[Diy_efi] Fw: Static injectors, and misc stuff, possibly a good read

[Bruce]

While GN specific, this does reflect a fair time investment in sorting thru
things, and might be an aid in tuning for some.   Often big injectors are
given a bad rap for the way they run, and I think some of it's from not
really understanding some of what's going on.   Without a good scanner, and
or ecm bench it might be hard to see what's going on, or misunderstand it.
If your really interested in the static injector stuff the Turbobuick.com
bullentin board usually has a thread or two going about trying to get by on
too small of injector, and running over 100% DC.
Bruce



----- Original Message -----
From: "Bruce" <nacelp at bright.net>
> I generally don't cross post, but at times, some stuff even thou it loses
> some of it's meaning, kinda is worth exposing to daylight.
> Anyway, from the 009 thread at Turbobuick.com
>
> Originally posted by
> Maybe we need to define what 100% dc truly means. Is that the max amount
of
> time the injector can be open including opening and closing time? How long
> does it take to open and close the injector? If 100% includes open/close,
I
> could see where pushing it to say 105% might eliminate the open/close and
> get a tinsy bit more fuel. Just trying to brainstorm here...
>  [/B][/QUOTE]
>
> Duty Cycle is a comparison of the on time compared to the total available
on
> time.
>
> Just to make the numbers easy.
>
> At 6,000 rpm, you have 10 msec for a crankshaft revolution, since the GNs
> use SEFI you have two revolutions for firing the injector so you have a
> total possible time of 20msec for a pulse width at 6K RPM.
>
> At 3,000 rpm a crank revolution takes 20msec, and again you have 2
> revolutions to get the fuel squirted.  So at 3K rpm you have 40msec.
>
> OK, stay with me..
> Since no one is going to take a crack at answering what going over 100%
> does, I guess I will, while doing this.
>
> Now at 6K rpm, if you have a pulse width of 16 msec your at a 80% DC. and
> we'll also say, that's a 12.5 AFR.
>
> Now at 3K the enigne is still the same size, so you'll want that same
16msec
> squirt of fuel to have a 12.5 AFR, but your doing that with a 40% DC.
>
> So, we can see that Duty Cycles have different meanings at different RPM.
> To say I have a duty cycle means one thing, to say I have a duty cycle of
> 106% at 6K means something else.
>
> If you hook a DC meter to an injector you'll see that DS pretty much
follows
> what is going on.   Using my lil $30 meter I see as much as a 6% error
thou.
> And that's a share in case no one notices.
>   The why for it to occur, I haven't nailed down yet.
>   One other item is that a change of several percent of PE vs RPM or TPS
> doesn't look to match a given percent of AFR or PW.  Again a share.
>
> OK, so we see that at different RPMs, PW can do the same thing, AFR wise,
> but be entirely different DCs.
>
> Soooo,
>   Once we get to where the injector is REALLY STATIC, what does increasing
> the DC do?.
>    It changes at what RPM the injector does go static.
>
> Now, think about what I posted about the 160 number, and what is really
> going on.   The so called big injector problems are from just telling the
> ecm part of what's going on.
>
> GM uses many training aids, and easy explainations for some of the stuff
> going on.   The MAF Tables and Scalers, are just a frequency to PW
> conversion.   Once you understand that then you can get away from the
Static
> Injector tuning, and actually get the calibration right.
>
> So now you have two choices, try and get close by getting an injector to
> static, and fooling with FP.   But, there is no way to really tune the
point
> at which the injector goes static, and that is why some chips run well on
> some cars and not so well on others.
>   When you get to divorcing the various characteristics of the tune, then
> you can blend things as you want.
>
> BTW,     , I do thank you for asking the guestions you did.
>
> If someone has some other clues about why over 100% works, I'd like to
hear
> em, and the ecm bench is still warm from the last 100 experimental chips,
so
> no biggy to venture forth an idea, and I'll run it on the bench to verify
> it.



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