Hello Paul-

Sent this to Tracy earlier today; thought I would pass it along in case
someone on the list has seen this before...

Had some peculiar behaviors in that latest tuning attempts.  Hopefully
you'll have some suggestions.

Background-

   - 13b, p-ported, with slide throttle design & "tuned" intakes
   - LS1 injectors
   - EC2 with latest p-port firmware
   - EM2
   - 6800 field altitude
   - 55F OAT
   - Known to be under propped (has a 72x72 160hp 2-bladed prop.  Needs a
   72x109 230hp 3-bladed prop)

Symptoms-

If we run the engine with the manifold pressure lines *DISCONNECTED *from
the EC2:

   - Engine starts very easily
   - The engine runs quite smoothly across a pretty wide rpm band after
   tweaking the manual mixture control.
   - Reasonably smooth running as low as 1500rpm engine (526rpm prop!)
   - Very smooth running 3000 - 4800 RPM.
   - Above 4800 rpm we seem to "run out of enrichen" on the manual mixture
   control & the engine stops.
   - MAP table view on the EM2 real-time shows the EC2 using map location
59
   or 91 (MP constant matching atmospheric pressure) depending on high/low
   throttle (as expected)


If we run the engine with the manifold pressure lines *CONNECTED *to the
EC2:

   - Engine noticeably harder to start
   - Engine will not run smoothly at any rpm
   - Significant surging pattern -- rpm increases rapidly, followed by
   engine stumble to low idle rpm, followed by next surge.
   - Engine often stops during the stumble / hard to restart
   - MP pressure varies rapidly based on engine rpm
   - Significant manual mixture changes can help ease the surges somewhat,
   but never enough to get the engine to smooth out enough to let us see if
MAP
   values could be tweaked.


Looking at the MAP table with engine off, it seems like all map cells are at
0 -- as expected.  I did not check all 127 cells, only the top cells (say
100 - 127).

Mark (Rocky Mtn High)

IMHO you need
to feed the manifold pressure  from both intake tubes past the slide
throttle
using very small hoses into a beer can and then tap out of the beer can with
one normal size hose going to the pressure sensor in the computer. Hopefully
this will damp the pulsations and average the intake manifold pressure.

Al Gietzen tried this as I recall and it did not seem
to change anything. I don't know what size hose Al used
but I think very small hose is essential. On the order of .030
inside diameter or smaller.

Paul Lamar
----------------------
The surging behavior suggests the engine is running way too lean.
Check the basic pulse width - adjusts with mode 3.
Where are you picking up MAP?  Paul's suggestion on damping the
Pulses is a good one.  My pickup points are about 8" upstream
From the ports on my 20B. I sense MAP on all three connected together;
And did find that it idled better with some pulse damping.  Didn't matter
much above about 1600 rpm.

I put a metal fuel filter, about 2 1/2" dia., in the line, and about a
.040", 1/2" long orifice between the filter and the EC2.  It helped to smooth
things out, although one reason was to smooth out rapid pulsation
I noted in the fuel pressure from the MAP reference pressure regulator
T'd off the same line.

You may want to chat with Tracy on the matter.

Al Gietzen

Interesting Al. I forgot about the fuel pressure regulator.
That could be part of the problem. Thanks Al.

Perhaps there is a USB data acquisition system out there we can
use to monitor intake manifold pressure with a high speed
sensor and my EeePC or any computer for that matter.
http://www.ni.com/dataacquisition/usb/

I'll have to look into this further. It would be nice to know what
is going on in the intake manifolds.


Paul Lamar