MicroSquirt.com read only forum (Jan.15,2018)

does anyone know the purpose of having PWM threshhold based on the MS manual? Is there a significant effect on the amount of delivered fuel when changing the PW duty cycle?

Both the threshold and PWM duty cycle are parameters that are used to "tune" a particular injector for proper operation. They are not used to change the fuel delivery in any way, they are set once when you install the injectors so that 1) it opens properly and 2) doesn't melt due to current overload.

Eric

isnt the PW supposed to be the required time to be able to deliver the right fuel? it seems to me base on the picture that putting in the threshold would actually reduce the time of fuel delivery as well as opening time.

and also does anyone know if the generation of PW occurs only during spark events?

by the way, thanks for the reply!

No, PWM is the means by which current is limited so that you don't burn up lo-z injectors. Injection PW is something competely different, it is the time that the injector is turned on to deliver fuel, don't confuse the two.

Yes, injection events only occur at ignition events in all current code variants.

Eric

thanks for the rep again!

if the PW threshold is a part of the total PW, shouldnt it be included it the PW equation?

maztah wrote:if the PW threshold is a part of the total PW, shouldnt it be included it the PW equation?

No, the PWM threshold has nothing to do with the fuel PW equation, it is a hardware setting that tells the injector driver when to limit current so as not to burn up the injector.

Eric

maztah

The injectors require a large current to initially open and a smaller current to keep them open. So initially 12V is applied to open them quickly. Once open (~1ms) PWM is applied which is essentially a smaller voltage/current to keep them open.

oh now i get... thanks a lot!!