The other issue is when you chop the
throttle from a high setting, to idle. This is very strange. Say
the idle is set at 1900 rpm, and I’m running at high throttle. When I
chop the throttle, the rpm goes low, to around 1600 and stays
there. During this time, the MP is 16.0, and the engine is very
rough. It will stay here forever, but if you turn the mixture knob about
90 degrees CCW to lean it out, it smoothes out, the rpm increases to 1900, and
the MP drops to 13.0. If you are at a higher throttle setting, and
decrease throttle more slowly, it will come down to 1900 rpm, 13 MP, and
smooth. It also seems like the engine is jumping back and forth between
the dual map ranges, and I believe this false 16" MP reading at the rough, low
idle is from the dual map. I think I even proved that to myself by
watching the EM-2 screen that shows EC-2 readings. I’ve got some
work to do on this one, but it's just a tuning issue.
Just to chime in, "Me Too!". I have noticed
the same sort of phenomena.
My guess is that it appears that when closing
the throttle very rapidly, you probably end up with an overly rich
intake manifold air/fuel mixture. This may occur because in one
fraction of a second you are opearting at WOT (lots of fuel flow)
and the next down to idle. So the rpm drops down in to the LOW,
LOW range due to the rapid decrease in manifold pressure caused by the rapid
throttle closure and still rapidly pumping rotors. So its down in
the low rpm range with a rich mixture and then since the rpm is so low,
the manifold pressure may well creeep back up to the 16-17" Hg range simple
because there is not enough rpm to keep the manifold pressure
lower. So now the system is seeing higher manifold
pressure. Since the system only really uses the manifold pressure (and
not rpm) in its calculation, the higher manifold pressure convinces itself
that you have opened the throttle a bit (while you actually have
not) and so it dumps in a bit more fuel. This keeps the mixture overly
rich as there is really not as much air coming into the system.
Once you crack the throttle a bit, more air flow leans out the mixture, rpm
increases, manifold pressure actually decrease back to 14-15" Hg and the
system stabilizes.
Recall this is a pressure density system and
not an Airflow system, so it only knows (or cares) about the manifold
pressure (and in the case of the A controller, your inlet air temp) and knows
nothing about your throttle setting or airflow or even rpm except as inferred
by manifold pressure. Rpm is "automatically" taken care of by the fact
the faster the rpm the more often the injectors are triggered per unit time,
but rpm is not a direct computational factor in determining fuel, only
manifold pressure (and air temp in case of controller A)
My 0.02
Ed Anderson.