If Tuning the VE table we remove the MAF then couldn't we....?
04-11-2005, 06:22 PM
#41
The oxygen sensor doesn't measure the oxygen/fuel ratio. It compares the percentage of oxygen in the ambient air to the percentage oxygen in the exhaust. That's why you can't cut your o2 wires and solder them, cause it has the reference air in it. So if there's 20% less oxygen in the air and 20% less oxygen in the exhaust too, the sensor should read the same if I understand correctly.
04-11-2005, 06:39 PM
#42
Originally Posted by P Mack
The oxygen sensor doesn't measure the oxygen/fuel ratio. It compares the percentage of oxygen in the ambient air to the percentage oxygen in the exhaust. That's why you can't cut your o2 wires and solder them, cause it has the reference air in it. So if there's 20% less oxygen in the air and 20% less oxygen in the exhaust too, the sensor should read the same if I understand correctly.
04-11-2005, 07:35 PM
#43
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Mass flow = (VE * MAP * RPM * Displacement) / IAT
which is derived from this equation:
VE = ((mass flow * IAT / (MAP * RPM * Displacement))
Were did you get your formula from?
If that is correct then I see a problem right of the bat. The IAT sensor is basically embedded in the plastic lid that as you know gets very hot and I'm 100% for sure that most of the time its reading is no were near actual intake air temp.
Next issue I have with that is doesn't installing a big cam change the MAP range of our motors? Shouldn't it lower the active range of the sensor? Wouldn't that invalidate the results of the equation?
You know if that equation is valid why couldn't we easily create an excel sheet that would take the Data Logs and do the calculations and then associate that to the specific Freq of the MAF and create a dead on MAF table. Or am I missing something.
I’ve also come to the realization that the PCM is basing almost all of its LTFT adjustments based solely on our 02 sensors. So if our 02 sensors are in anyway slow, old, or week then we are tuning against bogus data right from the start. So could someone (someone better at math than me) create formula that put into an excel sheet would look at the 02 data and tell you that your 02’s were operating at sufficient amplitude and rate (assuming there wasn’t some other tuning issue causing unusual but valid 02 readings).
Information is power – we need to find the man or men that wrote the PCM source code and then we would no exactly what the PCM is doing and what sensors it’s using to calculate every thing out with.
which is derived from this equation:
VE = ((mass flow * IAT / (MAP * RPM * Displacement))
Were did you get your formula from?
If that is correct then I see a problem right of the bat. The IAT sensor is basically embedded in the plastic lid that as you know gets very hot and I'm 100% for sure that most of the time its reading is no were near actual intake air temp.
Next issue I have with that is doesn't installing a big cam change the MAP range of our motors? Shouldn't it lower the active range of the sensor? Wouldn't that invalidate the results of the equation?
You know if that equation is valid why couldn't we easily create an excel sheet that would take the Data Logs and do the calculations and then associate that to the specific Freq of the MAF and create a dead on MAF table. Or am I missing something.
I’ve also come to the realization that the PCM is basing almost all of its LTFT adjustments based solely on our 02 sensors. So if our 02 sensors are in anyway slow, old, or week then we are tuning against bogus data right from the start. So could someone (someone better at math than me) create formula that put into an excel sheet would look at the 02 data and tell you that your 02’s were operating at sufficient amplitude and rate (assuming there wasn’t some other tuning issue causing unusual but valid 02 readings).
Information is power – we need to find the man or men that wrote the PCM source code and then we would no exactly what the PCM is doing and what sensors it’s using to calculate every thing out with.
04-11-2005, 08:07 PM
#44
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Originally Posted by P Mack
The oxygen sensor doesn't measure the oxygen/fuel ratio. It compares the percentage of oxygen in the ambient air to the percentage oxygen in the exhaust. That's why you can't cut your o2 wires and solder them, cause it has the reference air in it. So if there's 20% less oxygen in the air and 20% less oxygen in the exhaust too, the sensor should read the same if I understand correctly.
Yes the O2 sensor does have a pocket of air inside and its output is derived in part by that, but it has nothing to do with the wire connecting it to the PCM.
Lambda Sensor
The structure of the conventional lambda sensor is shown above. Its main body is a U-shaped tube of zirconia electrolyte. Zirconia is a well-known oxygen ion conductor at high temperatures. Pt electrodes were pasted on both sides of the zirconia tube. The inner electrode communicates with the atmospheric air and the outer side with the exhasut gas. It is actually a potentiometric solid electrolyte cell and can be depicted as follows:
O2 (exaust), Pt | Solid Electrolyte (Zirconia) | Pt, O2 (air)
The electromotive force of the the cell is given by:
EMF = (RT/4F)log{PO2 (exhaust)/PO2 (air)}
The partial pressure of oxygen in the air(PO2 (air)) is almost constant and EMF depends on the oxygen pressure of the exhast gas (PO2 (exhaust)). In the lean, PO2 (exhaust) is close to PO2 (air) and EMF becomes almost 0V. However in the rich, equilibrium PO2 (exhaust) is negligible and EMF becomes about 1V. At the stoichiometric point, EMF is about 0.5V. The equilibrium pressure of oxygen abrubtly changes near the stoichiometric point and so EMF shows step change at this point. It is possible to detect whether fuel is lean or rich by measuring EMF of the lambda sensor.
References
1. Heinrich Dueker, Karl-Hermann Friese and Wof-Dieter Haecker, SAE Paper No. 750223, 1975
2. Eckehardt Hamann, Hansjorg Manger and Leo Steinke, SAE Paper No. 770401, 1977
3. Hans-Martin Wiedenmann, Lothar Raff and Rainer Noack, SAE Paper No. 840141
All credit good or bad goes to this web page and it has some good info on O2 sensors (even though technically this is an import site) -
http://home.flash.net/~lorint/lorin/fuel/lambda.htm
I think the cutting the wire theory is good, but for the reason that when your trying to get tuning nailed down to a range of 0.40 and 0.65 volts while cruising any extra resistance (like someone doing a crappy connection) would cause that range to change and fluctuate and the longer the wire the longer it would take for the PCM to receive changes (I'm sure its not much longer but still).
04-11-2005, 08:30 PM
#45
Well maybe the thing about not cutting your o2's is just an urban legend, i've never tried it myself. You have a point about the IAT. The pcm does make a correction for IAT based on ECT and you can adjust how much it's adjustded in hp tuners. Like if you do the tb bypass, you might want to change it. Somebody on this board moved their IAT sensor to the bellows and i think they had good results with it there.
04-11-2005, 08:38 PM
#46
Originally Posted by God Forgives I Dont
You know if that equation is valid why couldn't we easily create an excel sheet that would take the Data Logs and do the calculations and then associate that to the specific Freq of the MAF and create a dead on MAF table. Or am I missing something.
04-11-2005, 10:13 PM
#47
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Originally Posted by P Mack
Lol, this has been discussed many times before, both to calculate a ve table using the maf, and using the sd calcs to create a maf table. For one thing, you don't need to use the equation to do that because dynamic airflow does the calculation for you. For another thing, your results probably won't be very good as another_user has found out.
Exactly my point! That equation cannot be valid because it doesn't work!
Or it is valid but so many of the variables are too far off for it to work. We already no for fact that the IAT is wrong and I think our MAP range has changed do to the large cams and we changed our VE table.
Calculating with any of the methods we already discussed just doesn't seem to work very well in real life. So if the math is correct in the actual equations then that leaves only one answer, the input variables are not correct be it either the sensor itself or because of outside influences on the sensor such as the IAT sensor!
04-11-2005, 11:09 PM
#48
The equation is valid by definition. If you had perfect inputs you would get a perfect output. The problem when you have bias or precision error from a single sensor, and the output is multiplied by the output from other sensors, the error is also multiplied. Plus some sensors are too far upstream so there's a delay effect, a single sensor doesn't always give an average value for the whole airstream, and theres fudge factors (filter coefficients) that change the results too.
I still don't know what you're talking about with the map range changing due to large cams. I realize vacuum drops with a bigger cam, but so what? The map is accurate enough from 0 to 105 kpa, so what's the problem?
I still don't know what you're talking about with the map range changing due to large cams. I realize vacuum drops with a bigger cam, but so what? The map is accurate enough from 0 to 105 kpa, so what's the problem?
04-11-2005, 11:28 PM
#49
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Originally Posted by God Forgives I Dont
Mass flow = (VE * MAP * RPM * Displacement) / IAT
which is derived from this equation:
VE = ((mass flow * IAT / (MAP * RPM * Displacement))
Were did you get your formula from?
If that is correct then I see a problem right of the bat. The IAT sensor is basically embedded in the plastic lid that as you know gets very hot and I'm 100% for sure that most of the time its reading is no were near actual intake air temp.
Next issue I have with that is doesn't installing a big cam change the MAP range of our motors? Shouldn't it lower the active range of the sensor? Wouldn't that invalidate the results of the equation?
which is derived from this equation:
VE = ((mass flow * IAT / (MAP * RPM * Displacement))
Were did you get your formula from?
If that is correct then I see a problem right of the bat. The IAT sensor is basically embedded in the plastic lid that as you know gets very hot and I'm 100% for sure that most of the time its reading is no were near actual intake air temp.
Next issue I have with that is doesn't installing a big cam change the MAP range of our motors? Shouldn't it lower the active range of the sensor? Wouldn't that invalidate the results of the equation?
As far as the accuracy of the IAT sensor: I have referenced it against the actual outside temp, and generally find it to be within a few degrees. Keep in mind that the sensor filament is suspended away from the body of the lid and in the path of the intake air. Also, I don't know about you, but if I immediately open the hood and touch the air lid after driving around for awhile, it's always cool to the touch. I think that in most cirumstances, the IAT reading is within a reasonable percentage of error. Realize also, that the PCM has the ability to compensate for inaccuracies in IAT and MAP sensor data by using fuel trims.
As for MAP: it's a pressure reading that is directly proportional to the amount of air entering the engine. Simple as that. Sure, an aftermarket cam is going to change your MAP values for different operating ranges, but like P Mack says, "So what?". The MAP sensor is still going to read the air pressure in the intake manifold regardless.
One main thing to remember: Yes, the mass flow calculation will not result in perfect fueling all the time. That is why we have fuel trims. Of course, the O2's are not always accurate either, but with this system of checks and balances we get an end result that is pretty accurate in most situations.
04-12-2005, 10:27 AM
#50
Originally Posted by P Mack
That's why you can't cut your o2 wires and solder them, cause it has the reference air in it.
yea, urban legend man.
the reason most people have problems with cutting their O2s is that they suck at it. not a nice thing to say, but its true.
see, the 02 voltage is in milivolts.... as in, less then one volt. so any SMALL resistance change, will have a large effect on its readings.
the weatherpack connectors used, have a really good, low resistance connection. so they dont cause a drop... same with the extention wires.
you can NOT use any type of crimp connector, and expect there to be a good electrical connection.... however, if you use good wire, and if you properly solder and heatshink a extention, it works perfectly fine.
the problem happens from crimp connectors, bad solder joints ect.... not from the fact they're extended.
04-12-2005, 10:45 AM
#51
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Originally Posted by God Forgives I Dont
Exactly my point! That equation cannot be valid because it doesn't work!
Or it is valid but so many of the variables are too far off for it to work. We already no for fact that the IAT is wrong and I think our MAP range has changed do to the large cams and we changed our VE table.
Calculating with any of the methods we already discussed just doesn't seem to work very well in real life. So if the math is correct in the actual equations then that leaves only one answer, the input variables are not correct be it either the sensor itself or because of outside influences on the sensor such as the IAT sensor!
Or it is valid but so many of the variables are too far off for it to work. We already no for fact that the IAT is wrong and I think our MAP range has changed do to the large cams and we changed our VE table.
Calculating with any of the methods we already discussed just doesn't seem to work very well in real life. So if the math is correct in the actual equations then that leaves only one answer, the input variables are not correct be it either the sensor itself or because of outside influences on the sensor such as the IAT sensor!
07-03-2005, 12:12 PM
#55
A mention of the waterproof feature that's present on numerous recent versions is appropriate here. All it means is that the reference air isn't picked up through a vent right at the sensor itself where water and other contaminants are plentiful. Instead, there's a sealed sleeve of insulation that runs up into the harness, or even all the way to the PCM, before it opens to the atmosphere. Since only a tiny amount of reference air is needed, enough will flow between the gaps in the stranded wires inside the insulation. You can get into trouble if you solder these cables because it wouldn't take much flux, solder, or melted plastic to block those essential gaps.
Amazing what you can find with one minute on google.
