I used to think a pressure sensor driven EFI system required an air
temperature input and a computer to work.  That ruled out the pressure
sensor in my feeble mind for a simple and cheap 555 system.  I thought I
needed a MAF sensor.  Then I found out that mass air flow sensors are
not linear.  Then I thought well I would use a cheap computer to
linearize the mass air flow sensor.

I have since changed my mind. All one need do to start the engine is set
the leaning knob commensurate with the out side air temperature.  Cold
day set it richer.  That simplified the system greatly and we can use an
ordinary
555 system as a manifold pressure sensor puts out a linear signal unlike
a mass air flow sensor.  TLC555 are linear devices.  PW hence fuel
injected is directly proportional to sensor voltage.  I now agree with
Tracy Crook almost.

The benefit is a much cheaper system with no need to buy a $80 or $100
mass air flow sensor and install it on the plenum.  If it is not there
it weighs nothing and is absolutely reliable.  The other benefit is
pressure sensors cost less than $10 each so we can use two....  one for
each rotor.  A little redundancy for back up use.

Since the manifold pressure is linear we don't need the super 555
microcomputer chip and a $1 analog TCL555 will work just fine as is.

I have got to get something working soon. As I will have some engines to
test soon.


Paul Lamar



Hi Paul

Fuel injection that thinks like a "SU"

Electronic Constant Depression Injection "ECDI"

Brilliant!!!!!!

Err....Don't those LM335 temperature sensors give a linear output to set
the basic enrichment.

Plus the leaning pot for finer adjustment.

Not a pesckiy programying head scratchy brain numbing computa in sight.

Where's the kit???????????????
Where do I GET SOME???????????????

Clive

Temperature compensation requires a computer. One must convert the
output, linear or otherwise, to a digital quantity.  I have decided not
to use a computer. Too costly and over kill for an aircraft engine. The
$1 TLC555 chip does 90% of what a computer does in an aircraft EFI
system. It takes in an analog voltage from a $10 intake manifold
pressure sensor or MAF and outputs a pulse width to an injector. The
cost is less than $20 per injector.

Recently we discovered one of the severe problems tuning Tracy's
manifold pressure driven EFI system. Those problems soured me initially
on pressure driven EFI systems.
Apparently the pressure sensor was seeing a lot of turbulence inside the
intake manifold. The character and intensity of the turbulence varied as
a function of RPM and throttle opening. People had to set values in the
mixture table for every combination of throttle opening and RPM. You
should not have to do that.  IMHO this was causing all sorts of tuning
problems. We discovered this with a high speed (1000 samples per second)
pressure data acquisition system.  We discovered that measureing the
pressure in the intake chamber of the engine using the apex seal oil
injector hole was ten times more stable than measuring it in the intake
manifold. See the data plots.

So that is what I am going to use to drive the 555.

Paul Lamar


Outstanding Paul.
Michael Decker