On 07/31/2012 10:57 PM, Frans Veldman wrote:
> I will check the system thoroughly and see if I can find any abnormalities.
An update about this problem.
(For those who didn't follow the conversation; it is about a sudden fuel
pressure drop on a Rotax 914 when applying take off power).
1) The waste gate appears to function normally. It is not binding, it
cycles normally when applying power to the TCU.
2) The fuel flow exceeds 120 liters per hour. So it has nothing to do
with the fuel filters or fuel pumps.
After confirming this, I changed my focus on the fuel pressure
regulator. I disconnected the airbox pressure connector and put a small
hose and syringe on it. With the syringe I could imitate a rising
pressure in the airbox (like the turbo spooling up during TO power).
What I found was this:
1) When I increase the reference pressure, I hear the fuel pump
labouring for a short while, while it has to cope with the higher back
pressure.
2) Whatever pressure I apply to the reference port, it quickly
disappears. There is no external leak according to a "soap" test. The
only possibility is that the air escapes via the fuel return line. (I
did check the syringe and the hoses, this is not where the pressure
escapes). I think that the fuel pressur regulator should not bleed away
the reference pressure.
3) When the reference pressure increases, the fuel pressure lags behind.
It comes up after a short while. It looks like is not a fuel pump
problem, it is the regulator that responds slowly.
4) If I pull the syringe (instead of pushing), there is not so much lag.
It also looks like the fuel pressure regulator holds an underpressur
better than an overpressure. This could mean there is a pinhole leak in
the diaphragm, it lets air more easily out than fuel in.
My conclusion is that the fuel pressure regulator is faulty, binding
and/or internally leaking. Any comments about this?
Should I replace the diaphragm or the whole regulator?
Thanks,
Frans
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