I'm going to ground my airplane until I get to the bottom of this. I can
tune it on the ground and it will run just fine all the way from idle to
full throttle. I get about 5300 rpm at full throttle at 29 in hg. MP. I
have 12 hours in the air so far but can't get past this issue. Other
than this, the plane is an absolute joy.

When  I get off the ground, when I go through around 5400 RPM, I start
to get stumbling and engine roughness. At this RPM I am about 18 inches
MP. Just below this point, I am making about 50% power and the engine
will run smoothly.

I went to another airport and had a lot of roughness on takeoff, but I
am used to it and so continued on my way to my home airport. When I got
back I found out that someone at the other airport wanted to report me
to FSDO because he thought my engine was going to blow up, but he didn't
get my tail number.

So, I thought I had it sorted out before I flew today, but it's back to
the drawing board. I've tried both leaning and enriching the mixture at
all throttle settings, but to no avail. At and above 5400 rpm I start
getting all sorts of roughness so I think that it has to be an ignition
issue. My injector wiring is separated from my coil wiring, but could I
be getting inductance between the different coil wiring?

I have a 93 13 BREW normally aspirated, 2.85 RWS redrive, EM2, EC2, 88x
74 CAtto Prop. This is getting to be really frustrating. It's got to be
something simple that I'm overlooking. I don't know anyone with an
ocilliscope, and have never used one.

Brian Trubee


Does the intake system still look like this?  If so remove
the large right angle pipe before the throttle body and fly it again.
Don't worry about where it is getting the intake air. There are probably enough
leaks in the cowling to supply enough air for the engine.

That pipe is resonating somewhere in your RPM range. Probably around 5500 RPM. I
don't know for sure if that is the problem but it is worth a quick try.

Is there an opening in the cowl on the bottom for the intake air?
If so take some pictures of it.

---------------------------------------------------------------------

I am looking for a different response Brian. Without the pipe
it still may run rough so it will need to be re tuned for that
configuration. In principle it is a good idea to keep the length
of the intake tract up to the throttle body as sort as possible.
That means an air intake some where near the throttle body
on top of the cowl.

I am sorry but every time I hear about these kinds of problems I get angry.
If I put on my programmers hat I know that Tracy's EM2 engine monitor
could be ten times better if only he added a USB port and sent all the
data to a net book, tablet or God forbid even a recent cell phone.

Back in the
early days of the personal computers and the Apple II we immediately
discovered that less than 80 characters per line and 25 lines was not
a viable user interface. The EM2 screen is a far cry from this minimum
required user interface. Now a days we can have 100 characters and 100
lines on a high resolution color net book or tablet screen.

Here is the problem. You can not see a complete map of the mixture as
a function of RPM and intake manifold pressure on the EM2 screen.
This makes it far more difficult to trouble shoot these intake manifold problems.

As an illustration of what I am talking about here are a couple of the
possible tuning screens on a Megasquirt system. The Megasquirt has an
USB port to talk to a PC, tablet, net book, notebook, etc., etc.

I am not advocating Megasquirt as it is not optimized for aircraft use
and it has a steep implementation and learning curve despite its open
software and hardware. I am advocating a much higher res EM2 display
screen and or a USB interface.

Tracy's computer already has one or more serial interfaces that
can be converted to USB ports. Here are some examples of cheap hardware
that can do it. The PC software can be programmed in something
simple like Visual Basic.

It would be way less of a tuning problem if everybody built P-ports.
That is the closest thing we have to a standard intake manifold
configuration over a wide range of 13B engines starting in 1973 up
to the current RX8 engine.

Unfortunately there are a lot of engines still out there with
all sorts of variations on side ports not to mention some with turbo's.

The side port engine can be a nightmare if there are two or more resonant
intake systems in series. The stock RX8 intake manifold is a classic example.

Paul Lamar



Why not a Megasquirt optimized for airplane use?  I was thinking about it anyway...

Sincerely,
David Goings

They have added so many bells and whistles to Megasquirt it is hard to sort
out what will work for an aircraft.

If I were doing Megasquirt I would go for the earliest simplest system.
If you do get involved keep us informed on what works or does not work.

Paul Lamar