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Old 05-12-2008, 06:47 PM   #11
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Back in the '70s vacuum gauges were sold which were calibrated as green, yellow, red...green meant you were getting good mileage, etc. Some mid-'60s Chevy Impalas came with a similar vacuum gauge installed right in the dashboard.

I just remembered...I used to have a bunch of Hot Rod magazines from the late '40s and early '50s...similar vacuum gauges were marketed even then.
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Old 05-12-2008, 06:53 PM   #12
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all obd1-obd2b hondas have saturated high-impedance injectors ~12ohms resistance
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Old 05-12-2008, 06:57 PM   #13
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Quote:
Originally Posted by fumesucker View Post
You would have to use a diode to keep current from the capacitor from flowing back into the injector when the capacitor had more charge than the injector drive circuit
Would a light emitting diode do the job?

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Originally Posted by JoeBob View Post
Many Cadillacs and Lincolns from the early '80s on have an MPG readout built in. My first one was in my '85 Continental...along with a digital gas gauge which read in gallons (you could watch the gas being sucked right out!). Same with my '84 Town Car, although you got a bar-graph fuel gauge. If you went into diagnostic mode, you could even see the fuel flow rate.
My 1987 Cadillac Deville had it too. In diagnostic mode you could get all kinds of sweet realtime data, though at the time I had it I didn't care about fuel flow rate. You could also get the trouble codes too. I wish modern vehicles came with that; you still have to pay hundreds of dollars for an OBDII scanner that will give you that amount of data (or at least $160 for a ScanGauge). A cheap one just gives you trouble codes.
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Old 05-12-2008, 06:59 PM   #14
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Would a light emitting diode do the job?
LED's don't like reverse voltages, so the answer is no..
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Old 05-12-2008, 08:24 PM   #15
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Quote:
Originally Posted by JoeBob View Post
Back in the '70s vacuum gauges were sold which were calibrated as green, yellow, red...green meant you were getting good mileage, etc. Some mid-'60s Chevy Impalas came with a similar vacuum gauge installed right in the dashboard.

I just remembered...I used to have a bunch of Hot Rod magazines from the late '40s and early '50s...similar vacuum gauges were marketed even then.
J.C. Whitney still sells one of those...
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Old 05-13-2008, 07:13 AM   #16
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Quote:
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You would have to use a diode to keep current from the capacitor from flowing back into the injector when the capacitor had more charge than the injector drive circuit
Good point.
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Old 05-13-2008, 07:44 AM   #17
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Just wondering if a regular AC voltmeter would work....
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Old 05-13-2008, 01:45 PM   #18
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"I would like to find a cheap fuel rate (GPH) meter"

Me too, so I got a DMM with a dwell feature.

"It occurred to me that you could wire up a LED indicator light (for example "green" for "go") in parallel with the fuel injector (so that the LED is run by the same signals that trigger the FE to use fuel)"

I don't think this will work, because the injector is controlled by pulse width, not increased/decreased voltage. In other words, I think you will just see a steady glow. The LED is not going to report pulse width.

"you could probably rig a voltmeter through a capacitor to give you injector pulse width duration"

I don't get how that would work. But you can get the info you're looking for if you get a DMM with a dwell feature. Some are expensive, but Harbor Freight has one for $33. For me that was a very good value, because it's a decent DMM, and it's also a tach, which I needed. It will also measure temperature, with a thermocouple (although I haven't tried that). And there's also the dwell feature.

I also bought their timing light for $11. Cheaply made and not very bright, but it worked fine, and is perfect for my occasional use.

I don't work for them. I'm just enjoying these bargains.

I'm using the DMM daily to monitor fuel flow rate (by reading injector duty cycle), and air/fuel mixture (by reading the output of the wideband O2 sensor on my VX). It works great (although I can't read both those values at the same time, of course). I'm learning a lot.

It was easy to set up, and I'd be glad to offer suggestions to anyone who needs tips on how to do it.
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Old 05-13-2008, 02:12 PM   #19
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Now that I've gotten started doing realtime monitoring on my OBD1 car, I'm thinking about taking it further.

I notice that it's possible to get a PC-based data-acquisition interface for as little as $25 (that's the RS-232 version; USB is $50). See here: http://www.dataq.com/194.htm

With 4 channels, and a laptop sitting in the car, I could do realtime data capture of all sorts of things. The most important data is fuel flow rate and vehicle speed. This would be enough to do all sorts of interesting mpg calculations. But I could also grab throttle angle, air/fuel mix, engine speed and/or engine temp, or other things.

It's hard to mount a laptop next to the speedo, but I could put it on the floor in front of the passenger seat. I could set it up so large numbers appear, so it would easy to glance at it. This is more-or-less how I currently use the DMM. (Or I could rig the kind of support cops use to mount a laptop they can see while driving.)

But the real payoff is that I'm capturing a mountain of data that I could analyze later, in various ways. And if I'm driving the same route every day, I could end up with a spreadsheet or similar program that lets me do careful comparisons of different driving strategies.

It seems to me that an approach like this would beat the pants off a Scangauge, in both features and cost. As far as I know, they still haven't delivered a PC interface. What I'm describing should be able to provide all the measurements provided by an SG, but in a way that captures the data for further analysis, which means you can get a lot more value out of the data the vehicle provides.

Another approach to this is to use a PDA (e.g., a Palm Pilot) instead of a laptop. Then it actually would be easy to mount the device where is can serve as a display while you're driving. While also capturing the data for later analysis and comparison.

As far as I can tell, this hasn't been done yet, because data acquisition systems, and computers to run them, used to be scarce and expensive. But that's not true anymore.

Anyway, I'm wondering if anyone here has tried anything like this, or heard or seen of anyone trying anything like this. And does anyone see reasons why this wouldn't work? I'm trying to think it through.
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Old 05-13-2008, 03:30 PM   #20
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Quote:
Originally Posted by monroe74 View Post
"I would like to find a cheap fuel rate (GPH) meter"

Me too, so I got a DMM with a dwell feature.

[...]get a DMM with a dwell feature. Some are expensive, but Harbor Freight has one for $33.[...]

I also bought their timing light for $11. Cheaply made and not very bright, but it worked fine, and is perfect for my occasional use.

I don't work for them. I'm just enjoying these bargains.

I'm using the DMM daily to monitor fuel flow rate (by reading injector duty cycle), and air/fuel mixture (by reading the output of the wideband O2 sensor on my VX). It works great (although I can't read both those values at the same time, of course). I'm learning a lot.

It was easy to set up, and I'd be glad to offer suggestions to anyone who needs tips on how to do it.
Wow! Sounds like you know a bunch of stuff I want to know.

What is "dwell", anyway?

Links to HF for the DMM and timing light? I think I found them:
DMM, $33: http://www.harborfreight.com/cpi/cta...emnumber=95670
Basic timing light, $13: http://www.harborfreight.com/cpi/cta...temnumber=3343
Deluxe timing light with advance, $30: http://www.harborfreight.com/cpi/cta...emnumber=40963

I'll be right near a HF store on Friday, and I was already planning to go there and spend money I don't have on stuff I don't need.

Anyway, can you provide hookup details for dummies?
- What and where do I probe to read injector duty cycle? What setting do I use on the DMM?
- Where is a good place to probe the o2 sensor? What setting do I use on the DMM?
- Any other suggestions and details?

Quote:
Anyway, I'm wondering if anyone here has tried anything like this, or heard or seen of anyone trying anything like this. And does anyone see reasons why this wouldn't work? I'm trying to think it through.
I have a Ross Tech Vag-Com for hooking my laptop to my VW, but I won't have it for long, and I'm not entirely satisfied with it anyway. It does a decent amount of logging, and can log at least 4 variables simultaneously. I just got it yesterday and it's broken already, but it seems like it would do what you want. I think they make similar products for non-VW cars too, or maybe it would work on a plain OBDII. Once it's fixed maybe I'll try it on my GMC. The problem is price; it's $250, though that's for the latest one that can do all kinds of cool stuff with a 2006-2008 VW.

The Dataq data acquisition kit doesn't look like something that can be figured out by someone like me, let alone people who are less technically inclined. Could it be done by non-techies with a DIY document?

On your PDA idea, I have a Garmin iQue 3600 PDA/GPS with a dash mount that I've always wanted to interface to OBDII...
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