Forwarded from the bounce bin. Message is from
Klaus Dietrich <Klaus.Dietrich@oracle.com
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Alan,
I experienced very similar engine cough/stutter under very similar
conditions. However in my case I believe it is a combination of low fuel
pressure at max continuous power and possibility of vapor lock at high
OAT.
(I have also the return line fitted and also fly with Auto Super
unleaded from the airport pump; TT: 350 hours)
I had such coughs now three times (each lasting only 1-2 sec) in this
summer (never had it in winter) and only at MCP at max. cruise
(5.500rpm) It stopped immediately when I turn on the electric fuel pump
and when retarding the throttle to more normal 5.200 rpm.
As I have a fuel pressure switch installed, I can clearly see how, at
MCP (+ hot engine with oil temp at 110C, my warning light start to go
on and off and has the tendency to stay on permanently if I will stay
prolonged at MCP (for more than 5-10 minutes).
However I have the strong feeling that also under normal condition the
fuel pressure as generated by the mechanical pump is on the low side (at
least on my engine). I will have to verify this by testing, although.
All filters are clean and I can also close the return line with a small
valve and still have the low pressure light coming on (fuel pressure
sensor has also been checked and replaced with no results).
Next I will check my fuel lines for any bends, the electrical pump (new
model installed), my flow meter (ELBA) and last the mechanical pump
(which should last forever according Rotax....)
Will let you know.
All the best
Klaus
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