Accel enrichment

[Shannen Durphey]

Ludis Langens wrote:

> Raymond C Drouillard <cosmic.ray at juno.com> wrote:
> > Well... after considerable thought, it's quite simple!  <:)
> >
> > When you suddenly open the throttle, a lot of air suddenly rushes into
> > the manifold.  You need to inject enough fuel for that air.  How much
> > will depend on the vacuum before and after, and the volume of the
> > manifold.
>
> Yes, of course.  But - GM appears to inject even more fuel above and
> beyond what that air should need.  The normal speed-density calculations
> should provide the matching fuel for that air.  However, when the ECM
> sees a sudden opening of the TB, or a sudden increase in MAP, it starts
> asynchronously injecting additional fuel by pulsing the injector(s) at
> 160 Hz.
>
> The normal synchronous injection occurs when there is a reference pulse
> (from the ignition module.)  If the ECM's sensor inputs change before
> the next reference pulse, the ECM can change it's mind as to the
> injector pulse width.
>
> The asynchronous injection happens _right_now_.  The injector pulse
> width is clipped to a duration of less than 1/160th of a second.  If the
> called for duration was longer than this limit, the remainder is saved
> for the next 160 Hz cycle.  Further, this async injection is cumulative
> - as long as the ECM sees a rising TPS or MAP, it will keep adding to
> the pending duration.  And if the TB suddenly snaps closed, any pending
> async fuel will still be injected.
>
> [The above applies to SD applications, but MAF should be similar.]
>
>                unsigned long BinToBCD(unsigned long i) {unsigned long t;
> Ludis Langens     return i ? (t = BinToBCD(i >> 1), (t << 1) + (i & 1) +
> ludis at cruzers.com            (t + 858993459 >> 2 & 572662306) * 3) : 0;}

  Just a thought, some GM SD systems have no intake air temp sensor.  Maybe
xtra fuel makes up for possible sudden drop in air temp?

Shannen