Accel enrichment

[Shannen Durphey]

Tony Bryant wrote:

> Why is accel enirchment (== throttle pump) needed?
>
> I'm talking about the momentary increase in required injector
> duration when the throttle is quickly opened, as opposed to constant
> running at WOT at that RPM.
>
> For example a transition between from 15" vac to 0" (WOT) at say 2000
> RPM.
>
> I'm trying to optimize this part of my algorithm, and I need to
> have some sort of understanding of what I'm trying to fix.
>
> What is going on in terms of MAP, air flow velocity, pressure,
> fuel vaporisation and VE?
>
> What algorithm are in use, and what do they depend on?
>
> Any help greatly appreciated.

  Are you talking TBI or TPI? In a wet flow induction system, if you
allow the mixture to get too lean while it's in the intake, it
backfires.  And on port fi, the mixture in the cylinder will get
extremely lean and can pop out the intake valve.  Same end result.  From
what I know, carburetted induction systems which do not use an
accelerator pump run a richer mixture and/or (relatively)retarded spark
timing and/or slower opening throttle plates (vacuum controlled) to
prevent leaning out the mixture.

MAP is manifold absolute pressure, so it reads the pressure in the intake
as a relation to atmospheric.  It acts like a very sensitive vacuum gauge
and records a drop in vacuum (really an increase in pressure) as
atmospheric air rushes into the manifold.

HTH
Shannen