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Date: Tue, 10 Apr 2012 16:07:22 -0400
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From: Tom McNerney <dudewanarace@yahoo.com>
Reply-To: Tom McNerney <dudewanarace@yahoo.com>
Subject: RE: [LML] Engine "surge" issue
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I would offer this advice..=0A=A0=0AThe fuel may be boiling in other places=
, other than the injector lines..=0A=A0=0AMy airplane was converted from ca=
rbureted to fuel injected some time ago.=A0 A dukes boost pump was added on=
 the engine side of the firewall.=0A=A0=0AAfter shutdown and it heat soaked=
 for a bit, a bubble would form in the boost pump.=A0 When=A0the pump was t=
urned on, it would essentially run dry and not move any fuel.=A0 (Verified =
by fuel flow and pressure, plus you could hear it zing up to rpm)=A0 So, th=
e quick fix was to crank the engine and the mechanical pump would pull the =
bubble past the boost pump, then leading to a normal hot start.=A0 But, onc=
e started fuel pressure would be very erratic and often low, combined with =
engine stumble.=A0 It took a few minutes of running to clear the system of =
the air and normal fuel pressure would return. 25psi+=0A=A0=0AThis boost pu=
mp was in an "airbox" with cooling air provided by a blast tube off the rea=
r baffle.=A0 In flight that theory worked, but not when parked.=A0 I think =
the box itself was the main cause of the heat soak problem, along with the =
orientation of the pump/lines.=0A=A0=0ASolution:=0AMoved pump/lines to a po=
int where a bubble would migrate uphill through the boost pump to the mecha=
nical pump. (Then you could always push the bubble with the electrc=A0pump,=
 if you got one)=A0 Also removed boost pump "airbox" and only use a cool ai=
r blast tube for cooling.=A0 Let the heat escape in to the cowl when parked=
.=A0 Haven't tested this yet, as still finished up V2.0 firewall forward st=
uff.. :)=0A=A0=0AMoral of the story: notice location of all fuel system par=
ts and relative heat sources, moving and not moving.=0A=A0=0A=A0Tom McNerne=
y=0Awww.N54SG.com (hopefully lots of updates soon)
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<html><body><div style=3D"color:#000; background-color:#fff; font-family:ti=
mes new roman, new york, times, serif;font-size:12pt"><div>I would offer th=
is advice..</div><div>&nbsp;</div><div>The fuel may be boiling in other pla=
ces, other than the injector lines..</div><div>&nbsp;</div><div>My airplane=
 was converted from <span id=3D"misspell-0"><span>carbureted</span></span> =
to fuel injected some time ago.&nbsp; A dukes boost pump was added on the e=
ngine side of the firewall.</div><div>&nbsp;</div><div>After shutdown and i=
t heat soaked for a bit, a bubble would form in the boost pump.&nbsp; When&=
nbsp;the pump was turned on, it would <span id=3D"misspell-1"><span>essenti=
ally</span></span> run dry and not move any fuel.&nbsp; (Verified by fuel f=
low and pressure, plus you could hear it zing up to rpm)&nbsp; So, the quic=
k fix was to crank the engine and the mechanical pump would pull the bubble=
 past the boost pump, then leading to a normal hot start.&nbsp; But, once
 started fuel pressure would be very erratic and often low, combined with e=
ngine stumble.&nbsp; It took a few minutes of running to clear the system o=
f the air and normal fuel pressure would return. 25psi+</div><div>&nbsp;</d=
iv><div>This boost pump was in an "<span id=3D"misspell-2" class=3D"mark">a=
irbox</span>" with cooling air provided by a blast tube off the rear baffle=
.&nbsp; In flight that theory worked, but not when parked.&nbsp; I think th=
e box itself was the main cause of the heat soak problem, along with the or=
ientation of the pump/lines.</div><div>&nbsp;</div><div>Solution:</div><div=
>Moved pump/lines to a point where a bubble would migrate uphill through th=
e boost pump to the mechanical pump. (Then you could always push the bubble=
 with the <span id=3D"misspell-3">electrc&nbsp;</span>pump, if you got one)=
&nbsp; Also removed boost pump "<span id=3D"misspell-4" class=3D"mark">airb=
ox</span>" and only use a cool air blast tube for cooling.&nbsp; Let the he=
at
 escape in to the cowl when parked.&nbsp; Haven't tested this yet, as still=
 finished up V2.0 firewall forward stuff.. :)</div><div>&nbsp;</div><div>Mo=
ral of the story: notice location of all fuel system parts and relative hea=
t sources, moving and not moving.</div><div>&nbsp;</div><div>&nbsp;Tom McNe=
rney</div><div><a href=3D"http://www.N54SG.com">www.N54SG.com</a> (hopefull=
y lots of updates soon)</div></div></body></html>
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