Mechanical Fuel Pump Oddities

Submitted by Anonymous on

Forums: 

From: Kevin Stallard <kevin [at] arilabs.net>
Sender: <marv [at] lancaironline.net>
Subject: Mechanical Fuel Pump Oddities
Date: Mon, 22 Sep 2014 08:59:24 -0400
To: <lml [at] lancaironline.net>

Hi All,



Recently (within the last couple of moths) as I climb past 8,500ft, my fuel pressure becomes unstable. It drops and rises, from 13 to 14 PSI down below 10 and then back up again. This, of course, has a noticeable effect on engine power (it drops and then comes back).



By the time I get to 8500ft, I've already done the big pull and am running LOP. If I turn on the electric fuel pump, and re-lean, everything stabilizes.



If I don't use the electric fuel pump and deal with the drop and surges in power up to say 12,500ft, level off and begin to cruz, the fuel pressure stabilizes to around 11 to 12 psi and the drops and surges in power stop.



It's an IO-550N and tach time is north of 250 hours.



Ideas?



Thanks

Kevin

Mechanical Fuel Pump Oddities

Submitted by Anonymous on

From: Adam Molny <Adam [at] ValidationPartners.com>
Sender: <marv [at] lancaironline.net>
Subject: RE: Mechanical Fuel Pump Oddities
Date: Tue, 23 Sep 2014 08:50:25 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message

Kevin -



I have experienced a similar problem on occasion. It seems to happen after

the fuel in the wing tanks has become heat-soaked from sitting on a hot,

sunny ramp. I believe that the pre-warmed fuel is prone to vaporizing under

suction inside the fuel lines as the ambient pressure drops. Like you, the

problem goes away if I turn on low boost. I have an air-blast shroud going

to the engine-driven fuel pump but not the gascolator. I too can turn off

the boost pump upon reaching cruise altitude, but that might simply be

because the fuel in the tanks has cooled off by that time.



You might want to just wait and see if the problem goes away during the

cooler months. The only other reasonable explanation for fuel pressure

fluctuations would be an air leak somewhere in the system. The engine-driven

pump is a rotary type, so fuel pressure would drop as the vanes wear, but

it's hard to imagine a scenario where that pump would cause the symptoms you

describe.



Adam Molny

Legacy N181AM

300hrs on airframe, 550hrs on IO550-N



-----Original Message-----

From: Kevin Stallard [kevin [at] arilabs.net (mailto:)

]

Sent: Monday, September 22, 2014 8:59 AM

Subject: Mechanical Fuel Pump Oddities



Hi All,



Recently (within the last couple of moths) as I climb past 8,500ft, my fuel

pressure becomes unstable...



Thanks

Kevin

Mechanical Fuel Pump Oddities

Submitted by Anonymous on

From: Kevin Stallard <kevin [at] arilabs.net>
Sender: <marv [at] lancaironline.net>
Subject: RE: [LML] Re: Mechanical Fuel Pump Oddities
Date: Tue, 23 Sep 2014 11:38:47 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message

From emails, the new forum and from the LML it looks like the only reason the fuel pump is stuttering is because there is air in the line.  That air can come from fuel vaporization, a leak in the fuel line or is because the fuel vents are plugged and/or not enough pressurization is occurring from forward flight.



I'll be investigating over the next week or so and lots of practice flights (darn!)  and I'll report back my results.



Thank you all, I appreciate the time you took to respond.



Kevin

Mechanical Fuel Pump Oddities

Submitted by Anonymous on

From: Steve Colwell <mcmess1919 [at] yahoo.com>
Sender: <marv [at] lancaironline.net>
Subject: Mechanical Fuel Pump Oddities
Date: Wed, 24 Sep 2014 07:12:51 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message

Kevin,

 

I had the same problem on a warm day with warm fuel from an above ground tank.  My solution is to leave Low Boost on all the time.  The Dukes pump is not rated for continuous operation but mine is still running at 200+ hours.  Another plus is, if your engine pump fails on takeoff, Low Boost will probably keep the engine running (maybe at reduced power but still running).  I believe Continental recommends Low Boost above 10,000’ so the best explanation could be “they do that”.

 

Steve Colwell  IO-550 Legacy

Mechanical Fuel Pump Oddities

Submitted by Anonymous on

From: Shane Bangerter <Shane [at] rbr3.com>
Sender: <marv [at] lancaironline.net>
Subject: RE: [LML] Mechanical Fuel Pump Oddities
Date: Wed, 24 Sep 2014 13:19:10 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message

I agree with Steve except I leave
the low boost off during taxi and run up but turn it on before the takeoff roll
and leave it on until back on the ground.  My mechanic was told by CJ
Aviation (828 871 0421) who overhauled my fuel  pump,  the pump has
ran continuously in tests for over a 1,000 hours w/o failure.   I also
recommend you purge each tank before start up to remove any air in the lines
which should prevent a loss of fuel to the engine when switching tanks.

 

Shane 

IV-P 420 hrs  

 

From: Lancair Mailing
List [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf Of Steve Colwell

Sent: Wednesday, September 24, 2014 6:13 AM

To: Lancair Mailing List

Subject: [LML] Mechanical Fuel Pump Oddities

 

Kevin,

 

I had the same problem on a warm day with warm fuel from an
above ground tank.  My solution is to leave Low Boost on all the
time.  The Dukes pump is not rated for continuous operation but mine is
still running at 200+ hours.  Another plus is, if your engine pump fails
on takeoff, Low Boost will probably keep the engine running (maybe at reduced
power but still running).  I believe Continental recommends Low Boost
above 10,000’ so the best explanation could be “they do
that”.

 

Steve Colwell  IO-550 Legacy

Mechanical Fuel Pump Oddities

Submitted by Anonymous on

From: Neal George <ngeorge [at] continentalmotors.aero>
Sender: <marv [at] lancaironline.net>
Subject: RE: [LML] Mechanical Fuel Pump Oddities
Date: Wed, 24 Sep 2014 13:21:14 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message

…so the best explanation could be “they do that”.

 

Yeah…elevated fuel temps, high altitude/low atmospheric pressure, increased head differential due to climb attitude,
vent restrictions (bugs and fuel stains), and the engine-driven pump trying to suck fuel uphill thru the restrictions of fittings, valves and twisting hoses & tubes all conspire to lower the system pressure. 
When the system pressure is lower than the vapor pressure of the fuel, it boils.

 

I’ve also seen fuel lines and boost pumps leak air under suction that don’t leak fuel under pressure.

 

When (before) your Dukes pump goes, consider CJ Aviation (
www.cjaviation.com ) for a replacement or overhaul…

 

Neal
 

 

From: Lancair
Mailing List [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf Of Steve Colwell

Sent: Wednesday, September 24, 2014 6:13 AM

To: Lancair Mailing List

Subject: [LML] Mechanical Fuel Pump Oddities

 

Kevin,

 

I had the same problem on a warm day with warm fuel from an above ground tank.  My solution is to leave Low Boost on all the time.  The Dukes pump is not rated for continuous operation but mine is still running at 200+ hours.  Another plus
is, if your engine pump fails on takeoff, Low Boost will probably keep the engine running (maybe at reduced power but still running).  I believe Continental recommends Low Boost above 10,000’ so the best explanation could be “they do that”.

 

Steve Colwell  IO-550 Legacy

Mechanical Fuel Pump Oddities

Submitted by Anonymous on

From: Steve Colwell <mcmess1919 [at] yahoo.com>
Sender: <marv [at] lancaironline.net>
Subject: Mechanical Fuel Pump Oddities
Date: Thu, 25 Sep 2014 10:38:02 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message

Shane,

 

Thanks for the clarification.  I should not have said “leave Low Boost on all the time.”  I don’t use Low Boost until after run up, to verify the engine driven pump is working.  We flew for over 200 hours without Low Boost with no noticeable problem.

 

Steve Colwell

 

I agree with Steve except I leave the low boost off during taxi and run up but turn it on before the takeoff roll and leave it on until back on the ground.  My mechanic was told by CJ Aviation (828 871 0421) who overhauled my fuel  pump,  the pump has ran continuously in tests for over a 1,000 hours w/o failure.   I also recommend you purge each tank before start up to remove any air in the lines which should prevent a loss of fuel to the engine when switching tanks.

 

Shane 

IV-P 420 hrs  

 

From: Lancair Mailing List [lml [at] lancaironline.net (mailto:)

] On Behalf Of Steve Colwell
Sent: Wednesday, September 24, 2014 6:13 AM
To: Lancair Mailing List
Subject: [LML] Mechanical Fuel Pump Oddities

 

Kevin,

 

I had the same problem on a warm day with warm fuel from an above ground tank.  My solution is to leave Low Boost on all the time.  The Dukes pump is not rated for continuous operation but mine is still running at 200+ hours.  Another plus is, if your engine pump fails on takeoff, Low Boost will probably keep the engine running (maybe at reduced power but still running).  I believe Continental recommends Low Boost above 10,000’ so the best explanation could be “they do that”.

 

Steve Colwell  IO-550 Legacy

 

Mechanical Fuel Pump Oddities

Submitted by Anonymous on

From: George Wehrung <gw5 [at] me.com>
Sender: <marv [at] lancaironline.net>
Subject: Re: [LML] Re: Mechanical Fuel Pump Oddities
Date: Mon, 29 Sep 2014 07:15:44 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message
I am watching Bill Ross' webinar and of course it's everything you taught me.

Sent from my iPad

On Sep 24, 2014, at 13:21, Neal George <ngeorge [at] continentalmotors.aero

> wrote:

…so the best explanation could be “they do that”.

 

Yeah…elevated fuel temps, high altitude/low atmospheric pressure, increased head differential due to climb attitude,
vent restrictions (bugs and fuel stains), and the engine-driven pump trying to suck fuel uphill thru the restrictions of fittings, valves and twisting hoses & tubes all conspire to lower the system pressure. 
When the system pressure is lower than the vapor pressure of the fuel, it boils.

 

I’ve also seen fuel lines and boost pumps leak air under suction that don’t leak fuel under pressure.

 

When (before) your Dukes pump goes, consider CJ Aviation (
www.cjaviation.com ) for a replacement or overhaul…

 

Neal
 

 

From: Lancair
Mailing List [lml [at] lancaironline.net (mailto:)

] On Behalf Of Steve Colwell

Sent: Wednesday, September 24, 2014 6:13 AM

To: Lancair Mailing List

Subject: [LML] Mechanical Fuel Pump Oddities

 

Kevin,

 

I had the same problem on a warm day with warm fuel from an above ground tank.  My solution is to leave Low Boost on all the time.  The Dukes pump is not rated for continuous operation but mine is still running at 200+ hours.  Another plus
is, if your engine pump fails on takeoff, Low Boost will probably keep the engine running (maybe at reduced power but still running).  I believe Continental recommends Low Boost above 10,000’ so the best explanation could be “they do that”.

 

Steve Colwell  IO-550 Legacy