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

Tue May 24 11:00:48 UTC 2005

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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