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Old 03-03-2008, 01:11 AM   #1 (permalink)
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Looking at the % of time injectors are open

What would the circuit look like that could sum the short pulses of two fuel injectors together? So that an inexpensive duty cycle meter or dwell meter would be operating up closer to mid range.


Last edited by diesel_john; 03-04-2008 at 12:43 AM..
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Old 03-03-2008, 03:12 AM   #2 (permalink)
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Injector duty cycles can be read from the ECU but so far as I know no other way.

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Old 03-03-2008, 07:27 AM   #3 (permalink)
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Pete,
on a gasoline MFI engine, i just use an analog breaker points dwell meter to look at the degrees that an injector is open by connecting at the injector.

during hypermiling the needle stays in the bottom 20% of the meter.(seepost7) i was trying to figure away to get the meter up in the center of the scale.
it would be a real time based relative fuel meter.

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Old 03-03-2008, 08:27 AM   #4 (permalink)
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If you had a multimeter that measured duty cycle you could just measure duty cycle off one injector since all of them are at the same duty cycle.
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Old 03-03-2008, 08:47 AM   #5 (permalink)
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i usually try to reinvent the wheel, I was thinking analog meter, but will check price on the multimeter. seeking an inexpensive way to look at real time relative fuel flow for those people who can't afford a computer.

i found duty cycle meters as low as the $60 range.

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Old 03-03-2008, 11:30 AM   #6 (permalink)
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Have a laptop?

A diode clamp, resistor and headphone jack can be used as for measuring duty cycle... But, it's not real time (you have to go back, zoom in and look at the waveforms).
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Old 03-03-2008, 02:11 PM   #7 (permalink)
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i tried my old home made dwell meter again and it worked this time, i don't know what i did wrong last time i tried it.
Any how, i turned up the pot that adjusts the needle to 100% 'duty cycle' to maybe 125% and i got pretty good correlation with my flow meter.
10% was ~1 gph and 20% was ~ 2 gph 30% was ~2.9gph and so on.
And the response is immediate, almost too fast, because at idle the needle bounces.
As before, i was thinking, if there was way to add two injectors together, the needle would be in the center of the scale and more stable. my meter is 1 MA full scale.

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Old 03-05-2008, 01:41 AM   #8 (permalink)
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Quote:
Originally Posted by trebuchet03 View Post
Have a laptop?

A diode clamp, resistor and headphone jack can be used as for measuring duty cycle... But, it's not real time (you have to go back, zoom in and look at the waveforms).
do you know if the time base can be changed on a duty cycle meter. to effectively 'zoom' in time. it would be nice if i could just slow down time by 50% so full scale on my meter was a half duty cycle. the injector is not open 50% until i am high load and high RPM. so i never need the top half of the scale for economy driving.

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Old 03-05-2008, 02:10 AM   #9 (permalink)
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Seems like you've found a solution. I was going to suggest treating it like a binary problem. I'm assuming your injectors are fed a constant voltage to be "on" over a period of time then off again, so sampling that +voltage line and then dividing it over a time window should let you figure it out?
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Old 03-05-2008, 10:33 AM   #10 (permalink)
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Quote:
Originally Posted by diesel_john View Post
do you know if the time base can be changed on a duty cycle meter. to affectively 'zoom' in time.
No clue... I imagine some can and some can't... You'd probably pay for more for the ones that can (if such a beast exists ).

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