Looking at the % of time injectors are open
 

:confused: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.

Injector duty cycles can be read from the ECU but so far as I know no other way.

Cheers , Pete.

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.

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.

:)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.

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).

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.

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.

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?

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 :p).

My goal has sort of evolved during this conversation.

This is my ultimate objective.

"seeking an inexpensive way to look at real time relative fuel flow for those people who can't afford a computer."

the way this 91F250 works, 'key prwr on' puts 12vdc on the 8 injectors full time, then the ECU grounds 4 injectors at once each revolution.(crude but half way effective)


So what is the best way to display the duration of that injector pulse?
For the least cost?

UNder economy conditions, my Analog meter is operating down in the 0 to 15% part of the scale. The reason I started down this path is because everyone either has a dwell meter or knows someone that has a dwell meter in the bottom of their box gathering dust.

This basic problem is probably why "digital" was invented. My electrical knowlege is obviously limited. If the best compromise between cost and ultility is a digital readout then what instrutment would give the most bang for the bucK? For people on a limited budget that is probably around 20 bucks.

I appreciate everyone patiently listening to my ramblings. For some reason my thoughts do not develop unless I put them out here on paper. But based on the number of pre-ODBII vehicles on the road, and what we modders know about real time feedback to the driver, I think there is a huge benefit to be realized if we can find an inexpensive way to display relative fuel flow beyond what a vacuum gage will show.

Does the dwell meter you are using have switchs for 4, 6 and 8 cylinders, or does it just have 3 different scales. If it has the switch, try going to 4 cylinder mode.

Your right, I do have a old dwell meter, I just hadn't considered using it in this manner. It isn't a perfect solution, but it is more information and to a large extent it is all really relevant to what speed I am driving and how I'm doing relative to it. I'll have to give it a try.

the dwell just has one position and 3 scales, but i can make my own scale to read in GPH. the tach has three positions of course. the dwell of the injector pulse is directly related to fuel flow per unit time. Dwell is not directly related to RPM, that fooled me for a while. when i am stationary this KEL mileage computer reads in GPH. and i can set no load idle at 1k, 2k ,3k, 4k, RPM for example and the injector dwell tracks with the GPH not with the RPM. If i had an extra injector hooked to the fuel line and squirting in a graduated cylinder and wired up to one injector. And i ran my engine for 6 minutes at a constant dwell. Then i could calculate my fuel usage per hour at that dwell. And then when i'm out driving at that dwell number i would still be using that amount of fuel per hour. Amount of fuel sprayed in 6 minutes at steady speed X 10 X the number of injectors=fuel per hour. If i'm driving at 60 miles per hour then i'm going one mile a minute. From the previous sentence GPH / 60 = GPM. At 60 miles per hour, that gives me gallons per mile. Invert that and i have miles per gallon. i can figure it out once make up table to hang on the dash. does not matter what gear or RPM's. my dig is my meter has a small face and i can't see small changes. i am going to look at bigger meters and the digital duty cycle meters some more, but the least expensive digital i saw with a quick google was $60. my DVM doesn't have duty cycle. actually my dwell meter just happens to be 1 milliamp. full scale so i could tap into that and read thousands of an amp. on my DVM. i got to take the wire off one side of the milliamp meter and connect the DVM in series with it.

diesel_john -

Would this fit the bill? :

LED Duty Cycle Meter for Fuel Injected Cars - US$42.31
http://autospeed.com/shop/category_579/browse.html
http://us1.webpublications.com.au/st...03707465hi.jpg
I don't think you would need it to operate an extra injector, but it appears to at least show the magic pulse number you are looking for.

CarloSW2

That would work, now $42 is the price to beat. my extra injector procedure would calibrate it if they don't total the squirt time. if they keep track of the total, then it is a flow meter, and all i got to do is go out and run a gallon though it and the number i get is the fudge factor. the preset level could be a shift light.

i am amazed they don't sell a flow meter made like this. The market is huge. all the cars and light trucks made from 1985 to 1993. Many are gas guzzlers and every single person who has one is wondering (even if they won't admit it) how in the heck can i reduce my gas bill? And who will buy it when ican no longer afford it?

a duty meter is almost instanteous. a flow meter would have a slight delay, but nothing like a mileage computer.

would it be possible to put this thread in the instrumentation category or somewhere more pertinent.

Done :thumbup:

diesel: "now $42 is the price to beat"

I realize that this thread is stale, so maybe you're not watching, or you've found a different solution. But just in case, I thought I would mention this. Harbor Freight has a DMM with a dwell feature:

http://www.harborfreight.com/cpi/cta...emnumber=95670

$32.99, plus shipping (about $8, unless you walk into their store).

I just got it, and it works fine (set to dwell) for monitoring my injectors (VX). Also works fine to monitor my O2 sensor (although I can't monitor my O2 and my injectors at the same time, obviously).

That's cool, I am also following the development of the MPGuino.

Here is a simple circuit that should let you use any old voltmeter (analog or digital) as a fuel injector monitoring device. You can adjust the two potentiometers to suit you, i.e. to put the needle in the range you want it to be in.

The transistor is a NPN small signal switching transistor such as the very common 2N3904.

The diode is any silicon diode such as a 1N4001 etc.

The 10k resistor on the input wire insures that this will not affect your injectors or ECU's circuitry since they operate at a very low impedance and this is around 1000 times higher.

None of the component values are too critical since you use the two pots to adjust it to suit.

The "to inj." wire goes to the same place you are hooking the dwell meter.