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