another thread now that is exploring the transducer possibility as an explanation that should be very interesting. In the meantime, here's a screenshot of a typical excursion (G3x data dump to saavy analysis)..

This has a very similar profile to the excursions I've seen...steep drop for the initial portion, slightly less steep after that, minimum, then rapid climb back up to normal. This looks slightly longer in duration than the ones I've seen, though, which are on the order of just a handful of seconds.

I'll try to find one to post an image, but as I said, it's rare enough (3-6 months between them on average) that it'll take me a while to find one.

BTW, I've seen them in stabilized, straight and level flight, not correlated to pitch or roll changes, switching tanks, or turning on/off the boost pump.
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  #14  
Old 01-28-2018, 08:26 PM
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Alright, here's one that happened at 27:15 into a flight.

https://www.savvyanalysis.com/flight...e-2e37e0e34408

Savvy could find nothing to correlate it to (I submitted a ticket to them for analysis).
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  #15  
Old 01-28-2018, 08:58 PM
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AlexPeterson AlexPeterson is offline
 
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Quote:
Originally Posted by RV7A Flyer View Post
Alright, here's one that happened at 27:15 into a flight.

https://www.savvyanalysis.com/flight...e-2e37e0e34408

Savvy could find nothing to correlate it to (I submitted a ticket to them for analysis).
I?ve had exactly that sort of experience. Seems like a stretch to blame it on a simple mechanical fuel pump.
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  #16  
Old 01-29-2018, 06:56 PM
Boyd Birchler Boyd Birchler is offline
 
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Never had a Lycoming pump fail! That is with 6000 plus hours of owing 20+ (Only 16 had lycomings) airplanes. Only mechanical pump I ever had fail, was on a Rotax 912, there was a service letter about this particular pump, saying it was prone to problems, and it did have that problem.
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  #17  
Old 01-29-2018, 07:40 PM
hudgin hudgin is offline
 
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Check out your Lycoming Engine Operators Manual. Your engine should put out max 35 psi to a minimum -2 psi. That's negative 2 psi. So the issue is not fuel pressure but fuel flow. As long as there is a fuel flow reading it will run. I've seen this many times with these engines and don't have answer except for maybe air in the line. I don't have this issue with the RV7 because the pressure reading is taken at the outlet of the fuel pump instead of the flow divider. I've had two pump failures, about 3 years ago in a PA28-140 and several years ago in a PA28R-200, both times on take off. I didn't know about it until I turned off the electric pump. The 140 had about 300 hours on the pump and the Arrow was a fairly new airplane. Just make sure you have a good electric pump. There are AD's on these pumps and life limits on them as well. I don't think you have an issue but it can usually be fixed if you shut off the engine and wait an few minutes then start it up you will get a better reading.
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  #18  
Old 01-29-2018, 08:22 PM
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Walt Walt is offline
 
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Quote:
Originally Posted by hudgin View Post
Check out your Lycoming Engine Operators Manual. Your engine should put out max 35 psi to a minimum -2 psi. That's negative 2 psi. So the issue is not fuel pressure but fuel flow. As long as there is a fuel flow reading it will run. I've seen this many times with these engines and don't have answer except for maybe air in the line. I don't have this issue with the RV7 because the pressure reading is taken at the outlet of the fuel pump instead of the flow divider. I've had two pump failures, about 3 years ago in a PA28-140 and several years ago in a PA28R-200, both times on take off. I didn't know about it until I turned off the electric pump. The 140 had about 300 hours on the pump and the Arrow was a fairly new airplane. Just make sure you have a good electric pump. There are AD's on these pumps and life limits on them as well. I don't think you have an issue but it can usually be fixed if you shut off the engine and wait an few minutes then start it up you will get a better reading.
These are the numbers I see in the manual:

O-360 Series (Except -A1C, -C2B,
-C2D); HO-360-A, -C Series
Inlet to carburetor; Max: 8.0 Desired: 3.0 Min: 0.5

IO-360 Series (Except -B1A),
AIO-360 Series; HIO-360 Series
Inlet to fuel injector Max: 45 Min:14
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  #19  
Old 01-29-2018, 08:52 PM
hudgin hudgin is offline
 
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What edition or dated version are you looking at? The latest hard copy I have is the 8th Edition dated October 2005. I'm pretty sure that is same as the current version but I no longer have access to it as of Nov 2017.
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  #20  
Old 01-29-2018, 09:00 PM
hudgin hudgin is offline
 
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Im looking at the 8th Edition dated Oct 2005 revision Dec 2009. I believe that is the latest revision but I don't have access to that any more as of Nov 2017. I looking at the inlet to the fuel pump not the injector. Some of my previous post should be disregarded. Thanks for the clarification Walt.
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Last edited by hudgin : 01-29-2018 at 09:11 PM. Reason: Im wrong
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