> First of all...thanks to everyone that has tried to help me with my engine
> surge (fuel related) problem on my normally aspirated Lancair IV.  I have
> throughly checked and tested everything suggested so far.  There are no tank
> vent issues and a vacuum test of the entire system from the engine driven fuel
> pump back to the tanks proved there is no air getting into the system.  I even
> replaced the o rings on the inlet and outlet sides of the electric fuel pump
> just to be sure.  Unfortunately my test flight this morning confirmed that the
> issue still remains.
>
> This is what happened.  On a 50 mile cross country where I took off and
> climbed to 7,500 I experienced zero issues.  I landed took on some fuel and
> took off for home.  I climbed to 7,500 again and saw that the fuel flow and
> fuel pressure gauges were fluctuating.  Since this occurrence preferred my
> engine surge problem in the past I knew it was coming and it did.  The engine
> began surging and continued to do so until I turned on the electric ( back up)
> fuel pump.  The engine and gauge readings stabilized immediately.
>
> So this is where I am...I know I do not have any vacuum (air) leaks from the
> tanks through to the engine driven pump, nor do I have any restrictions in the
> fuel lines or fuel tank vents.  I have replaced my engine driven pump.  All
> symptoms remain.
>
> Question...if I am at cruise settings and leaned out reading 16GPH on the fuel
> flow and 10PSI on the fuel pressure should this readings rise when I turn the
> electric fuel pump on?  My GPH goes from 16 to 21 and my fuel pressure goes
> from 10 to 15 or higher.

Berni,

I see fuel pressure fluctuations in my LNC2 after a short fuel stop followed
by a long climb in warm weather. We have talked about this on the LML in the
past for the LNC2 model. As the fuel lines, and everything else under the
cowling, gets heat-soaked during the short stop, vapor bubbles start to form
in the lines and cause the fuel pressure to fluctuate. Turning the pump on,
stabilizes the pressure.

If I climb from a cold start to 15,500ft, for example, I have no problem. My
cooling is fine, so I have no climb restrictions. If I make a short flight
to get fuel, with only a quick stop, and then climb to 15,500, I get the
pressure fluctuations, in warm weather. They are never bad enough to cause
surging, but the pressure will drop from 25psi to around 11-14 psi, and
surge back and forth (if I leave the electric pump off). Once I level off,
and the area at the back of the cowling begins to cool from the climb, and
the heat soaking from the fuel stop, the pressure fluctuations begin to
subside. After 10-12 minutes, they are gone. I have insulated the fuel
lines, which helped, but it still happens. Maybe your problem is something
similar.

Mike Reinath
LNC2 at 1067 hrs
San Jose, CA