Pulsed injectors on/off times

[isham-research.freeserve.co.uk at pop.pol.net.uk]

> There is a problem, the 80-85% rule must be obeyed. But I also suspect that
> some injector drivers are more sensitive then other. The back emf issue was
> something a friend and I discussed a few weeks ago, we tried to understand
> why the injectors floats above a certain duty cycle.

Does anyone have an equivalent circuit for the injector?

Almost all switched automotive components produced over the last three
decades have had internal suppression across windings - sometimes a
simple capacitor, sometimes a diode.  As duty cycle increases, a larger
percentage of total time will be governed by the actions of any such
circuit.

> Of course the problem is rpm related, 98% duty cycle at 10Hz isn't a
> problem. The EMF as I see it is caused by the injector plunger falling
> through the winding. I can't see how that opposing force can help opening
> the injector. Either way, if it isn't EMF that causes the problem something
> else is. The problem with injector float is very real.

A coil protection diode would be biased against the applied operating
voltage.  Any flow through it when that voltage is removed would be in
the same direction through the coil, acting to open the injector.  The
problem I have is a lack of quantitative appreciation - is this current
significant, or it is too small?

As I think Orin said, you'd be better off to take this discussion to
diy_efi - there are guys there who know this stuff.

-- 
 Phil Payne
 http://www.isham-research.freeserve.co.uk/quattro
 Phone +44 7785 302803   Fax: +44 7785 309674