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Berni,
Your problem sounds a lot like the one I had. I posted this last year....
Steve Colwell Legacy IO-550
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From: "Steve Colwell" <mcmess1919@yahoo.com>
Sender: <marv@lancaironline.net>
Subject: fuel pressures at altitude?
Date: Thu, 12 Aug 2010 08:20:16 -0400
To: lml@lancaironline.net
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Russell,
You may recall I had a fuel problem just prior to OSH this year (see below).
I did some testing, inspection and cleaning before the next flight and got
the opinions of several experts.
My conclusions are warm fuel and higher ambient temps increase the
likelihood of Fuel Vaporization in the system. Higher density altitude is
also a significant factor. I managed to get away with not using the Low
Boost Pump at some high cruising altitudes for a couple of hundred hours. Reasons to use Low Boost:
On Takeoff, if the engine driven pump fails you are covered.
Climbing out, fuel pressure will be stable and allow accurate leaning.
At cruise, density altitude will not have a detrimental effect on fuel
pressure.
At Airventure, I spoke with several Lancair pilots, Continental and a Cirrus
Test Pilot with over 8 years experience, all seemed to think this procedure
is a good idea. If it means buying a Boost Pump sooner rather than later,
I'm OK with that.
Steve Colwell Legacy IO-550
On climb out to 14,500' yesterday I was having trouble leaning to 1300
degrees. The mixture knob was extra sensitive so I favored the rich side.
I had just topped off with 40 gal. from an above ground tank that was
probably around 80 to 85 degrees. Low boost was used from takeoff to about
1500' agl., RPM was reduced to 2500 and leaning began. Normally,
maintaining 1300 degrees on the hottest cyl. in the climb (per The Advanced
Pilot Course) is easy. (On the previous flight to 15,500' for 2.5 hours I noticed it did not lean
normally but I was able to go LOP and it held the fuel flow @ 9.8 gph. No
fuel had been added and temp on the ground was about 70 degrees.)
When we reached 14,500', we accelerated in level off, reduced RPM to 2300
and started to ease the mixture knob back to go Lean of Peak. At 16.5 gal.
per hr., slowly turning the Vernier about 1/8" as normal, fuel flow jumped
to 9 gph. with the engine faltering. I tried this twice before concluding
"this ain't right". I wish I had thought to use Low Boost or to check Fuel
Pressure, but I didn't. We were over the Sierras and headed for the nearest
airport but maintained altitude and finally circled down over Placerville,
CA. I did not mess with the mixture on descent thinking a running engine
was the best option. The control cable, bracket, arm and movement on the mixture are OK. Testing
for leaks, I had the mixture in idle cut off, throttle open full. With Low
Boost for about 20 seconds, no leaks. Steve Colwell 916 505-6099 Legacy IO-550N mostly stock, no ram air or
injector mods., 225 hours tt.
I'm a little confused over your use (or non-use) of the Electric Boost Pump
at altitude?
Try turning it on LO at 5,000 feet, and HI at 10,000. That's SOP for the
turbos. The boost pump is your friend! On hot days, with hot fuel, you may
need the boost pump for an hour or more at altitude.
Sounds to me like simple vaporization.
Best...
John Deakin
Advanced Pilot Seminars
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