7749 ECU PW musings.....

[nacelp]

> 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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