Broken turbo, now Injector pulse width at idle...

[ECMnut at aol.com]

Dave wrote:
>  Just remember that the whole 2.4ms isn't fuel spray... the injectors have
>  some latency on open and close so you're probably closer to 1.8-2.0ms
>  actual open time

2 ms sounds about right to me for an idle pulse width and
Dave said a mouthful.  There are lots of variables that the ECM
takes into account in this regard..  There is actually a table
in the Turbo 749 chip to allow compensation for the time required 
to open the injector.  I believe it is a *time vs. battery voltage*
 table.  Another interesting point is, when you are firing the
injector twice per intake valve event, or once every RPM,
your *minimum possible fuel volume* is sometimes too great
to support a "clean" idle  This is especially true in turbo engines
where you may need a big injector to keep it fed at high rpm/boost
levels.  To combat this problem, the ECM has the ability to switch
to "quasi-asynchronous" fuel delivery (QAFD) mode...

This happens when the fuel injector pulse width becomes 
too small to assure accurate fuel delivery..  I think that the QAFD
threshhold is somewhere close to 2ms for a typical suturated
MPFI injector on a GM ECM, but that is just a guess...

Quasi-asynchronous mode will fire the injector only once
per intake event, B-U-T for twice the duration..This results in 
a more accurately metered fuel flow under low demand
conditions..  I hope that came out right...8~)

What I cannot figure out is, how to determine if the ECM
has gones into quasi-asynchronous mode, when all I have
for wathcing the activity is a diacom or OTC..
Mike V