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