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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.
If I recall correctly you are using the 550 cc/min turbo II injectors. I
attempted to use those on two occasions and reverted to the 460 cc/min
principally because I could not get as smooth an idle as I prefer.
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"). 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) 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..
Dave, If you have not use MODE 3 to try and lower the over all fuel flow you
might try playing with that. Tracy has some details in his EC2 installation
instructions on page 12 of my instructions. Basically you set the mixture
to where it is running slightly rich and then with the program knob in the
0900 O'clock position and MODE 3 selected, you push the program button. You
may need to press it more than once. But, read Tracy's section on MODE 3
programming. dated 08-15-01
The only other thing I can think of that could be causing it is a leaking
injector, however, since you get the same results with either primary and
secondaries on at low rpm, I would discount having two leaky injectors (one
in primary one in secondary).
I personally would not consider lower the fuel pressure unless the MODE 3
adjustment provided no results. My fuel pressure normally runs between 40
and 43 psi.
Good luck, Fellow.
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
From: <daveleonard@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, May 05, 2004 2:51 PM
Subject: [FlyRotary]
Hi all, I spent a couple of hours the other day gathering clues to my rough
running problems. First the facts, then my theories. I'm looking for any
input.
Description of the problem: The problem is really more of a surging rather
than rough running. At less than about 2200 RPM the engine will begin to
surge. It gets worse the more I lower the RPM. Each time I make a change
to the throttle setting I adjust the manual mixture knob to find the leanest
point where the engine does not surge. I have Tracy's standard mixture
monitor.
Each cycle of the surging takes a little over 1 sec. RPM surges buy 300-400
RPM. Manifold pressure fluctuates by 2-3 inches, and the mixture monitor
fluctuates the full range of its scale.
At this point I can manually increase the mixture up to the first red bar.
This is over rich and the engine runs a little rough and the RPM drops a
couple of hundred. It will smoke a little more, but at least the surging
stops. If I lean down into the amber area the surging starts again. The
surging gets very bad if I lean down into the middle of the scale. This is
what happens around 2000 RPM and 15in MAP.
If I further close the throttle, the surging is similar but to a great
scale. In order to stop the surging I have to increase the mixture beyond
the top of the scale. Here it will be running rough from an overly rich
condition but still surging a little too. Down around 1000 RPM it is still
surging but so rich it will barely run. Beyond that point, either the
richness kills the engine, or the surging kills the engine.
Assorted clues: Several additional clues may shed some light on the
situation. Mostly centering around the Fuel Pump. I have noticed that if
the engine is running rough from being too rich (wont run leaner because of
the surging) and I turn the engine off (by shutting off the fuel pump) the
will run perfectly smoothly for several seconds before it stops. In other
words, as the fuel pressure drops below 10 psi the mixture is lean enough
for the engine to run well and it purrs for a couple of seconds without
surging until the fuel pressure reaches zero.
In an attempt to track this down more I ran a couple of experiments. I
normally run 45 psi of fuel pressure. I have the TWM adjustable with
manifold compensation. First I turned down the fuel pressure to 40 ( as low
as mine goes) and possibly saw a slight improvement. Then I turned up the
fuel pressure to 55psi and the surging definitely got worse. The cycle time
was faster, it was harder to get it to go away by enriching and the problem
continued up to about 2800 RPM.
So it wants a lower fuel pressure. But why? More experiments:
1. Did my best to match the mixture between the two rotors, but with the
turbo I only have a single common EGT. I noticed a slight improvement.
2. Unplugged the turbo air inlet (engine now running n.a.) - no change.
3. Disconnected the MAP line from the fuel pressure regulator - no change.
4. Had my EGR passages welded closed (in case they were leaking) - no
change.
5. Tried assorted arrangements of where to sample MAP - no change.
6. Run engine on either the primary injectors (stock turbo in the engine
block) or the 52 lb secondaries in the Throttle body - no change.
7. Run on leading or trailing coils. - no change.
8. adjust timing with light - no change.
Other findings. I had previously that turning off my alternator caused my
engine to stop. I turns out that turning off the alternator just makes the
mixture leaner. The effect is smaller if running on only one set of coils,
and exaggerated if there is a high amp load. But this situation is always
fixed simply by enriching the mixture (about 110 deg turn of the knob). The
buss voltage
Summary: So it seems that installation is particularly sensitive to changes
in fuel pressure. My next step will probably be to buy a lower pressure
fuel regulator. The thought is that maybe running 35 PSI will stabilize
everything (i.e. maybe with only having to hold 35 psi the pump will no be
as affected by changes in fuel flow or system voltage. I will have my
injectors checked and cleaned although I don't imagine that will help.
Any other thoughts?
Thanks ahead of time for any input I may get.
Dave Leonard
>> Homepage: http://www.flyrotary.com/
>> Archive: http://lancaironline.net/lists/flyrotary/List.html
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