Has anyone used the p port slide throttle with Tracy
    Cook's ECU?
              After changing my engine to the P port configuration with
    the slide
              throttle mounted close to the engine the ECU does not work.
         There is no
              good pick up point for the manifold pressure sensor hose.
    The hose
              connected between the engine and slide throttle gets the
    rapidly
              fluctuating impulses and also fills with fuel from the
    injectors.
              Are there any engines running with this ECU and slide throttle
         set up ?

              John Prendergast

              Mark Supinski is trying as we speak. Any day now. We had
    it running
              on the dyno
              but I ran out of dyno money before we got it tuned
    properly. The
              engine would start easily
              and run but the mixture was all over the map..pardon the pun.

              Since then Tracy has changed
              the computer a lot. I suspect the problem may have been
     >>when<<<
              Tracy was sampling the
              intake manifold pressure. He only takes one sample per rev
    so it is
              only a few
              microseconds long. IMHO many samples should be taken and
    averaged.
              The same thing
              might be possible by hooking up the two pressure taps, one
    from
         each
              rotor,
              to a vacuum can to smooth out the pulses. Slide throttles
    don't
         give
              good
              intake manifold pressure signals when they are wide open as
         there is
              little
              pressure loss in the intake system. That is why they make more
         power.
              All of Tracy development has been done with a plenum on
    the end of
              the tubes
              sampling the pressure just after a single throttle body.

              If your vacuum lines are filling with fuel something is wrong
         with where
              they are mounted. We did not have that problem. Here is a
         picture of
              our set up. Can you send some pictures of yours? Where are
    your
              injectors located?

              You can also try the apex oil injector ports in the rotor
    housings
              for a place
              to sample the intake vacuum... if any :)

              Paul Lamar ...No rotor no motor.

         The injectors are located in a similar position as in your pictures
         except the elbows go forward and then down to clear the
    cowling. The
         vacuum pick ups are  located between the slide throttle and
    engine.
         I believe the  compression wave generated is causing the
    problem. The
         vacuum gage shows such a rapid large fluctuation at the low rpm
    range
         that it would destroy the gage in short order and stops
    fluctuating
         after a short period when the hose fills w/ fuel. The ECU T's
    off the
         same hose which of course could not function properly with these
         conditions.

         The Slide throttle plate is so close to the engine that I
    believe the
         pressure wave bounces off the almost closed plate causing the rapid
         fluctuations and the pushing of fuel into the hose.
         With the original configuration the throttle body was farther away
         allowing a larger volume of air to modulate these vacuum and
    compression
         wave pulses and the injectors were located at the engine not
    before the
         vacuum pick up point as it is now.
         John Prendergast

         ----------------------------------------------------------
         I agree with you on the pressure waves.
         Try smaller hoses feeding into a large can located some
    distance away.
         What you are interested in is the average pressure and not the
         instantaneous
         pressure. I am amazed the gage is responding that fast. Is it
    silicone
         fluid filled?

         What size hoses are you using now?
         We used soft silicone hose which is very flexible. A restrictor in
         the hose will
         also work. Drill a small pin sized hole through a piece of
    aluminum
         or plastic rod
         that fits in the hose. You have got to get rid of those pulses
         as no telling what the pressure sensor is reading as it is only
         sampled for a few  millionths of a second.  Only Tracy knows when.

         The first length of the hose could or should be larger
         so capillary action of the fuel will not occur.  If the hoses
         are coming out of the top of the intake tubes the fuel should drain
         back out no problem.

         Does the hose come off the top of the tubes? We did not have
    trouble
         with
         fuel in the hoses as far as I could tell.

         Mark Su, Please check and see if you are getting fuel in your
    hoses.

         Perhaps we can talk Tracy into a mass airflow sensor mounted on the
         input to the plenum. Mass air flow sensors put out a zero to
         five volt signal just like the pressure sensors. However they have
         a long time constant as they basically measure temperature of a hot
         wire
         and that does not respond to rapid changes in air flow. It
    automatically
         averages out the air flow velocity.

         BTW what does your mixture look up table look like? Perhaps you can
         share yours with Mark Su to get him in the ball park
         as your engine is running.



    I have also found fuel in the manifold lines. Not a whole lot, but
    definitely present.  Sounds like I'll have to mount a can of some sort
    upstream of the pressure regulator to absorb the pulses.

    John -- One thing I would check first is to confirm exactly what fuel
    pressure you are running to the injectors.  I discovered that I appear
    to be running 45psi instead of the desired 35psi - so this could be
    causing the flooding problems I am also experiencing.

    Note that I have in fact had the engine running pported with Tracy's
    ECU.  I got it going last summer.  Very tough to get it firing the
    first
    time.  Once I got it to run the first time, I had a much easier time of
    it subsequently.  Makes me wonder if fuel in the manifold lines got
    'sucked out' after the first run & combined with clean spark plugs
    allowed easier starts after the first.  I had quite rough running below
    2850 engine / 1000 prop.  I am now further wondering if some of that
    roughness was due to the pressure pulses being discussed here.

    I'm stalled on further startup attempts until I get my EC2 and EM2 back
    from Tracy - he's updating them to the latest rev so I have all the
    nifty new EC2 diagnostic modes & the auto-programming mode for the EM2.

    Mark (Rocky Mtn High)

Making the computer take multiple samples might be harder than just
doing a little analog signal conditioning on the sensor data.  Multiple
samples burns CPU time - maybe not critical, admittedly.  If the
pressure pulses feeding the sensor can be damped such that there's no
resonant effects in the sensor system (to keep the sensor from ringing),
doing a little signal conditioning should be easy.

How are the sensors wired?  Are they a variable resistance like an oil
pressure?  It might be as simple as adding an appropriately sized
capacitor to make a low pass filter.  Just need to filter out the
frequency content that's near the operating RPM of the engine.


Regards,

Matt-

I think they are integrated with signal conditioning and they put out roughly  zero
to five volts. They are mounted on Tracy's PC board so the PC board
would have to be redesigned to add signal conditioning. Harder to do than
a software fix. If a 1 Mhz 6502 can do simple EFI than any of todays single
chippers have plenty of time left over :)