Injector control question

[Tom Cloud]

>> >> 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

>> 
>>         "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 ????


>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?

 - one, I'm using TBI (or CPI) not TPI, so the relation of
the injector firing to my actual valve opening is not
important (is it ??? ).

 - second, the duty cycle is the amount of fuel you're delivering --
depending on the pressure differential across the injector, the
injector "rise" and "fall" (open and close) times, etc.

I'm asking because I don't know ..... still seems to me that
knowing the duty cycle is more important (and much easier to
measure) than actual pulse width time.  If you're worried about
 *when* the pulse is triggered relative to the valve opening
(I assume we're talking a certain no. of degrees from TDC),
then that's another kettle a'fish again -- isn't it?

If you know the duty cycle and the rpm you can deduce the
pulse width -- but not with great accuracy (depends on the
accuracy of your duty cycle and rpm measurement).

Tom Cloud

        Ever stop to think .... and forget to start again ??