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Old 05-13-2008, 06:09 PM   #21
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"Sounds like you know a bunch of stuff I want to know"

Great. Just ask. I'm also learning some things from you.

"What is 'dwell' "

Before the existence of modern electronic ignition (found on all cars today), ignition systems used to use points (a kind of mechanical switch). They would open and close rapidly, as the distributor spun. They would cause the plugs to fire. It was important to adjust how long the points were closed (as compared with the time they spent being open). Because this had to do with rotation, the name given to this concept was "dwell angle" or "dwell time." It basically means the points are closed a certain percentage of the time, and open the rest of the time.

More stuff about this here: http://www.jetav8r.com/Vision/Ignition/CDI.html

It turns out that this concept (something being in one state a certain percentage of the time, and being in another state the rest of the time) has a general name: duty cycle (see here: http://en.wikipedia.org/wiki/Duty_cycle).

It also turns out that the concept of duty cycle is a very important part of how modern EFI works. Each injector is open a certain percentage of the time, and closed the rest of the time. (This is called either duty cycle or pulse width.)

If you can observe your injectors' duty cycle (or pulse width), you are essentially monitoring instantaneous fuel use.

You can buy a fancy automotive multimeter, which has a special feature called "duty cycle" or "pulse width," that is mostly intended to monitor injectors (although it also has other applications).

But you don't need a fancy automotive multimeter. You just need an automotive multimeter that has a "dwell" feature. Why? Because "dwell" is really just another term for "duty cycle."

So it turns out that a concept (duty cycle) that used to apply with regard to ignition (points and plugs) is now being applied with regard to fuel (EFI injectors).

The term "dwell" is archaic, because cars don't have points anymore. But it's really just another name for "duty cycle," so you can use a dwell meter to monitor your injectors.

If you look around a place like eBay, you'll find lots of dwell meters, cheap. They are often called "tach/dwell meters" because they also do tach. They are typically old and analog, but I think they would probably work sort of OK, for this purpose. But I was happy to find a cheap new DMM with a dwell feature.

Actually, the digital dwell is much better. That's because your injector duty cycle % is often very low (a number less than 10, on a scale of 90). This small value could be hard to read on an analog meter, especially if you want precision. Whereas on a DMM, no problem. Also, the DMM responds much faster than a mechanical needle.

"links to HF for the DMM and timing light? I think I found them"

Yes, you did. I decided I didn't need the fancy timing light.

If someone wants a DMM and doesn't need dwell, HF has them as low as $4! Amazing place.

"I'll be right near a HF store on Friday"

I've never been in one of their stores, but I just found out there's one not too far, so I intend to visit.

"spend money I don't have on stuff I don't need"

I can relate.

"Anyway, can you provide hookup details"

I could be very specific if you had a Honda. You don't, but I think the general principles still apply.

"What and where do I probe to read injector duty cycle?"

My ECU has 4 pins, one for each injector. I just picked one. Positive lead of DMM attaches here. Other lead of DMM attaches to chassis ground.

"What setting do I use on the DMM?"

A dwell meter has choices for number of cylinders (3,4,6,8). It almost doesn't matter what you choose. You should get a precise and meaningful result, at least in relative terms, even if you pick the wrong scale.

I set mine to 4 cylinder. That means full scale is 90 degrees (a quarter of 360). When you're in the world of dwell, you're speaking degrees of rotation.

When my dwell meter indicates 10, let's say, it thinks it's telling me that my points are open 10 degrees out of each 90. But here's what it's really telling me: my injectors are open 10/90th of the time.

90 degrees just happens to be a number that's conveniently close to 100 per cent. So when my meter tells me 10, instead of thinking "10 degrees," I just think "10 per cent." Easy.

If I set the meter for six cylinders, then full scale would mean 60, instead of 90. Because on a 6-cylinder engine, a cycle for the points (for one cylinder) is 60 degrees of rotation, instead of 90 degrees.

But understanding this part isn't that important. Even if you picked the wrong dwell scale, you would still see the numbers rise and fall, in a very precise way, as you manipulated the throttle. And you would figure out how to translate those numbers into more meaningful units (like gallons per hour).

"Where is a good place to probe the o2 sensor?"

If you don't have a wideband sensor (I think you don't; do you?), you might find that reading the sensor is not terribly interesting or helpful. Anyway, to find the answer to your question you could consult a shop manual or wiring diagram to understand which ECU pins are attached to the sensor.

"What setting do I use on the DMM?"

With the O2 sensor, it's simple DC voltage. You have several scales to choose from. You probably want something like a 2V scale.

"I have a Ross Tech Vag-Com"

That's interesting. Never saw that before. Thanks for mentioning it.

"I think they make similar products for non-VW cars too"

Their web site says only VW/Audi.

"maybe it would work on a plain OBDII"

My car is OBD1.

"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?"

Yes. That would be the concept. You would hopefully just need some simple instructions about how to hook it up.

Did you get the Vag-Com specifically because you liked the idea of getting this kind of data onto your PC?
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Old 05-13-2008, 06:33 PM   #22
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Hmmmm have to get digging through my old magazines...

http://www.nleindex.com/index.php?pI...dex&tID=E/4157
http://www.4qdtec.com/Automob/TachDwell.html
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Old 05-13-2008, 06:33 PM   #23
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Slightly off the topic, but...

I was playing with a co-workers 1999 Dodge truck a while back. I knew that with the '80s Mopars you could get the trouble codes by turning the ignition on and off three times. I tried it with the '99...got the trouble codes to read out through the odometer. (She was having issues with the EGR at the time.) Wonder how many other OBD II cars can access the codes in a similar manner?


Regarding the Cad...I love all the realtime data I can get...plus the ability to reset the "Service Soon/Service Now" lights. Most of the sensors have rather dodgy wiring...the car was a home for rodents for a few years, I think (there are still little poops all over the intake manifold!)
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Originally Posted by theholycow View Post
Would a light emitting diode do the job?



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 05-13-2008, 06:38 PM   #24
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Originally Posted by monroe74 View Post
Great. Just ask. I'm also learning some things from you.
Thank you for all the data.

Quote:
If someone wants a DMM and doesn't need dwell, HF has them as low as $4! Amazing place.
They often discount them to $3. Great place, I love it. Many/most of the tools are cheezy chinese knockoffs, but they get the job done and I would have none of them if not for HF. I was ecstatic when they finally put up a store in my state.

A similar company is Cummins Tools. They don't have as many stores, but they have a traveling sale, which comes to my small town once or twice a year.

Quote:
My ECU has 4 pins, one for each injector. I just picked one. Positive lead of DMM attaches here. Other lead of DMM attaches to chassis ground.
Cool. I can probably extend this wire to a convenient place on my dash and probe the extension. Then I can buy one $30 meter and use it in both vehicles.

Quote:
If you don't have a wideband sensor (I think you don't; do you?)
I thought they were common on newer vehicles, but maybe one or both of my vehicles have narrowband. I'm very interested in open/closed loop detection, especially in my VW.

Quote:
Their web site says only VW/Audi.
Yeah, I checked and that's what it looks like. However, while using the software it seemed like it would do some of its stuff for standard OBDII. Probably not.

Quote:
Did you get the Vag-Com specifically because you liked the idea of getting this kind of data onto your PC?
Not at all. In fact, until I had it, the idea hadn't even occured to me as being worthwhile, because I had planned to eventually get a ScanGauge II. I hadn't planned to get a Vag-Com at all due to the expense, but then I realized if I just got someone to commit to buying it from me then I could essentially rent it by buying it and then re-selling it. The only reason I wanted it was to change these programmable behaviors:
- One press of "unlock" on the remote unlocks both doors and the hatch
- Locking it doesn't make the horn go "beep"
- When I shut the car off everything unlocks
- I can open and close the windows using the remote (from long distances, even)
- The rear wiper doesn't come on automatically when I shift into reverse with the front wipers on (at least, I think it won't now)
- The rear wiper won't do the delayed cleanup wipe after I shut it off
- Seatbelt chime partially disabled (sometimes I start the engine first, THEN buckle my seatbelt before driving away)
- Some others that I don't remember
Also I needed it to clear a VW airbag code that my $40 HF standard OBDII scanner wouldn't clear.

The programmability of the 2006+ VW MkV platform is very cool. You can adjust a lot more things, even mechanical things (like steering effort, for example) but I didn't bother as I don't know how to adjust anything that I care to change.

Anyway, once I had it I decided I'd take it on a few data collection runs, and gather data for my daily commute. I want to know how gas pedal position affects throttle opening with the drive-by-wire system, and how my low RPM / heavy foot strategy affects air/fuel ratio, fuel flow rate, and such. I especially want to know when I'm in DFCO and when I'm not. I'm pretty sure it's all the way down to 990rpm but I think there's some lag in some cases.
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Old 05-13-2008, 06:44 PM   #25
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Originally Posted by JoeBob View Post
I knew that with the '80s Mopars you could get the trouble codes by turning the ignition on and off three times. I tried it with the '99...got the trouble codes to read out through the odometer. Wonder how many other OBD II cars can access the codes in a similar manner?

Most of the sensors have rather dodgy wiring...the car was a home for rodents for a few years, I think (there are still little poops all over the intake manifold!)
The procedure was similar for lots of 80s vehicles, which usually reported codes by flashing the dash backlight IIRC. However, for some such vehicles, a proprietary scan tool is now $25 at the nearest chain auto store.

A basic OBDII scanner is $30-40 at Harbor Freight now, worth it considering how many vehicles it will work on.

I have a major rodent problem with anything outdoors where I live, backed up to a state forest. The damned things have been destroying everything and I'm tired of it. I recently put out poison...
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Old 05-13-2008, 06:48 PM   #26
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AH Finally! someone who thinks like us...
http://www.ggimages.com/rx7/pwm.html
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Old 05-13-2008, 06:50 PM   #27
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I can send you some cats....

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Originally Posted by theholycow View Post

I have a major rodent problem with anything outdoors where I live, backed up to a state forest. The damned things have been destroying everything and I'm tired of it. I recently put out poison...
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Old 05-13-2008, 06:52 PM   #28
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I can send you some cats....
lol I've got two of 'em, don't let them outside.

Plus, the Buick has a cat that I'll be removing...
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Old 05-13-2008, 06:58 PM   #29
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AH Finally! someone who thinks like us...
http://www.ggimages.com/rx7/pwm.html
Keep it up, love the links you're coming up with! That one may be too difficult (especially when you can get that DMM from HF for $33 to do the job) but this one from the same site, I like:
http://www.ggimages.com/rx7/afmon.html

He's got a few cool links, actually...take a look at the list at
http://www.ggimages.com/rx7/rx7.html
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Old 05-13-2008, 07:45 PM   #30
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Originally Posted by RoadWarrior View Post
Just wondering if a regular AC voltmeter would work....
It's hard to say, I might hook up my DMM across one of my injectors and take a look when I get a little time to play.. I don't think I have an analog voltmeter any more.. I'll have to take a look in my junk box..

FWIW, an LED does indeed respond to pulse width as long as the current is kept quite low, a 5K ohm series current limiting resistor and a schottky diode would do the trick.

The circuit would look like this...

Injector positive---->LED--->5K resistor--->schottky diode--->injector ground.

A regular diode would probably work just fine but a schottky diode is high speed and might respond to narrow pulse widths better.

You could pick up everything at Rat Shack for less than $5..

I would get 2K, 5K, 10K and 20K resistors and see which one gives the best brightness variation.. Or just use a variable resistor and play with the settings ..
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