Sounds like it could be what Paul Bricker described.  I have an ES and I haven't had it happen to me, but a couple other ES guys have had the surging at altitude, especially when there are high ambient temperatures on the ground.  Some of the IV and ESs have 3/8" fuel lines, the old fuel selector, lots of 90 degree fittings in the fuel lines, electric fuel pump mounted in the copilot foot well fuselage side wall.  Those aircraft seem to be more susceptible to vapor lock.

 

If you've flown the plane for years without a problem, I'd be leaning towards some restriction or leak instead of a fuel system design or installation issue.

 

The leak may be very difficult to find like Scott Keighan described a few posts ago. An RV guy at my home airport went through the same process you did, new fuel pump, etc.  It ended up being a tiny leak in a fuel line fitting that allowed some air to be sucked into the fuel system.  Following that thought, the leak is likely between your electric pump and your engine driven pump.  With the boost pump off, that section of the fuel system is sucking fuel (low pressure, negative pressure).  With the boost pump on, you pressurize that section of the fuel system and keep air from getting sucked into the fuel line (high pressure, positive pressure).  The leak may be small enough that it won't pass fuel out but will let air in.

 

Mike Easley

Colorado Springs

 

 

 

Berni,
What altitude were you flying at when the surging occurred? It was
standard procedure in my ES (w/ NA IO-550N) to turn on low boost above
10000' to avoid this problem.

Paul Bricker

On 5/15/11 5:04 AM, "Berni" <bbreen@cableone.net> wrote:

>I have been trying to chase down the cause of a fuel issue in my normally
>aspirated Lancair IV engine.  During a cross country flight my fuel flow
>indicator began to show fluctuations which I mistakenly believed to be
>false readings.  Shortly thereafter during the same flight the engine
>began surging, slightly at first but increasingly worse in short time.
>So much so that I began to plan for an emergency landing as I was looking
>to find the cause and to introduce a remedy.  I turned on my electric
>(back up) fuel pump and the engine immediately began to run strong and
>the fluctuation readings stabilized.
>
>After gaining altitude I turned off the electric pump and the unstable
>fuel flow readings as well as the engine surge returned.
>
>My initial take was that my problem was caused by a failing engine driven
>fuel pump.  Even with that belief (once back on the ground) I checked as
>much of the fuel system as possible looking for potential restrictions.
>I looked at and cleaned the screens at the wing root connections as well
>as the inlet on the GAMI injectors.  I found no restrictions so I removed
>and exchanged my engine driven pump for a rebuilt unit.
>
>After installing the rebuilt pump the engine tested fine on the ground
>and fine in the air on a subsequent cross country trip.  Approximately
>2.1 hours of flying time later the exact same symptoms returned...erratic
>fuel flow readings followed closely by engine surge.
>
>I am now at a loss as to what I should now look for.  Could my problem be
>due to air somehow being introduced into my fuel flow?  Should I be
>looking at my fuel selector as a possible culprit?  If so how would I
>test that possibility?
>
>Any and all suggestions would be most appreciated.
>
>Sent from my iPad
>Berni Breen
>Bbreen@cableone.net
>--
>For archives and unsub
>http://mail.lancaironline.net:81/lists/lml/List.html



--
For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html