Today
while flying my first take off was normal. The second take off my fuel
flow
on
takeoff went up to 19.0gph then back down to 12.2 after rotation then
slowly
went back to normal. Cruised around ok for 15 min then back to the
airport
for
a couple of circuits. No electric boost pump except I turned it on for
landing.
Next
take off the same thing but max Flow on take off was 18.5gph for half a
second then
it
went back down to 14.5. Turn on the electric boost and within 2 seconds
its back up to 20.5gph.
Landed
and on a back track for another circuit the engine stalled. Restarted
right away with
no
issues. Next circuit same issue. Up to 18.0gph then down to 15.0
while rolling down
the
runway, hit the boost pump and within 2 seconds all is well. On downwind
switch the
boost
pump off and the fuel flow stays in normal ranges. Take off left or right
tank, same issue.
Fuel
25 gal in each tank.
Fuel
pressure stays normal the whole time. I checked for water in the
tanks and gascolator.
I
checked underneath the cowl for anything out of place.
Engine
fuel pump rebuild required?? What do you think??
Any
advise would be appreciated.
Scott,
This sounds like a classic case of fuel vaporization to me. The
fact that the electric boost pump helps tends to support this hypothesis as the
pump adds pressure, causing the fuel to re-liquify (stop boiling) in the engine
compartment.
Fuel vaporization is caused by the hot engine—and is exacerbated
by low air flow on the ground, but it could be aided by lines being too close
to hot exhaust air/pipes, or not wrapped/insulated. I’d recommend a
second set of eyes to look over the fuel line routing and insulation in the
engine compartment. My IV-P has a shroud around the gascolator that receives cool
air through a SCAT tube from the top front of the engine for just this purpose.
Ditto for the shroud around the engine-driven fuel pump/controller.
This is not a trivial, nor an uncommon issue in the summer, but
needs to be looked at carefully. Although the problem is usually corrected as
you accelerate and draw in cooler air on takeoff, it can, and has caused loss
of power at this critical time…a true attention getter, if not accident.
This one is worth spending some time on IMHO, but look at these
things before you tear into the fuel pump, etc.
Bob