I remember seeing a video of a dragster
that had problems with fuel supply. The owner used a clear material (plastic of
some sort I guess) to see what the fuel looked like in the line as the dragster
was needing all available. It showed bubbles. You might do something similar
along the fuel line. Use a high fuel pressure clear hose to see if there are
bubbles and where they might be coming from.
Jim
From: Lancair Mailing
List [mailto:lml@lancaironline.net] On Behalf
Of Craig Berland
Sent: Tuesday, May 22, 2012 8:32
AM
To: lml@lancaironline.net
Subject: [LML] 360 still surging
Berni,
I agree with your
diagnosis that fuel vapor is causing your problem.
-
I am surprised that
the fuel pump on low does not solve the problem. It did on my IV-P
yesterday after breakfast in Arizona. After a few minutes the low pump
was not required.
-
The engine mounted
pump does not “suck” fuel very well and any vapor in the line will
cause you grief. The engine mounted pump may be getting worn with time
and a rebuild may help….I know I am using a lot of “mays”.
-
Some ideas from
me…
o
Make sure the low
boost pump is working….turn it on and listen before starting
engine. This is now on my check list. It should help.
o
If the low boost is
running and does not solve the surge problem then turn on the high boost and
use the mixture knob to get the same fuel rate. Lean for best idle.
o
If the engine runs
smooth on high boost….then look for air seeping into the fuel
lines. Look at every joint between the fuel tank(s) and the engine
mounted fuel pump. If no leaks can be found, I would rebuild the engine
mounted pump or even better replace it. Aluminum housings for any kind of positive
displacement pump is problematic. Just one of many issues…. it is
possible the bores in your pump are a little too big for the
impellers…even though they are within print or service tolerance. Heat
and low RPM is the enemy. The impellers are steel and the housing is
aluminum. The coefficient of thermal expansion is greater for
aluminum. The pump’s ability to pump is therefore reduced at low
RPM when it is hot.
-
The one caution I
would hope to communicate. If this issue is something new, it may be the
early warning of an engine pump failure.
Craig Berland
IV-P N7VG
Many of you guys have offered suggestions to help me remedy my ongoing
engine surge challenge. As a reminder...my fuel injected IO360 displays a
very pronounced surge during idle and taxi following a flight and brief
shutdown/restart. The problem never occurs when the engine iis cool.
I have tried suggestions such as ground running the engine at 1700 rpm
for extended periods following a restart in an attempt to get some air moving
through the cowl but that has resulted in limited success. So far my only
remedy is to let the engine sit for a long enough period to let it cool
significantly. If I do, I have zero issues with surging.
I even removed my fuel injector servo and sent it off for overhaul (not
an inexpensive undertaking) as another attempt to remedy my problem. That
idea does not address what I firmly believe to be the problem, heat causing
fuel vapor lock, but I tried it anyway. I reinstalled the servo yesterday
and test flew. The plane performed flawlessly as it always does following
a first start. When I returned home and let it sit for 20 minutes,
restarted and went to taxi, the surge was just as pronounced as ever.
All of my fuel lines are insulated and fire sleeved. The only
exposed lines are the small lines that run up to the spider on the top of the
engine. I do not have any fuel leaks. Turning on my electric fuel pump,
while increasing fuel pressure from 20 to 25 psi, does not remedy the surge issue.
As posted here before I have taken the active and lifted off several
times with this surge issue going on as the surge quits once I apply full
throttle. As several of you have pointed out this is not a safe way to
proceed therefore I am again asking for ideas/suggestions from you guys.
Many years ago in my drag racing days me and several of my friends
would install a cooling can to cool down the fuel and therefore (we believed)
helped us produce more power. We would use a coffee can, insert a coil of
copper fuel line in the can, put this contraption in line (fuel line) fill it
and fill it with ice prior to a run. While this is not a practical long
term solution, is this the kind of thing I should be doing to prove/disprove my
belief that I have a vapor lock issue?
I sincerely appreciate any and all suggestions!