Injector control question

[Seth]

On Fri, 22 Aug 1997, Tom Cloud wrote:

> I wrote:
>  
> >> In examining my Holley ProJection (model 502 analog) I find
> >> that the pulse width to the injectors is a constant (approximate)
> 
>         [ snip ]
> 
> >> NEXT ...
> >> 
> >>    Some time back (few weeks ago) there was a question
> >> about building a meter to monitor the PW of injectors
> 
> and Bruce replied:
> 
> >About a year ago, I made such a meter out of a PIC 16C56 chip
> 
> but Bruce, you didn't address my primary query -- that
> being:
> 
>         "why does one want to know the PW when it's the
>          duty cycle that's impotent (regardless of whether
>          one uses fixed PRR/var. PW or fixed PW/var. PRR) ??
> 
> Am I incorrect about that ??  I recognize that there's going
> to be errors in fuel delivery calcs at the opening and closing
> of the injector, so short pulses would deliver less fuel/time
> than long pulses and this would imply that a simple duty
> cycle measurement would have some inherent errors, but I'd
> think they'd be minimal.
> 
> IOW, seems that duty cycle is what you want to measure, not PW ????
> 
> 
> Tom Cloud
> 
>         Ever stop to think .... and forget to start again ??
> 
Why would you want to know the duty cycle?  Other than determining if you 
break 85% and rick holding the injector open...  If you have a sequential 
port efi, wouldn't you align the injectors in phase with the intake 
event,, so frequency would vary with rpm, then adjust pulse width 
according to volumetric efficiency at that point (determined by MAP or 
throtle position).  That is what I am designing around with my 68HC11 
project.  They duty cycle is all over the map from ~1.5% to ~85%, but the 
pulse width is from 1.5ms to 18 ms.  Maybe I am overlooking something?


Seth