Can anyone offer input as their take on the following data.  It is fuel flow and fuel pressure readings on a normally aspirated Continental IO520 powered Lancair IV.  On a flight today we experienced a very poorly running engine as we gained altitude. 

 

                        Fuel Flow                     Fuel Pressure

On runway       25.57                            15

1000’                24.3                              15

2000’                24.2                              15

3000’                23.0                              13

4000’                22.0                              13

5000’                20.6                              12

6000’                19.0                              11

7000’                18.0                              10

 

At 6,500’ the engine began surging.  When we turned the auxiliary fuel pump on the engine immediately ran fine.  We have now had the engine driven pump overhauled.  We have pulled vacuum through the entire fuel system and we have no leaks.  We replaced 100% of the flexible fuel lines.  Metered and un-metered fuel pressures are reset and fine.  We are at a loss as to what is causing our engine surging problem.

 

Berni