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Old 03-14-2009, 07:28 PM   #1 (permalink)
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Love it but very very confused

This has to be one of the coolest things ive seen in a long time.. now maybe I dont get out much but I like knowing the details of how my vehicles work and this is just for that.
That being said, the Devils in the details. You should be able to find the numbers for injectors etc and plug them in and be pretty darn close. But Im not even close to "close" with my numbers.
I really wish someone could tell me why my actual usec/gal is soo far off from the computed value.
For my two 55# TBI injectors I get a computed usec/gal of 196,363,636.36 The 68# injectors give a smaller number that is still Way too big.

The actual number is closer to 0038,823,529. I should be able to get closer then this without having to wait for a tank of fuel to be run through.

What exactly is a usec/gal anyway? I have read sooooo many threads but still haven't seen usec explain in a logical way that makes sense. It is technically micro seconds per gallon right?
Is this basically just volume of that particular injector? Hmm but then what exactly is a micro second?

Ok someone correct me if Im wrong. I never was really good at the math stuff. I found this definition on the net.
A microsecond is '''one millionth (10^-6) of a second; one thousandth of a millisecond'''

Ok then if I am figureing this right then to convert to seconds one would have to take that huge long number and divide by how many zeroes are in a million.
Hmm 196,363,636 \ 1000000 = 196.36 seconds. So it should take this injector at 13# of pressure 196.37 seconds or 3.3 minutes to fill one gallon gas can of fuel?

Lets try that with the actual(best estimate based on known mpg)
38,823,529 \ 1000000 = 38.82 seconds. So using the above computation I could fill a 1 gallon gas can in 38 seconds.?.? Uhhh is this even possible? I am very confused. I have a headache, Can someone make sense of this?

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Old 03-15-2009, 10:10 AM   #2 (permalink)
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1 microsecond, or µsec, = 1.0 × 10-6 seconds. Simply 1 µsec = 0.000001 seconds.
This is territory I haven't entered yet, but the MPGuino guys will answer this better than I can. I believe that Injector pulses are 2 pulses per rotation, open and close, and this is part of the rpm, so 6000 pulses would be 3000 Rpm, then a certain number of pulses = 1 gallon of fuel dispensed.
I hope I am right, but please disregard If I am later proven incorrect. I know I am right on the conversion though .
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Old 03-15-2009, 12:11 PM   #3 (permalink)
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I've never tried to compute usPerGallon. Since you can derive it by comparing fuel used at a refill, it seemed an academic exercise fraught with variables.

it represents the amount of time the in microseconds the injectors would have to stay open in order to dispense a gallon under actual operating conditions. injDelay (again in microseconds) is subtracted from each injector pulse.
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Old 03-15-2009, 01:25 PM   #4 (permalink)
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Quote:
Originally Posted by dcb View Post
I've never tried to compute usPerGallon. Since you can derive it by comparing fuel used at a refill, it seemed an academic exercise fraught with variables.

it represents the amount of time the in microseconds the injectors would have to stay open in order to dispense a gallon under actual operating conditions. injDelay (again in microseconds) is subtracted from each injector pulse.
Thanks dcb, Did you find anything wrong with my computational comparison between injector actual and computed? I feel I must be doing something wrong in computing the injector flow rate to be off that far.
Either that or I am getting confused by number of injectors versus cylinders. I know most of you guys are running smaller cars where you have 1 injector per cylinder, which is most often 4 to 4. But I am running 2 injectors for 8 cylinders. Seems to me that should figure into the math somehow but I haven't quite figured out how.
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Old 03-15-2009, 01:56 PM   #5 (permalink)
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I don't know, I just measure it with the gas pump

There's lots of variables as I said. I would just top off the tank and fudge usPerGallon so that mpg looks about right, then true it up at the next fillup.

But in essence, it is the pressure drop across the injector that determines the flow. If you know the operating pressure drop and adjust the published flow rate for the operating pressure drop in your vehicle, you can multiply that by the number of injectors to try and predict how much flow per time total.

Also, you did not mention what vehicle you have. There is a known issue with peak and hold. Just as a precaution you might want to unplug an injector and measure it's ohmage, if it is above 10 ohms you should not have a problem.
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Old 03-15-2009, 04:18 PM   #6 (permalink)
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Quote:
Originally Posted by dcb View Post
I don't know, I just measure it with the gas pump

There's lots of variables as I said. I would just top off the tank and fudge usPerGallon so that mpg looks about right, then true it up at the next fillup...
Exactly! Don't get wrapped up in the name, i.e. uS/gal. Think of this as some arbitrary unit of time that your injector must stay open on average to spray one gallon of gasoline.

But your injector is an on/off device. It doesn't stay open all the time. Rather, it is pulsed on for a few units and then off again for a bunch of units. Your engine control computer determines how many times per second and how many units it stays open. Sensors for RPM, temperature, load, and many other values are fed to the ECU. The ECU then adjusts the number of times per second the injector is opened and for how long. Keep in mind that a TBI injector isn't necessarily opening and closing in synch with the engine RPM. It's just that the average amount of time it's open has to be the number of units needed to spray gasoline at the proper fuel/air ratio.

I also tried to calculate my injector fuel flow but was waaay off. After wrestling with the calculations for a week, here's what I did instead.

I zeroed in on my uS/gal number by driving at a steady speed on a level highway and, based on my previous fuel log, guessed that I'd be getting 21 MPG. I pulled over several times, adjusted the uS/gal setting up or down, drove again at the same steady speed until I saw 21 MPG on my MPGuino. That got me in the ballpark. As it turned out later, I was within 1% of my best calibrated uS/gal.

Then I started the fillup-fillup-adjust cycle. (1) Fill the tank, reset the car odometer, reset the MPGuino tank values. (2) At the next fillup, note the gallons needed to fill the tank, note the gallons the MPGuino says you used, do not reset the tank values yet. (3) Adjust the uS/gal setting up or down and then check the MPGuino tank gallons used again. It will recalculate up or down depending on your setting change. Keep adjusting the uS/gal number until the tank gallons used is the same as the amount of gas you just put in the tank. Now you're calibrated very close. Do the same over the next couple of tankfulls to get the calibration even closer.

As dcb says, you need to identify the type of injector. In its basic form, the MPGuino is not designed to handle peak and hold injectors. If yours is that type, you've got some work ahead of you in both hardware and software.
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Old 03-16-2009, 12:41 PM   #7 (permalink)
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Quote:
Originally Posted by Funny View Post
1 microsecond, or µsec, = 1.0 × 10-6 seconds. Simply 1 µsec = 0.000001 seconds.
This is territory I haven't entered yet, but the MPGuino guys will answer this better than I can. I believe that Injector pulses are 2 pulses per rotation, open and close, and this is part of the rpm, so 6000 pulses would be 3000 Rpm, then a certain number of pulses = 1 gallon of fuel dispensed.
I hope I am right, but please disregard If I am later proven incorrect. I know I am right on the conversion though .
Almost correct. A single injector (port injector type, not TBI)) will be pulsed open for some number of microseconds once in two revolutions of the engine. The MPGuino is tracking the moment in time when the leading of the pulse occurs and then when the trailing edge occurs. Time, in this case, is measured in microseconds, i.e. millionths of a second. The time of the leading edge is subtracted from the time of the trailing edge to get the elapsed time of the pulse. All of the elapsed times are added together to get the total amount of time that the injector is open. After you've calibrated the number of microseconds it takes to spray one gallon, that number is divided into the total time to get the number of gallons sprayed.

For example, if the total open time is 1,455,788,104uS and you have calibrated the fuel usage as 200,500,000uS/gal:

1,455,788,104 / 200,500,000 = 7.26 gallons

So, there's nothing magic about the total microseconds. It's just the total elapsed time that was needed to spray 7.26 gallons. Once you've calibrated your fuel usage, it should consistently indicate the gallons used.
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Old 04-09-2009, 03:45 AM   #8 (permalink)
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Quote:
Originally Posted by dcb View Post
I don't know, I just measure it with the gas pump

There's lots of variables as I said. I would just top off the tank and fudge usPerGallon so that mpg looks about right, then true it up at the next fillup.

But in essence, it is the pressure drop across the injector that determines the flow. If you know the operating pressure drop and adjust the published flow rate for the operating pressure drop in your vehicle, you can multiply that by the number of injectors to try and predict how much flow per time total.

Also, you did not mention what vehicle you have. There is a known issue with peak and hold. Just as a precaution you might want to unplug an injector and measure it's ohmage, if it is above 10 ohms you should not have a problem.
So sorry for being absent for so long. I have been having a rough time trying to get a tank reading. the mpguino unit locked up twice on me out of the clear blue. no hint either time. I refilled and reset it and got almost half way through another tank when I acidently hit the two reset buttons together.. ugh. But I am sitting at 312 miles and still havent hit the half way mark so I dunno if I broke my guage or im doing something right. Im leaning towards the guage being bad lol. because I cant get that silly guage to make much sense. Sometimes it says im getting 14 mpg on fairly hard acceleration but only 9 on a gentle throttle. Then there is a really touchy spot where it will jump up to 23 mpg. If the road is level you can keep it there usually. One hair more throttle and it will drop straight to 12 or 13 mpg. Coasting very rarely gives more then 24 mpg unless I stick it in neutral at about 55 and i can get roughly 34 mpg once 40..
I got to get a wideband on this thing.
It is a 1993 suburban with the 350 engine. I am thinking of building a new engine for it, that would have the benefit of 10 to 1 compression and better breathing and valve timing.
But it just wont DIE, without which the wife wont approve the funds..
Course I could just let her drive it more hmmm I got a personal junkyard with cars shes driven.. hmmm
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Old 04-09-2009, 03:49 AM   #9 (permalink)
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Quote:
Originally Posted by rmccomiskie View Post
Exactly! Don't get wrapped up in the name, i.e. uS/gal. Think of this as some arbitrary unit of time that your injector must stay open on average to spray one gallon of gasoline.

As dcb says, you need to identify the type of injector. In its basic form, the MPGuino is not designed to handle peak and hold injectors. If yours is that type, you've got some work ahead of you in both hardware and software.
they have the little orange colored rings on the terminal. I hooked my digital ohm meter to it and set it for 200 ohms. The reading I got was 1.7
So Im a little rusty on these digital meters.. is that 1.7 ohms? or 1.7*200?
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Old 04-09-2009, 08:58 AM   #10 (permalink)
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I'm pretty sure you have TBI peak and hold, we finally got some real world data on that in January and are still working on the solution.

http://ecomodder.com/forum/showthrea...sory-6863.html

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