[Diy_efi] Measuring Pulse Width/Duty Cycle of an Injector?

Tue May 24 12:01:01 UTC 2005

some EFI's have a curve for correction of inj duration related to voltage. my EFI adds 0.85 msec at 12V

> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org 
> [mailto:diy_efi-bounces at diy-efi.org]On
> Behalf Of Marcello A. Belloli
> Sent: Dienstag, 24. Mai 2005 13:01
> To: diy_efi at diy-efi.org
> Subject: RE: [Diy_efi] Measuring Pulse Width/Duty Cycle of an 
> Injector?
> 
> 
> Steve,
>     I follow exactly what you are saying.  What I am figuring 
> is that the
> valve will do the same thing every time, or close to it.  So the
> inaccuracy should be a constant thing.  What I want to look at are the
> differences, not so much the exact reading.  So if I bump up the fuel
> table a notch, can I see the difference.  I figure I should be able to
> cancel out the constant of error.  And just look at the delta of
> injector time.  I could easily be wrong.  But I'm going to give it a
> try.
> 
> Marcello
> 
> 
> 
> > I've never characterized it's accuracy.  In fact, I haven't 
> really used
> > it other than testing it a few times to see if it worked.  Too busy
> > doing things like replacing worn out steering boxes to have 
> time for the
> > fun stuff.
> >
> > Anyway.  Getting 2 significant digits from a pulse width 
> meter would be
> > tough enough, 3 or 4 as you've indicated below is right out.  The
> > injector probably spends half a millisecond somewhere 
> between open and
> > closed every time it's fired and it's flow rate is 
> undefined during this
> > period of time.  With that kind of uncertainty in fueling getting a
> > bunch of decimal places on the pulse width measurement 
> probably isn't
> > that useful.
> >
> > It should work fine on P/H circuits, as long as the voltage to the
> > injector doesn't go below the forward voltage drop of the 
> diode, which
> > is probably something like 1.2 volts?
> >
> > Remember that your scanner is telling you what the computer 
> wants the
> > injector to do, which isn't necessarily what the injector 
> is doing, if
> > there's a defect somewhere in the circuit or one of the injectors.
> >
> > --steve
> >
> >
> >> -----Original Message-----
> >> From: diy_efi-bounces at diy-efi.org
> >> [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Marcello 
> A. Belloli
> >> Sent: Monday, May 23, 2005 10:56 PM
> >> To: diy_efi at diy-efi.org
> >> Subject: RE: [Diy_efi] Measuring Pulse Width/Duty Cycle of an
> >> Injector?
> >>
> >> Steve,
> >>      With your setup how accurate can you get?  All the
> >> scanners I've used
> >> in the past to look at cars gave readings in the x.xx ms range.  At
> >> idle I've seen cars that started running rich, or lean based on the
> >> o2 reading and seen no change in injector pulse width on 
> the scanner.
> >>  I see the computers short term / long term trim values change, and
> >> yet the IPW reading never changed?  I am guessing I need another
> >> order of accuracy like x.xxx ms to see these changes at 
> idle.  Do you
> >> think I could get that out of your circuit.  And how does 
> it handle a
> >> Peak Hold type injector?  This is the most important piece of data
> >> I'm grabbing to try and do what I want to do in the end.  I'm going
> >> to go grab the details to your project right now, and check it out.
> >>
> >> Thanks,
> >>
> >> Marcello
> >> >
> >> >> -----Original Message-----
> >> >> From: diy_efi-bounces at diy-efi.org
> >> >> [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Marcello
> >> A. Belloli
> >> >> Sent: Saturday, May 21, 2005 10:31 PM
> >> >> To: diy_efi at diy-efi.org
> >> >> Subject: [Diy_efi] Measuring Pulse Width/Duty Cycle of 
> an Injector?
> >> >>
> >> >> Hello Everyone,
> >> >>      I'm still working on a datalogger project.  Been doing a
> >> >> lot of the
> >> >> software while I've been on vacation in Thailand. I'm still on
> >> >> vacation, but can't keep my mind off of this project.  
> I'm using a
> >> >> PIC18F452 as the Micro behind my datalogger.  I've got 
> just about
> >> >> everything working.  The one place I'm having problem is the
> >> >> understanding of how to read pulse width of a fuel injector.
> >> >>      Is there a way of looking at all types of injectors,
> >> >> that will allow
> >> >> for an accurate account of timing?  I've been looking at
> >> two type of
> >> >
> >> > For the pulse width meter I built (see the diy-efi.org
> >> projects page) I
> >> > used an opto-isolator to both insulate the measuring
> >> circuit from the
> >> > injector circuit, and make it able to hook up across the 
> injector no
> >> > matter which side of the injector is driven, or what the voltage
> >> > waveform looks like.  This particular opto-isolator has 
> 2 diodes in
> >> > parallel, so the polarity of how it's connected doesn't
> >> matter -- if the
> >> > injector fires, then one of the diodes will light up and
> >> complete the
> >> > circuit.
> >> >
> >> >> injector firing.  Low resistance injectors, which use a 
> driver that
> >> >> duty cycles the injectors after the main firing to keep 
> the current
> >> >> within limits.  And Higher resistance ones where the
> >> resistance alone
> >> >> keeps the current down.  Now how do you look at firing 
> time of an
> >> >> injector when the driver starts to duty cycle it after 1.2ms?
> >> >
> >> > I haven't see all driver circuits out there but I think 
> most of them
> >> > don't duty cycle the injector, they just reduce the voltage
> >> applied to
> >> > the injector.
> >> >
> >> > --steve
> >> >
> >> >
> >> > _______________________________________________
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> >> >
> >>
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