Pulsed injectors on/off times

[Jorgen Karlsson]

Hi,

> No, you've just created a whole lot more!

Ok, I will try to set things right...

> I'll start with this part because I can't follow it in the context you've
> described below (sorry I'm no engineer)
>
> "100% is OK! 85-99% is begging for trouble"
>
> Earlier in the paragraph you mention that some don't fire at 100% so how
> does this fit?

I didn't directly say that they don't fire at 100% I say that they cannot be
trusted to open and close correctly at more then 80% Pulse width. This is
also rpm dependant. But on most car engines 80% is a good rule. But for
example on a Honda CBR 250cc 4cyl 4stroke motorcycle with a redline at more
then 20000rpm, something like 50% is more like it at high rpms. But lets
assume that the engine we speak about don't rev more then 6000-9000rpms.

The thing that happens is that when the injector don't have time to close
before it is commanded to open it will cause back EMF (electro magnetic
force). The impendance of the injector gets soo high that the current over
the winding builds slowly. This in turn makes the injector take a very long
time to open, then when it has opened it all happens again as it is
commanded to close. This is how the injector can stay half open even if it
is commanded to be open 95% of the time.

If the injector is in the abouve state where it floats in the middle of the
stroke and the voltage over the injector is then kept on for for a longer
period. For example 50mS, the injector will have time to settle i the open
possition. This is how 100% is ok but 95 isn't.

The part where an injector won't open at all is an other matter, this is
related to fuel pressure. This is because the injectors open inwards and the
fuel pressure help keeping the injector closed. On most injectors this is
not a real problem since they can handle fuel pressures up to 80psi or soo.
I mentioned the Rochester injectors since some of them can have problems at
50psi...


Jorgen Karlsson
Gothenburg, Sweden.