DIY Fuel rate meter/injector duty cycle meter/GPH - Page 2 - Fuelly Forums

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Old 06-12-2008, 09:21 AM   #11
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You definitely need to hook it up to the injector wire. I'm pretty sure a TBI only has one injector, right? The point is that it reports duty cycle to you -- it reports time on vs. time off in percentage form. You will get meaningful numbers even though it's reporting for all cylinders vs. one cylinder.
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Old 06-12-2008, 11:36 AM   #12
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Thanks for the feedback. To your point, it's just a number for comparison. I just need to get into it. I'll report back but it may take alittle time till I can. Too bad real life gets in the way of real stuff.
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Old 06-15-2008, 01:13 PM   #13
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Just wanted to let you all know I did find the injector wires with alittle probing. The Haynes manual made no direct mention of it. On 4 cylinder scale at high idle it read 4.5 and at warm idle 1.5. Looks to be in the ballpark. I'll install a permanent in car set-up when I return from travel this week.
I've got several experiments lined-up to try including vapor/steam injection and hho. I'll keep you informed.
I think this will be a great evaluation tool. THANKS!!
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Old 06-15-2008, 08:49 PM   #14
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Quote:
Originally Posted by rlkwnc01 View Post
On 4 cylinder scale at high idle it read 4.5 and at warm idle 1.5. Looks to be in the ballpark.
Yes, that sounds about right.

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I'll install a permanent in car set-up when I return from travel this week.
In my own situation, I found it was very helpful to use a temporary setup for a couple of weeks. I feel like that taught me a lot about how my engine was operating. Then I felt there was no need for a permanent installation. Although I may end up with some kind of permanent device later on, as some point.

I'm just suggesting you live with a temporary installation for a while before you make a big commitment to something more elaborate. The temporary installation will help you formulate what your real long-term needs are.
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Old 06-15-2008, 10:02 PM   #15
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Hollycow,

So you wanna polute your thread with what we discussed in the other thread, or make a new one?

To recap what we talked about:

- Collect all that on a PC via sound card
- The injector tap provides
* Duty cycle = gas consumed
* RPMs
- A VSS tap woul provide
* Car Speed MPH
- Computer provides
* time

With all of the above we can make a program that detects

* MPG
* MPH
* GPH
* Which Gear is in use
* Gliding/Neutral

I saw another thread on collecting data with a PC sound card, which might not be fumesucker's (If I find it again I'll update the credits). That one thread had audio samples and a java applet to parse the audio.

Since I've decided I need to upgrade my skills from C to Java, that would be a good mini project for me.
I have some ideas on how to present the data to help analyze hypermiling techniques efficiency.
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Old 06-16-2008, 11:53 AM   #16
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Quote:
Originally Posted by sonyhome View Post
So you wanna polute your thread with what we discussed in the other thread, or make a new one?
Might as well pollute here, I can breathe that crap. I brought in your message from the other thread, too.

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I'm really slow at projects like that.
- This WE I stayed home, and got around to fix my CRV speakers
- ...and cut foam grill blockers for the CRV. Dunno if the foam worked, but got 30MPG @65MPH one way, and 26MPG @74MPH the other way (Short distances, flatish), without overheating apparently. Still warry to use that on long trips.
I'm slow too. I didn't do anywhere near as much as you did this weekend.

I'm going to rig up a light that tells me when my cooling fan is on so I can see if it runs more after blocking the grille. If so, maybe it's worth blocking a little less, so the energy to run the fan doesn't have to be used.
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Old 06-16-2008, 11:54 AM   #17
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Originally Posted by monroe74 View Post
In my own situation, I found it was very helpful to use a temporary setup for a couple of weeks. I feel like that taught me a lot about how my engine was operating. Then I felt there was no need for a permanent installation.
I too found that a temporary setup is good enough. A couple weeks usage and I don't need it again until I try some modificatons, though I use it sometimes anyway. I wouldn't mind permanently having a small gauge, maybe an LED bar graph or something.
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Old 06-17-2008, 08:09 AM   #18
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Wouldn't you need to take RPM into account? And fuel pressure?
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Old 06-17-2008, 09:22 AM   #19
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You definitely don't need to worry about RPM. You're measuring fuel per time (GPH), not fuel per revolution when you measure fuel injector duty cycle. If the fuel injector is open for 30 seconds out of every minute, that's 50% duty cycle, and it's feeding the same amount of fuel whether you're at 500 or 5000 rpm.

It's my understanding that in most systems, fuel rail pressure is the same under all conditions. If not then it could explain the observations I've made about WOT in my VW better than my guesses.
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Old 06-17-2008, 10:22 AM   #20
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I basically agree with what you said, but I want to add some details.

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You definitely don't need to worry about RPM. You're measuring fuel per time (GPH), not fuel per revolution when you measure fuel injector duty cycle. If the fuel injector is open for 30 seconds out of every minute, that's 50% duty cycle, and it's feeding the same amount of fuel whether you're at 500 or 5000 rpm.
There's another subtle issue, which has to do with injector latency. That means the injector doesn't open the exact instant the ECU asks it to. This is on account of inertia (magnetic and mechanical). Injector latency is the reason that injector specs cite a dynamic flow rate as well as a static flow rate. The latter means what would happen if the injector were open permanently. The former means what happens in the real world, with the injector opening and closing all the time, and therefore injector latency has an effect on the flow.

This ends up also having a relationship with RPM. Because of injector latency, a series of short pulses will emit less gasoline, as compared with one long pulse, even if the overall pulse width adds up to the same total. Theoretically what you really want to do is subtract a small amount of time from each separate pulse. And this is something the SuperMID does, for example.

Having said all that, I think it's probably a minor factor, in the context of what's being discussed here. But it might be good to realize that a 10% (let's say) duty cycle in top gear probably represents a little more gas than the same duty cycle in a lower gear. Because in top gear, that duty cycle is composed of a relatively small number of relatively long pulses. Therefore injector latency has less of an effect. Injector latency has more of an effect when each pulse is relatively short.

Quote:
It's my understanding that in most systems, fuel rail pressure is the same under all conditions.
I just want to add another clarification to this. My understanding is that most or all EFI systems use a fuel pressure regulator, to hold fuel pressure constant. But it might be helpful to understand that fuel pressure is held constant relative to manifold pressure, not relative to atmospheric pressure. This simply means that the pressure differential across the injector is held constant. The result is that a given pulse duration will always pass a constant amount of fuel. (This is also a bit of an oversimplification, since fuel density changes relative to temperature. But we can probably assume that engine operating temperature is relatively constant, which means we can ignore this factor.) And that's exactly what's wanted, both from the perspective of an engine designer/tuner, and from the perspective of someone who wants to measure fuel flow.
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