After race day at Hagarstown, my energy for doing actual work on the Dart had lost some of it's umph. Until one evening, when my wife sys, "The Dart doesn't start very well does it?"

"What are you talking about, it starts every time", I reply. Humph.

"Yeah, but takes 3 or 4 tries", she says.

"Only when it's cold", I respond.

I could tell that was not good enough by the ensuing silence. Hmmm. Maybe I should spend a little time tuning the cold start enrichment. The juices started to flow. I could feel my feet stirring so, I got up, gathered the lap top stuff, and went out into the garage to work on the problem. "Maybe she is right", I thought. "I should do something about this".

I raised the 80 degree ECT enrichment constant from 110 to 115,and bingo, the car started and idled fine. I proceeded to watch the screen and the narrow band O2 reading to see if the next cell warmer needed to be tweeked, and it suddenly dawned on me that even though limited, this tool was useful as a tuning aid replacement for my dead AF ratio gauge.

So, I watched as the engine heated up to the point where closed loop is engaged and the o2 readings start influencing the fueling mixture. Now, the present narrow band O2 sensor has a flawed bias, right out of the box. To get it to run at 14.8 in closed loop, I had to set the crossover voltage at .7 instead of .5. It ran lean when set at .5. So I watched the O2 voltage, and noticed that it was idling at .22 volts. That's pretty rich I thought. So I played with the fuel map a bit, and easily brought the O2 voltage up to .37 at idle. And, the car idled better. It seemed to respond better to the gas pedal as well. So, I am thinking, maybe this is what Lou has always been looking at when he sat over there tap, tap tapping on the computer keys while we drove around in tuning mode.

So, it is not real convenient, and Al, I do plan on getting the wide band gauge figured out, but in the mean time, what are the limits of this? It seems that if you can get the fuel map close enough, then very fine tuning is possible. You will not know exactly what AF ratio you are running, but then again, even with a wide band gauge, if the sensor is biased a little wrong, which has been the case with at least one new sensor in one of my new cars, then you might not be getting accurate information any way.

And a corollary to all this, some here seemed to think auto tune would work with a narrow band, only with limits. Anybody want to weigh in on this? And how do you get auto tune to work with megatune 2.25? Is it a seperate, stand alone program, or is there some automated way it dovetails with Mega tune 2.25?

Sam

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I've used the narrow band in open-loop, and use the following as a guide to what the AFR mixture is:


mV.... AFR

890.. 12.50
850.. 13.55
825.. 14.00
800.. 14.36
760.. 14.60
700.. 14.69
450.. 14.70
133.. 14.75
100.. 15.05
88.... 15.30
70.... 15.80
59.... 16.20
24.... 18.00

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Ems, I don't know what mV stands for. Help me out here. How do I use your chart? Thanks

Sam

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mV=milli volts??

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An officialis Tyrde-Browne Racing membrum

correct


890 = .89 volts

....

450 = .45 volts

....

70 = .07 volts


If you graph it, you'll get something like this:




bottom axis is lambda or AFR/stoic mixture (14.7 for gasoline)

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Thanks Guys, So my thinking was upside down. And I should have known it was. I just wasn't thinking it through. Here is the peculiar thing: as I clicked the number down in the VE table, thus making it leaner, the O2 sensor voltage went up. That does not compute as they say. This observation overrode what I KNEW to be the facts behind the case, namely that higher voltage is richer. The result was that when I glanced at your chart last night, it did not correlate to what I thought I had just experienced.

So something else was at play in making the numbers go up at that moment. I wonder what. I know the engine was not operating in closed loop at that rpm. I have it set to go into closed loop at 1300 RPM. In any event, it seems as if I can possibly use the narrow band sensor to do some tuning.

I can see from your chart why the narrow band sensor is hard to tune with. It jumps from almost perfect to very, very rich in just 100 mV. And conversely, relatively large jumps in readings on the lean side represent a small change in AF ratio. (See how smart you have made me now. . I can type mV and know what it means ) And my guess is the mixture bounces around too much to get a stable reading from the O2 sensor. As you pointed out, you would have to watch it in open loop so the correction didn't foul up your observations. As just an aside, why do you suppose there is such a sudden change in voltage with such a small change in AF ratio numbers.

So I have mostly ignored all tuning comments that talked in terms of lamba since actual AF ratio was a language I could translate more easily. And, that is the language my A/F meter spoke. Using the language of lambda, what are good workable ranges to shoot for? Is a lamda of .98 to 1.02 a decent range, or is this too wide, or too narrow? Are there any guidelines we can use that will lead us towards a more perfect AF ratio using lambda calculations? I ask because I am now going to try and use EMS chart as a guide to tune with. And, I will likely make a spread sheet chart of lambda numbers for the various mV readings.

Thanks again. And thinks for not making fun of my misunderstandings of the moment. I guess we all do that from time to time.

Here is my spread sheet chart based on EMS figures. See if I did this right please.

mv's.. AF ratio.. lambda
890... 12.50... 0.85
850... 13.55... 0.92
825... 14.00... 0.95
800... 14.36... 0.98
760... 14.60... 0.99
700... 14.69... 1.00
450... 14.70... 1.00
133... 14.75... 1.00
100... 15.05... 1.02
88..... 15.30... 1.04
70..... 15.80.. 1.07
59..... 16.20... 1.10
24..... 18.00... 1.22

Sam

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.98 to 1.02 sounds good.........


Lambda is good if you're using other fuels that don't have the correct mixture at 14.7.

You're probably not at 14.7 anyway, as I bet there's ethanol in the fuel....


The only way that going leaner would increase the mV is if the mixture was so rich that you got a rich-misfire. Since the fuel didn't burn, there was excess O2 in the exhaust and it looked lean........

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

How rich would it have to be for that to happen? When the wide band gauge was working, it was reading about 13.5:1 at idle. Would that be rich enough to cause the phenomenon you describe? Or would a rich misfire have caused the wide band to read leaner than it was. This gets tricky.

Sam

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A rich misfire would affect the wide-band the same way (reads leaner)

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

13.5 is not rich enough to cause a misfire - most engines will run quite happily at that AFR. You have to get into the 10's or richer on most engines to make it miss.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

But if it's in the 10's and there's a misfire, it might look like 13.5 because of all the O2 from the cylinder that misfired.........

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

However, I did tune down to 13.5 from 14.7 as it was running when I was setting up the fuel map. It seems unlikely that it would make a jump down to ten from 14.5. I could feel it going from lean, say 16:1 down to stoich. Do you think there is any possibility that it was still too rich, and looking lean at 16:1? It seems that the idle would improve as you pushed the AF ration numbers up from there if that were the case, and it got better as the numbers dropped,(richer).
Sam

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After reading this, nope I don't think it's too rich.

Sounds like you snuck up on it, and 13.5 is accurate.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes