Subject:
[FlyRotary] Re: [FlyRotary]
Dave,
It sounds like you have a lean surge region. Engine will drop down in rpm
to
where the fuel Map provides ample fuel, the engine produces more power
and
starts to accelerate and at some higher rpm enters a region of
insufficient
fuel delivery where the engine can not maintain that rpm and
starts
to decrease. As the engine drops in rpm it again encounters a region
where
sufficient fuel exists and starts to accelerate again, repeats, etc.
OK, this I understand.
Here
is what I believe is happening. In my case, When the engine is both
low
in rpm and low in manifold pressure (15" or below) the idle is fine.
However,
if I lower the engine rpm even more the manifold pressure actually
starts
to increase (may go over 17").
This I don’t understand.
Tracy's
EC2 actually computes the
fuel
injector pulse duration based on manifold pressure sensed (RPM simply
determines
the rate that the injectors are triggered). So as the engine
rpm
is lowered (it should require less fuel). But, past a certain point
lowering
the rpm causes the manifold pressure to start to increase (engine
speed
is simply not sufficient to maintain the lower manifold pressure)
Normally one would
decrease rpm by further lowering the MAP by further closing of the throttle
plate. Do you mean you reduce the rpm by some means other than decreasing
manifold pressure? Like changing the mixture?
when
that
happens the EC2 senses that INCREASE in manifold pressure and treats
the
increase as a demand for more fuel when in reality the new lower rpm
requires
proportionately less fuel. This gives you an overly rich condition
so
you reduce the air/fuel ratio with you mixture knob. When you do that
you
reduce the mixture sufficiently from the overly rich side to cause the
engine
to increase in rpm this may cause the manifold pressure to actually
decrease
(goes say from 17" to 15" as the rpm picks up a bit). Manifold
pressure
decrease causes less fuel to be injected causing a lean region and
engine
dies back in rpm, etc..
After sufficient
leaning, I was able to get my engine to run OK on the dyno at low rpm with the
550cc/min injectors (primary in the housing); with fixed 40psi fuel pressure.
The issue I couldn’t resolve was the ‘overshoot’ – decelerating
from a higher rpm and MAP going to a level below where I could make an adjustment
– resulting in the engine dying. The EM-2 is going to allow me to
resolve that; right?