[Diy_efi] How many Bits for PWM injection driver?

[Stephen Webb]

> I tried several archive searches, but didn't see any mentioning if
> 8 bits would be too coarse. My gut feeling is that I could live with
> 256 steps.
> Would it be noticeable during mild throttle settings?

Not speaking with much authority on the subject, my gut reaction is that
256 steps is enough, but ideally they wouldn't be equally spaced.  

If they are equally spaced, you may have a "dynamic range" problem, or
your steps will be too big in the low end.  If you use 50 times as much
fuel at peak torque as you do at idle, your idle PWM setting (on your 256
step scale) would have to be about 5.  Go one step either direction and
you've changed the amount of fuel you deliver by ~20%.   Bump up your
"idle PWM" value to 20 or so, and you only get a 5% fuel change per step
(in the low end), but you can only deliver 10x as much fuel at full load. 

-Steve



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