Berni,
I
agree with your diagnosis that fuel vapor is causing your
problem.
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<!--[endif]-->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.
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<!--[endif]-->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”.
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<!--[endif]-->Some
ideas from me…
<!--[if !supportLists]-->o
<!--[endif]-->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.
<!--[if !supportLists]-->o
<!--[endif]-->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.
<!--[if !supportLists]-->o
<!--[endif]-->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.
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<!--[endif]-->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!