Asynchronous injection (and PLD)

[Walter Sherwin]

That's quite interesting.  I wonder the reasoning behind why GM would force
those particular TBI cals into ASYNCH at all times, and yet not others?  I
can understand the need for ASYNCH under certain specific conditions, but,
would have intuitively envisioned SYNCH as having more benefit when the
other mode was not absolutely necessary.  What exactly are AKDX and AKSN
from?  Have you had a chance to run those cals yet?  Or, at least the same
strategy in your cal, as an experiment?  I'd be curious to know.   Maybe the
OE application had either a quirky intake manifold problem to overcome,  or
perhaps was overly sensitive to bank phasing as a result of having merely
the distributor REF signal as a TBI trigger (ie: no cam signal)?
Puzzling.....

Walt.



>
> Walt, your not going to believe this. Yesterday I was looking at a bunch
> of '747 bins researching the different bpw's that the sync & async pulses
> are switched at (along with inj bias val). I found two bins that run in
async
> mode all the time!
>
> akdx & aksn are 4.3l bins that have the sync to async switch point at
> 13 msec. At first I thought it was a mistake in the bin. Then thinking
about
> it realized how it would really work. These bins would run in async mode
> all the time. Amazing what GM does from time to time.
>
> BobR.
>
> Walter Sherwin wrote:
>
> > Or, when the high rev WOT SYNCH TBI pulses are too long versus the
available
> > REF pulse logic headroom...........
> >
> > Walt.
> >
> > >
> > > Generally yes. On a tbi ecm gm set it up to use async pulses for an
> > > accel
> > > enrichment. They sputter asynchronously between the normal sync
pulses.
> > >
> > > The other time async is used, is when the sync pulses get so short
that
> > > they can not meter fuel accurately enough. The ecm will switch to
async
> > > pulses until the required sync pulses are large enough again.
> > >
> > > BobR.
> > >
> > >
> > > Jeroen Proveniers wrote:
> > >
> > > > Hello,
> > > >
> > > > is asynchronous firing of the injectors necessary, except when
starting?
> > > >
> > > > I'm currently investigating the use of a PLD (Altera MAX7000S) to
> > implement
> > > > all the timing logic for injection and ignition, so when async
firing is
> > an
> > > > absolute requirement I've to account for it.
> > > >
> > > > Short description of the PLD:
> > > > The PLD is aimed at sequential injection. Synchronisation to the
engine
> > is
> > > > by 2 sensors at the camshaft. Injection start can be controlled by
the
> > main
> > > > controller. In fact, sensor one gives 60 pulses per revolution that
> > > > decrements a counter, while the other sensor resets the counter to a
> > > > predefined value (reset value). When the counter is at zero it's
> > reloaded
> > > > with the reload value at the next pulse. At terminal count an other
> > counter
> > > > is kicked that selects the injector, and injection is then started
by
> > > > kicking a oneshot timer (16 bits, clocked at 1MHz).
> > > >
> > > > So injection starttime can be controlled by changing the reset
value.
> > The
> > > > reload value is fixed as it defines the number of cylinders.
> > > > I'm also thinking about stopping injection when intake valves close,
> > instead
> > > > of starting injection when the valve opens.
> > > >
> > > > JJ
> > > >
> > >
> >
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