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Old 05-31-2002, 02:41 PM   #1
mynew02
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Default A/F with Delta Dash

I'm still wondering how acurate we can get with the A/F on the delta dash.

This was the most informative post on the subject:

Quote:
Originally posted by Jon [in CT]
To me, the wideband A/F ratio sensor data reveals alot.

First, the resistance of the A/F sensor is inversely correlated with its temperature. You can see how the resistance falls as the run progresses. This indicates rising EGT.

Second, the current (reported in mA) is positively correlated with the A/F ratio. Here's a little cheat sheet with A/F ratio in the first column and current in the second:
18:1 +7
16:1 +3
14.5:1 +0
14:1 -2
13:1 -6
12:1 -11
I would not put any faith in the reading when the current drops below -11.

Third, the number reported simply as A/F sensor #1 (the third set of A/F measurement) appear to be lambda values. Lambda is defined as measured A/F ratio divided by stoichiometric ratio. To convert a lambda value to an air/fuel ratio, just multiply it by 14.5 (or whatever your fuel's stoichiometric A/F ratio is.
The A/F sensor #1 data seems to flatline. I see more detail in the in my graphs of A/F current than A/F sensor #1. Notice the comparison on one of Jorge's graphs:



So is there an easy way to convert current into an A/F ratio?

-Jonathan
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Old 05-31-2002, 03:01 PM   #2
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Is there any sort of direct correlation? What is the ratio when A/F Sensor #1 > 0.76 ?

I think the question is the accuracy of the gauge, however. If it's not accurate, then the current values are just as useless. And if it IS accurate, wouldn't the ECU be using those values instead of the direct Sensor values? Or is sensor a computation by DD of the current and other things?
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Old 05-31-2002, 03:04 PM   #3
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You got me... dunno

I was hoping Jon[CT] would see this and comment... I haven't been logging A/F sensor #1 so I don't have any data with both sensors logged to allow me to look for the correlation. Jorge's server appears to be down so I can't grab any data from there with both values.

-Jonathan
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Old 05-31-2002, 03:09 PM   #4
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Edit: NM didn't fully read the first quote.

Can you get some exact measurements on A/F Sensor #1 and A/F current?

Last edited by gryphon; 05-31-2002 at 03:15 PM.
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Old 05-31-2002, 04:07 PM   #5
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From earlier posts, I recall that Jon stated the a/f sensor #1 shows a/f ratio. To calculate, you multiply the number by 14.5. Since the sensor #1 will not go below .76, this will not work for any ratio below 11:1. For this reason, I look at the a/f sensor #1 current to see how close I am getting to 11:1. With the little tuning I have done, it appears that your car goes to about 9:1 after an ecu reset. Once adjusted, you get around 10-10.5:1 which is mid to low 14's on the sensor current. I believe a sensor current of 13 from my experience is very close to 11:1 (below 13, your sensor #1 will move off of .76).

As for accuracy of the sensor # 1, Jorge stated that it was very close to his greddy a/f gauge. Hopefully, he can comment on this. With txs now selling this product, they can hopefully compare the sensor current readings with a wideband and report to use on their findings. That would be very helpful.

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Old 05-31-2002, 06:43 PM   #6
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There was another thread on a similar subject:
http://www.i-club.com/forums/showthr...hreadid=183070

I can give you a formula that'll convert Air Fuel Sensor #1 Current (AFS1C) to lambda, BUT ONLY FOR CURRENT VALUES GREATER THAN -12 MILLIAMPS:
Code:
+(.99910894+(.032800617*H2)+(.0021423261*H2*H2)+(8.2261549E-05*H2*H2*H2))
In this formula, H2 is the cell that contains an AFS1C value.

If you plug the value -12 into that formula as H2, you'll calculate a lambda of 0.77, which you could also get by looking at Air Fuel Sensor #1 (AFS1). So that formula isn't all that useful if your DeltaDash is collecting AFS1. For values less than -12, AFS1 will report a lambda of 0.76 which appears to be the lowest value the sensor controller subsystem will ever report to the main ECU, regardless of how low below -12 the sensor current falls.

When the current falls deeper than -12 into negative territory, the relationship between it and lambda changes. Here's a graph which shows how I think the current behaves in this area:

As the sensor saturates in very rich mixtures, the sensor's response loses it linearity and progressively smaller changes in sensor current represent larger changes in lambda.
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Old 05-31-2002, 07:15 PM   #7
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There may be another issue as well. When I was dyno tuning, I saw no difference in a/f current between <9:1 and 11:1, as measured by the delta dash. The sensor may still be changing current, in the nonlinear region, but the electronics in the ECU may have saturated and is not reporting the true sensor current. The only way around this is to break the sensor current lead, insert a very low resistance current measuring shunt, and read the sensor current directly. Gotta go - thunderstorm!!

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Old 05-31-2002, 08:07 PM   #8
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fastburro, are you sure? I looked at two of your DeltaDash logs and your Air Fuel Sensor #1 Current was ranging from -12.25 down to a low of -16 milliamps during the period that A/F ratios were less than 11:1. Maybe you were looking at Air Fuel Sensor #1, which sits at 0.76 whenever A/F ratios go below 11:1.
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Old 05-31-2002, 08:36 PM   #9
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I don't understand this...

When I got tuned at TXS their A/F meter showed me to be above 11:1 for the majority of my run in 4th gear. When I log with DD I peg .76 almost the entire time.

Granted I'm not more than 11.2:1 but I should be over 11:1 from 5000-7000 rpms.

-Jonathan
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Old 05-31-2002, 09:22 PM   #10
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Quote:
Originally posted by mynew02
I don't understand this...

When I got tuned at TXS their A/F meter showed me to be above 11:1 for the majority of my run in 4th gear. When I log with DD I peg .76 almost the entire time.

Granted I'm not more than 11.2:1 but I should be over 11:1 from 5000-7000 rpms.

-Jonathan
It sounds like you're making an argument for using 14.7:1 as the stoichiometric ratio for the gasoline you were using, instead of the 14.5:1 that I have proposed. Because if you gasoline's lambda=1 A/F ratio WERE 14.7:1, then .76*14.7=11.17 .

Actually, TXS's A/F meter was probably setup to presume that your gasoline's stoichiometric ratio was 14.7:1. Presumably, they could have programmed in some other value. If they had used 14.5:1, then you would have seen ratios on their meter of less than 11:1 when the DeltaDash said .76.

Don't forget that the WRX's A/F sensor signal (and that of all automotive O2 sensors) is always relative to the fuel's stoichiometric ratio. For instance, if you were to use straight methanol as the fuel in your WRX, then DeltaDash's Air Fuel Sensor #1 would report a value of 1.00 whenever the air/fuel ratio was around 6.4:1, which is methanol's stoichiometric ratio.

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Old 05-31-2002, 09:35 PM   #11
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Jon, do you have any links to show how to Bosch sensor inputs and outputs this information? In other words... how it knows the current output to produce?
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Old 05-31-2002, 10:05 PM   #12
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Quote:
Originally posted by gryphon
Jon, do you have any links to show how to Bosch sensor inputs and outputs this information? In other words... how it knows the current output to produce?
I do, but the WRX's front A/F sensor is produced by Denso and is unique in that it relies on a limit current to signal the lambda, instead of a pump current which Bosch and NTK wideband sensors rely upon.

I want to reinforce the fact that Air/Fuel Ratio sensors and O2 sensors are actually responding to Lambda values and not ratio values. Attached below is a snippet from the FJO Wideband Sensor Controller manual (FJO happens to use an NTK wideband sensor). Their controller is obviously pre-programmed for stoichiometric=14.7:1, the typical ratio given for gasoline. If you read up from the horizontal axis at 14.7 to the violet methanol line and then read over to the vertical axis to find the true methanol A/F ratio, it turns out to be ~6.4.
Attached Images
File Type: gif alternatefuellambdas.gif (36.1 KB, 251 views)
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Old 06-01-2002, 12:46 AM   #13
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Quote:
Originally posted by Jon [in CT]
fastburro, are you sure? I looked at two of your DeltaDash logs and your Air Fuel Sensor #1 Current was ranging from -12.25 down to a low of -16 milliamps during the period that A/F ratios were less than 11:1. Maybe you were looking at Air Fuel Sensor #1, which sits at 0.76 whenever A/F ratios go below 11:1.
I believe so, Jon. When we first started doing the runs, the dyno a/f was seriously below 10:1, and I'm pretty sure the DD was reading the same current(flatline) then as it was when we got the a/f up to about 11:1 on the dyno sensor. I'll check my logs more carefully, but that was my impression when we were taking the data. I'm certain that I wasn't looking at the voltage, as I was most interested in what the raw current from the sensor was doing.

Mark
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Old 06-04-2002, 12:07 AM   #14
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OK.. I've posted my concern before in a 'round about way but here it is again...

We know the DD (A/F Sensor #1) supposedly flatlines at 11:1 A/F ratio. How do you explain the fact that on my most recent dyno run at TXS I was only below 11:1 from 4700 rpm to 5100 rpm (that's for about 400rpm) yet my delta dash shows me hitting flatline (supposedly 11:1 or below) from 2700 rpm to redline (almost the entire run.)

I want to add some supporting info. The only mod I've made since the dyno run is the elimination of the cat. Do you think that could have caused the ECU to overcompensate and richen me that much? We also know that if my ECU was pulling timing or possibly reset that would make me go rich but I'm logging these results even on runs with great timing.

Just wanted some opinions... and the reason I'm posting this is because if people are using s-afc's to lean out their mix and the delta dash is actually flatlining at A/F's above 11:1 people may be running quite lean and not realize it. I think I need to make another run on the dyno WHILE logging for comparison.

-Jonathan
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Old 06-04-2002, 10:48 AM   #15
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Jonathan, I really don't know but I would think removing the cat is going to cause a leaner mixture (very slight). It might be just enough to show up. Look at your a/f learning. Has it changed since your run at txs? If so, the ecu has changed the a/f on you. I might also suggest running at different boost levels can change a/f but I would think on your unichip this should not matter at the boost levels you are running. However, if you go below 13.5psi it could.

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Old 06-04-2002, 11:21 AM   #16
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Exhaust A/F sensors respond to Lambda (λ) which is the relative A/F ratio and is defined as actual A/F ratio divided by stoichiometric ratio. So, in order to convert the response from an A/F sensor to an A/F ratio, you need to first specify the fuel's stoichiometric ratio. High end (lab grade) A/F meters allow you to specify the fuel's actual proportions (relative to weight) of oxygen, hydrogen and carbon and can then calculate the fuel's stoichiometric ratio by assuming dry air consisting of 20.95 percent oxygen. Lesser meters allow you to simply input your estimate of the fuel's stoichiometric ratio. And, at the low end of wideband meters, the manufacturer (such as FJO, above) preprogram a stoichiometric ratio into the meter.

So, what stoichiometric ratio should be used to convert DeltaDash's Air Fuel Sensor #1 lambda value to an air/fuel ratio? Denso engineers seem to prefer 14.5:1. I say this for two reasons. The SAE paper which describes how the Denso A/F sensor works (SAE 970843) uses 14.5:1 throughout. And the DeltaDash Air Fuel Sensor #1 limit values seem to be .76 and 1.72 which when multiplied by 14.5 result in values that are too close to the round values 11:1 and 25:1 to be coincidence. On the other hand John B. Heywood's Internal Combustion Engine Fundamentals gives the stoichiometric ratio for gasoline as 14.6:1 in Appendix Table D.4. The Bosch Automotive Handbook offers 14.6:1 for premium gas and 14.7:1 for regular gas. By far, though, the most commonly cited value for gasoline is 14.7:1.

If you want to compare the DeltaDash Air Fuel sensor #1 values to those A/F ratios reported by some wideband meter at the dyno, you need to know what ratio the meter considers to be stoichiometric. If the operator doesn't know, then assume it's 14.7:1. An even better method would be to try and see what the dyno's A/F meter says when DeltaDash's Air Fuel Sensor #1 is reporting 1.0 and use whatever that ratio to convert DeltaDash Lambda values to A/F ratios.
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Old 06-04-2002, 11:22 AM   #17
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Quote:
Originally posted by TurboRex
Jonathan, I really don't know but I would think removing the cat is going to cause a leaner mixture (very slight). It might be just enough to show up. Look at your a/f learning. Has it changed since your run at txs? If so, the ecu has changed the a/f on you. I might also suggest running at different boost levels can change a/f but I would think on your unichip this should not matter at the boost levels you are running. However, if you go below 13.5psi it could.

Greg
Thanks for your input... I didn't have the DD when I went to TXS last so I didn't have a baseline. I agree that you would think it would make you leaner but as with many mods our ECU picks up on the better flow and over-corrects for it by dumping too much fuel. Now I'm not saying that is happening only that if the DD is correct and flatlines at 11.1:1 that I am much richer now than I was when I was dynoed at TXS.

Again the other possibility is that the DD flatlines at mixtures leaner than 11:1 in which case tuning off of it could be a concern for those assuming that the flatline IS 11:1. I am trying to get more dyno time so I can put this to rest.

Jorge, you have an A/F guage. Are you seeing the DD as flatlining WHEN your A/F guage goes to 11:1 or does it flatline before your guage reads 11:1?

-Jonathan
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Old 06-04-2002, 11:54 AM   #18
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Quote:
Originally posted by Jon [in CT]
Exhaust A/F sensors respond to Lambda (λ) which is the relative A/F ratio and is defined as actual A/F ratio divided by stoichiometric ratio. So, in order to convert the response from an A/F sensor to an A/F ratio, you need to first specify the fuel's stoichiometric ratio. High end (lab grade) A/F meters allow you to specify the fuel's actual proportions (relative to weight) of oxygen, hydrogen and carbon and can then calculate the fuel's stoichiometric ratio by assuming dry air consisting of 20.95 percent oxygen. Lesser meters allow you to simply input your estimate of the fuel's stoichiometric ratio. And, at the low end of wideband meters, the manufacturer (such as FJO, above) preprogram a stoichiometric ratio into the meter.

So, what stoichiometric ratio should be used to convert DeltaDash's Air Fuel Sensor #1 lambda value to an air/fuel ratio? Denso engineers seem to prefer 14.5:1. I say this for two reasons. The SAE paper which describes how the Denso A/F sensor works (SAE 970843) uses 14.5:1 throughout. And the DeltaDash Air Fuel Sensor #1 limit values seem to be .76 and 1.72 which when multiplied by 14.5 result in values that are too close to the round values 11:1 and 25:1 to be coincidence. On the other hand John B. Heywood's Internal Combustion Engine Fundamentals gives the stoichiometric ratio for gasoline as 14.6:1 in Appendix Table D.4. The Bosch Automotive Handbook offers 14.6:1 for premium gas and 14.7:1 for regular gas. By far, though, the most commonly cited value for gasoline is 14.7:1.

If you want to compare the DeltaDash Air Fuel sensor #1 values to those A/F ratios reported by some wideband meter at the dyno, you need to know what ratio the meter considers to be stoichiometric. If the operator doesn't know, then assume it's 14.7:1. An even better method would be to try and see what the dyno's A/F meter says when DeltaDash's Air Fuel Sensor #1 is reporting 1.0 and use whatever that ratio to convert DeltaDash Lambda values to A/F ratios.
Ok Jon... thanks for the technical reply.

I think I have what your saying... the factory 02 probably needs a ratio of 14.5 to get A/F while the TXS wideband 02 may be using the ratio 14.7.

If that is the case it would result in only a slight difference though. The DD would flatline at 11.1 (@ the 14.5 ratio) and would equal the TXS reading of 11.2 (@ the 14.7 ratio) Hmmm... I'll go back and check my data to see if this matches up.

Thanks! I'll report my findings.

-Jonathan

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Old 06-04-2002, 12:02 PM   #19
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Ok... here is the comparison (keep in mind the DD is with no cats and the dyno plot is with TXS hi-flow cat.)





OK... lets assume that 11.2:1 on the TXS graph = 11.1:1 (after ratio of 14.5 is used) on the DD. On the TXS graph I'm at 11.2:1 or richer from 4500 through redline (look at the pink line.) In my DD chart I'm flatlining from about 2700-redline. In the TXS chart I'm at 12.8:1 at 2700. That means the two are reading very different still even if assuming that the ratios between the factory 02 and the TXS 02 are different (14.5 vs. 14.7.) Hmmm.. maybe it's the absence of cat making me run more rich (ecu over correcting for added flow.)

-Jonathan

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Old 06-04-2002, 12:06 PM   #20
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Quote:
Originally posted by mynew02
I think I have what your saying... the factory 02 is probably reading 14.5 while the TXS wideband 02 may be set at 14.7.
I don't think you do. Both the WRX and the wideband are reading lambda, not ratio. The TurboXS meter is reporting ratios, so that means it is multiplying the lambda values it is reading by some number that the designer considers a typical stoichiometric ratio for gasoline. You have to decide what that number is and then multiply your DeltaDash Air Fuel Sensor #1 values by it to get corresponding A/F ratios from your DeltaDash.
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Old 06-04-2002, 12:11 PM   #21
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Quote:
Originally posted by Jon [in CT]
I don't think you do. Both the WRX and the wideband are reading lambda, not ratio. The TurboXS meter is reporting ratios, so that means it is multiplying the lambda values it is reading by some number that the designer considers a typical stoichiometric ratio for gasoline. You have to decide what that number is and then multiply your DeltaDash Air Fuel Sensor #1 values by it to get corresponding A/F ratios from your DeltaDash.
Sure I think I understand... we don't know what TXS used for their ratio but we think the WRX lambda should use a ratio of 14.5 to get A/F. I am making an assumption that TXS is using 14.7 so I ran the comparo above... and even given this possibility things didn't match up.

Looking back at my explanation above I see why you didn't think i understood I'll change that thread

-Jonathan

P.S. Sorry I'm nitpicking this to death. I'm just trying to use what data I have to see how reliable the DD is for tuning (of course above the 11.1:1 ratio that we CAN see.)

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Old 06-04-2002, 12:29 PM   #22
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I just changed my wording on my last three posts above so re-read if you are trying to get any meaning from them

How about this possibility... The factory 02 is up front and the 02 TXS uses is in the tailpipe. Could readings be leaner at the tail than they are up front in the manifold?

-Jonathan
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Old 06-04-2002, 12:31 PM   #23
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Quote:
Originally posted by mynew02
OK... lets assume that 11.2:1 on the TXS graph = 11.1 on the DD. I'm at 11.2:1 or richer from 4500 through redline (look at the pink line.) In my DD chart I'm flatlining from about 2700-redline. In the TXS chart I'm at 12.8:1 at that point. Hmmm.. maybe it's the absence of cat?
First, the presence or absence of cats has no effect on the lambda measured by the WRX's front A/F sensor, However, it may have a brief effect on a dyno's A/F meter if the meter's sensor were inserted into the muffler. As you go to wide-open throttle and very rich, the oxygen stored in the catalytic converters is released and would, for a short time until it's all gone, make the exhaust appear leaner to a downstream sensor than it really was when exiting the combustion chambers.

If 14.7 is considered stoichiometric by the dyno's A/F meter, then 14.7*.0.76=11.2.

These graphs aren't useful to me. I see three dyno A/F lines, none of which were measured during the DeltaDash run. And DeltaDash graphs are generally worthless to me when actual values are possible.

If you do decide to try and correlate DeltaDash to a dyno's A/F meter in a future dyno session, try collecting only RPM, Air Fuel Sensor #1 and Air Fuel Sensor #1 Current from DeltaDash to get the best possible data and resolution and try asking they dyno operator for a diskette containing the raw dyno A/F meter data (not just the graph).

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Old 06-04-2002, 12:54 PM   #24
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Quote:
Originally posted by Jon [in CT]
First, the presence or absence of cats has no effect on the lambda measured by the WRX's front A/F sensor, However, it may have a brief effect on a dyno's A/F meter if the meter's sensor were inserted into the muffler. As you go to wide-open throttle and very rich, the oxygen stored in the catalytic converters is released and would, for a short time until it's all gone, make the exhaust appear leaner to a downstream sensor than it really was when exiting the combustion chambers.

If 14.7 is considered stoichiometric by the dyno's A/F meter, then 14.7*.0.76=11.2.

These graphs aren't useful to me. I see three dyno A/F lines, none of which were measured during the DeltaDash run. And DeltaDash graphs are generally worthless to me when actual values are possible.

If you do decide to try and correlate DeltaDash to a dyno's A/F meter in a future dyno session, try collecting only RPM, Air Fuel Sensor #1 and Air Fuel Sensor #1 Current from DeltaDash to get the best possible data and resolution and try asking they dyno operator for a diskette containing the raw dyno A/F meter data (not just the graph).
Thanks again for the info...

I am not really trying to compare the curves (there's virtually no curve with the DD as it seems to be below 11.1:1 nearly the entire run.) I am only looking at the point at which the curves pass the DD's flatline point (.76 or 11.1:1.)

What you say about the cat makes sence and could explain why the DD dips below the calculated 11.1:1 threshold sooner. I was pointing out that the added flow by removing the cat could also have propted the ECU to over-correct and dump more fuel earlier.

Bottom line is we need a side-by-side comparison of the same run to prove anything and that's what I am going to get...

If anyone else out there has the Delta Dash please hook it up if you get on the dyno and see how the comparison of A/F looks to the wideband 02 used on the dyno. This way we can feel comfortable using the DD to tune.

-Jonathan
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Old 06-05-2002, 12:35 AM   #25
Conduit
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This is interesting. As I read what is going on here, something struck me. One of the biggest complaints I hear from tuners of all levels using piggyback anythings is that timing is a real pain. The values are changing, etc. by the ECU and it's tough to map consistently. Is it possible that the core problem is simply that the ECU can't distinguish below 11:1, so it does certain things to fuel and ignition based on knock input to swing things back to higher ratios, thus temporarily changing the base ignition value via trim in an unexpected way? Again, I am trying to discover how to layer the piggyback around it, and perhaps if we knew more about how the ECU uses the A/F and EGT sensors, we could accomplish that.
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