general info.

[tom cloud]

I have recently joined your group and have some serious questions.

I am trying to add EFI to an older vehicle, not modify an existing
unit -- though I have considered going and getting a Ford intake,
runners and injectors, and putting them on my 351-W engine. But, I would
still be back to the original problem -- how to control it.

As I have noted in past postings, I purchased an aftermarket EFI
system that proves that one can be quite effective with a minimal
amount of features -- specifically, this system basically only uses
TPS to determine fuel supply.  [It uses RPM to operate the injectors,
with more fuel being allowed for greater RPM.  Large TPS values
are assumed to imply power, so there is an adjustment to control how
much enrichment to add for 2/3 or 3/4 throttle to WOT.  It also senses the
TPS rate-of-change to simulate the carburetor accelerator pump
function, and it senses engine temp. to provide "choke" cold start
enrichment.]  I can say that the unit is very functional and reliable
though I do have to tune it (the controls are potentiometers under
the dash) periodically to compensate for temperature and altitude
changes -- and often I don't know why it needs adjusting.

Now, it seems to me that a simple EFI system would start with a fixed
injector pulse width.  Then increased RPM would give a corresponding
increase in fuel.  RPM and TPS would also (each) give a relative
indication of the expected operating needs of the engine, a "typical"
correlation between the two being empirically determined.  Then
a large disparity between RPM and TPS could assume a need for more
fuel (TPS > RPM) or for less than the "normal" amount.  Engine
temperature could be used to increase the pulse width at lower RPM
for cold operation.

Now comes feedback.  EGO supposedly tells when conditions are
optimum for the most complete burning of the fuel (stoichiometric,
or A/F of 14.7:1).  But, economy is achieved at about 18:1 while
maximum power is found at about 11:1.  From recent discussions in
this group, it appears that the EGO sensor is useless at determining
anything but 14:7 -- is this right?  And even then how, specifically,
is it's output used?  I have an O2 sensor connected to a DPM and use
it to tune my EFI system.  The writings that I have seen say that
its output swings back and forth between a high level and a low one,
with an average of about .5 volt being sought.  My DPM shows no
pulsating.  Can the EGO sensor's output be filtered to average or
integrate the pulses and provide a steady control signal?

Other sensors that I know of are the MAP, BAP and MAF.  I can see how
a reduced manifold pressure would imply an increased need for fuel and
would modify the previous RPM / TPS determined pulse width, but how
does BAP (barometric atmos. press.) modify that, and is it necessary?

Apparently BAP is not needed if MAF is used.  I can see that, with
MAF, one could actually determine the amount of air entering the
engine and therefore more correctly ascertain the amount of fuel to
add.  How hard is it to add?  How could it be added to a TBI system?
Why isn't manifold pressure and throttle position an adequate indication
of air intake volume?  In fact, since MAF sensors seem to be a pain,
it would seem to me that air volume could be determined quite well
from knowing BAP (the available air density), TPS (the size of the
opening the air is trying to get through, and MAP (the amount of
pressure on the opening).

Then there's my question about EGR.  This is not a sensor, but it
has a marked effect on engine operation.  It seems to give a higher
effective octane thereby allowing the timing curve to be more
advanced than without it.  What that means is that anyone monkeying
with the EGR will end up with pinging at rpm under load and a loss
in power.  This is a particularly onerous problem for anyone
trying to increase engine performance with aftermarket products --
specifically intake manifolds or, as in my case, a carburetor-to-
fuel injection upgrade.

I would like to know if anyone has any control algorithms (digital
or analog) to share, as studying what you've discovered will help
me.  I would like to know any correlations between sensor readings
and fuel control and I need sources of engineering specs. on the various
sensors.

That pretty well sums my rather large ignorance of the subject.

Can anyone help?

Thanks
Tom Cloud