7749 ECU PW musings.....

[Dave Zug]

This may be nothing.. but is there a published pintle speed, or amount of
time from OPEN to CLOSE and vise versa, flow characteristic (curve) for
varying pintle positions (10,20,30,.. %) for a given injector?  What I'm
getting at.. If the amount of time that the injector is to be CLOSED is less
than the amount of time it actually takes the pintle TO close, then you wont
get a CLICK noise as it closes.. it will start opening again.  "pintle
float" ??


----- Original Message -----
From: nacelp <nacelp at bright.net>
To: <gmecm at diy-efi.org>
Sent: Sunday, May 14, 2000 8:25 AM
Subject: Re: 7749 ECU PW musings.....


>
> > Been doing some more scoping, and have some observations and questions -
> > While running the benchtop ECU and reading injectors on the scope, I
> > noticed that the injector 'buzzing' sound stops *before* the electrical
> > pulses to them go flat-line (100% duty cycle).  This happens @ around
80%
> > duty cycle; now, granted, this is running in air, w/o any fluid or
> pressure
> > in the injectors.  But, I would assume that the viscosity of fuel in the
> > injectors, as well as the pressure of the fuel, would tend to *enhance*
> > this, not degrade it.  So, 100% *electrical* and *mechanical* duty
cycles
> > appear to be different things.
>
> > Furthermore, per ALDL data stream info, they "max out" (go static = stop
> > buzzing) at an indicated 'on time' of 10ms @ 3000 RPMs, where there's
> > 20msec available 'on' time. This I do not understand.  The *major*
factor
> > in determining PW is manifold pressure, as you'd assume; cranking this
pot
> > really changes PW.  The other factors (temp, TPS, etc) provide a 'trim'
> > depending on engine operating parameters.
>
> Don't mistake a cut out, as going static.
> Are the injectors actually On, or Off?.
>
>
> > In the data stream, there's also two bytes that supposedly give "Time
> > between reference pulses" (bytes 11 & 12 = OLDRFPER, OLDRFPER+1, MSB,
> LSB).
> >  This value *increases* linearly w/ RPMs, not inversely as you'd (I, at
> > least) expect.  If injector events happen on reference pulses, its
> > bassackwards.
> > Can anybody help out here?  I'm going to be trying to burn a good 40#
chip
> > for my modded Sy, and I'd like a little more correlation between
> > "empirical" stuff, what actually works, and theory.
> > My scope indication of "on" time of the injectors and what's reported by
> > the data stream are radically different, also.  Wrong both absolutely &
> > linearity wise.  I don't know what's up here.
>
> I was begining to wonder what I was doing wrong.
> Grumpy
>
> > Thanks for any feedback - Barry
>
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