Asynchronous injection (and PLD)

rr RRauscher at nni.com
Sat Jan 27 13:40:48 GMT 2001


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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