Posted for bob mackey <n103md@yahoo.com>:

  Jeff:
  If the engine (including injectors, fuel servo, etc)
  only works when fed fuel of just the right pressure, then
  the airframe's fuel system must supply fuel of just that
  pressure.

  To my way of looking at the system... The IO-550/Lancair system
  as describe here has both an engine problem and a fuel delivery
  problem.

  As an example of fuel-system responsibility consider the
  cases in which stagnant hot fuel and vaporizes
  causing vapor lock ar least insufficient fuel delivery.
  The simple solution to that problem is to pump the fuel
  from the tank to a pressure regulator near the injector servo,
  and return the regulator excess to the tank. It works in your
  car, even with much more volatile fuel.

  As an example of engine fuel injection problems, I submit
  that if changes in the fuel pressure delivered to the injector
  servo cause the engine to run unacceptably rich or lean,
  then the injector servo is not doing its job. I don't have
  a Continental IO-550, and I am not familiar with its operation
  other than what I've read here. What I have read here makes me
  think that the fuel injection is overly sensitive to fuel
  pressure variation.

  For comparison, the carbureted Lycoming O-320 in my LNC2
  changes fuel flow by about 4% (13gph max vs 12.5).
  Not enough for a noticeable change when ROP,
  At 12500 ft, I cruise LOP at about 6.5 gph, Again, changing
  the fuel pressure by switching the pump on has little effect.
  If I remember correctly, the fuel pressure varies from about
  20 to 35 psi (or whatever units the EI FP-5L reports).
  The system works because the carburetor's bowl, float, and needle
  regulate out the pressure changes. I did just replace a leaking
  needle/seat, so the 4% variation might have gone away.

  For further comparison, the engine in my Toyota MR2 hasn't run
  noticeabley rich or lean for the last 175,000 miles.
  There has been no service of the fuel system for 17 years.


"""
  Are you certain it is an engine issue and not a fuel system issue?
  
  Regards,

  Jeff Edwards
  LIVP N619SJ
"""