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
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