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1. 06:46 AM - Re: Lycoming Engines-List: Re: High fuel pressure warning (gulf)
2. 08:28 AM - Re: Re: High fuel pressure warning (FLYaDIVE)
3. 09:02 AM - Re: High fuel pressure warning (Bubblehead)
Message 1
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| Subject: | Re: RE: Lycoming Engines-List: Re: High fuel pressure |
warning
With regard to the fuel injection pressure - anybody see an advantage from
reading pressure at "spider" versus at the discharge fitting of the
mechanical fuel pump?
Setting up my engine I noticed the AVSTAR spider has a gage port.
-----Original Message-----
From: owner-lycomingengines-list-server@matronics.com
[mailto:owner-lycomingengines-list-server@matronics.com] On Behalf Of
Bubblehead
Sent: Monday, March 20, 2017 1:57 PM
Subject: LycomingEngines-List: Re: High fuel pressure warning
--> <jdalmansr@gmail.com>
Mel, you are correct. Cessna Centurions are an example. I think the
original poster though was talking about a fuel injected RV-6 and Barry
Check 6 was talking about a fuel injected RV-7A with fuel filters in the
wing roots. The two pumps (electric boost and engine driven) draw fuel
through the wing filters and push it through the finger strainer on the fuel
servo.
Actually in the RVs both carburated and fuel injected versions have an
electric plus engine driven fuel pump. In the carburated version the output
pressure of the pumps is much lower than the fuel injected versions.
I have the same setup on my IO-360 powered RV-8.
--------
John
Keller, TX
RV-8 N247TD
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=467475#467475
Message 2
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| Subject: | Re: High fuel pressure warning |
Hi John & Gaggle:
My response is within the body of your email.
> Barry, I am not sure I understand cause and effect on the aluminum lines being
crimped down. Those are presumably on the suction side of the engine driven
pump. How does that cause higher pressure on the discharge side of the pump?
>
> Clogged filters or crimped lines between the tank and pump could make the pump
have to suck harder and maybe cavitate which would cause reduced pressure on
the discharge side of the pump. I can see how obstructions downstream of the
pump could cause high pressure but not an obstruction on the tank side.
>
Barry - John, I would AGREE with you. There was some unusual plumbing
which brought the plumbing between the seats - I do not recall what
the items were at that location, I have never seen that configuration
before, there is some form of check-valve.
After trying and looking at all the basic issues the inspection lead
me to the inline fuel filters. Should they make a difference and HIGH
fuel pressure? NO! But, they did!!! I can't explain it, I just went
step by step inspecting the fuel supply system. This was surely NOT
what should be. It just WAS. And after cutting off the crimped ends
and installing new filters, the high pressure was under control. Hey!
I do not LQQK a gift horse in the mouth. AND, I would surely like a
better explanation.
> Also, how were you able to isolate the problem to the fuzz in the distribution
side?
Barry - This was fairly easy... I saw the fuzz! It was a small gray
flap about the size of 3 pin-heads. Where it was hiding I have know
idea, it was found on cylinder #3 fuel injection line. How it held on
AFTER I cleaned the system on three different occasions with AvGas I
don't know. It became evident when I cleaned it yet again with
Pressurized Brake Cleaner Fluid, spraying down the tube and into a
white cotton T shirt.
>
> I have a lot of experience operating pumps of all kinds including similar positive
displacement pumps. I also have a ME degree and took the requisite fluids
classes. An obstruction downstream of the pump is essentially a "resistor"
and the system due to the servo is a constant flow (current in electrical terms)
system. To overcome a restriction the pump has to put out higher pressure
just as voltage might have to be increased in an electrical circuit to keep current
the same.
Barry - ME TOO, John, I'm an EE & ME and Retired. As I said, I agree
with you. But! If it works, it works!!! All the LOGICAL
explanations did not work. I truly HATE doing Pull & Replace
Mechanics, I could not find the one item that may have caused the
problem. There might have been more than one reason why the pressure
went high, I don't know. My first thought was the Programming of the
monitor was incorrect, maybe it was, I did reprogram the settings, not
just LQQK at them. But, that does not make sense since the values
read correctly and power is always removed from the circuit every time
the plane is shut down. Sort of like when a computer hangs up... Do a
COLD ReBoot. It was very lucky that I did take these steps, as the
ends of the aluminum fuel lines were reduced from 3/8" Dia down to
maybe 3/32" Dia. The owner was VERY impressed how low his fuel flow
was - But was VERY questionable on why his leaning range was so very
small.
Side Note: Engineers are a VERY unusual breed (Yes we are). We all
went to the same classes we all graduated with the same degree but we
ALL will try to reinvent the wheel. After 40 years in the field I
learned one thing: They are not paying me (enough) to reinvent the
wheel and if it ain't broke don't fix it! LOL!!! LMAO!!!
Barry
Message 3
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| Subject: | Re: High fuel pressure warning |
Barry, your response is one of the best ever! I agree with you on not looking
a gift horse in the mouth. Sometimes things just don't make sense but the engineer
in me (and former Navy Nuke too) just keeps trying to find cause and effect.
I have had the same fuzz problem with injectors, which is why I added filters in
the wing roots. I am going to clean my injectors this weekend because I do
see fuel pressure creeping up and I have not cleaned them in a couple of years.
The Conditional Inspection is due in May and I'll clean the filters in the
wing roots plus the finger strainer at that time.
Congrats on your EE, ME and retirement. I love electrical almost as much as mechanical
engineering and could have easily come out a EE. Never had time to go
back and get the EE but did get an MBA at age 56. I am 62 and still having
a lot of fun in my career so no hurry to retire. Maybe at 66.5 but maybe not.
I really appreciate the fact that you are willing to say "I don't know why" and
"I can't explain it." There are things we just don't have enough information
to unlock but some people refuse to have enough humility to admit they might
not have all the answers.
John
--------
John
Keller, TX
RV-8 N247TD
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=467497#467497
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