general info.

[Alexander M. Lichstein]

EFI is used to maintain a desired A/F ratio under all conditions.  This might
mean 12.5:1 under power conditions (WOT, deltaTPS) and 14.7:1 under normal
conditions (TPS <60%, [IDLE])  Since we must estimate the amount of air
entering the engine in order to allow the correct fuel, we need to know how it
sucks it's air.  While higher RPM does imply more fuel... the pulse widths will
be roughly the same.  This is b/c these pulses are working once per engine
event... it's just that these engine events are happening more often.  This is
not entirely true, however, b/c the engine gets more or less efficient at
pumping air at different engine speeds.  This is dependant on the physical
layout of manifold (tuning lengths...) and valvetrain (overlap...).  This is
roughly called VE or volumetric efficiency.  You will have seen a thread about
this early last month.  

		The accelerator pump concept is merely an effect of the above. 
High deltaTPS or WOT will tell us that the driver would like us to go faster
(or, make more power).  We can do that by changing our fuel ratio from 14.7:1
(cruise), to 12.5:1 or the like.  [You mentioned 11:1 which you may find way
past your peak power and *very* inefficient]  
		Anyway, this change alone can acount for the benefits from an
accelerator pump.  However, the more subtle one is the manifold fuel film issue
which is most pronounced in a TBI or wet-flow manifold like yours.  You must
figure out how much of the fuel you inject is actually getting into the
cylinders when you want it.  An analysis of the liquid fuel stickiing to the
walls will tell you that you must overshoot fuel as you switch to 12.5:1, and
then ease up as this "flood" of fuel makes it's way as vapour to the cylinder.

The O2 sensor will only bounce back and forth is the engine is bouncing back
and forth.  In OEM systems, it is designed to do this.  In yours, it may be
doing this from inaccuracy.  However, you would not be able to see it on a DVM. 
As for interpreting O2... I'll leave that to another as I am stilll working out
the bugs on mine.

MAP - higher the MAP (less vacuum) the *MORE* fuel is needed since the air pump
(engine) is trying to suck this air in.  The lower the P1, the lower the P2,
this the lower the mass of air.  MAP sensors are usually set up to measure the
static pressure and ignore the velocity pressure of the incoming air.  By
knowing the diameter of the tube across which it is looking, all that is needed
is the temperature in order to know the mass-flow.  Ambient pressure is
inconsequential... although it might give a way to correlate TPS with MAP more
easily.

BAP - affects the backpressure on the exhaust side.  Since a MAP based system
is estimating how much aire the engine can pull at that level of Manifold
vacuum and it is *Absolute,  the backpressure at the exhaust will affect how
much air is left in the cylinders when it comes around again... again affecting
the mass air to be burned.  

While we're at it, don't forget HUM.


- Z