90c350

Hey just a quick dumb question?? I'm wondering if you change the Stoich afr from say 14.7 to something like 14.2 will this help it run a little richer in closed loop?? Just asking so that I can play around, untill the wideband show's up> Thanks again

91chevz71

In theory I guess it could work

Your VE table is tuned for 14.7 now, so the computer might be playing catchup a lot. Just retune it for 14.3 and it *should* work out ok.
Again, assuming everything else is right like BPC, etc. GOnna have to do some trial & error, which is half the fun anyway

91L98Z28

My understanding is that the answer is NO.

As long as you are in closed loop, you're going to oscillate around stoich. That's what closed loop means - no matter what the code spits out for an injector pulse width, the o2 sensor is going to feed back into the loop and cause a change in the injector pulse width (via BLM/INT) in order to establish oscillation around stoich.

91chevz71

Oscillate by how much, normally? Why wouldn't you be able to change the target stoich AFR? Would you have to adjust the O2 voltages to accompany the target AFR change?

91L98Z28

all this and far more is in the archives if you search, but i'll hash out the basics:

The purpose of a closed loop system is to use a feedback sensor (in this case, the O2 sensor) to correct whatever calculations/assumptions were made. In a general sense, as long as the O2 sensor is indicating oxygen in the exhaust, the ecm will richen up the mixture, and as long as the O2 sensor is indicating no oxygen in the exhaust, the ecm will lean the mixture. That is the essential component of closed loop: not to achieve a stoichiometric AFR, but to oscilliate about it. This oscilliation is necessary for a catalitic converter to do it's job, sticking near stoich is necessary for emissions.

stoich is slang/short for "stoichiometric" which is a chemistry term. in a combustion process involving oxygen, every "fuel" has a stoichiometric ratio that the fuel burns in. Regular automotive gasoline is taken to be approximately 14.7:1. In other words, you need 14.7 parts of oxygen to burn 1 part fuel.

The computer calculates how much air you've put into the system. In the case of MAF, it measures this directly (the MAF sensor reads in grams/sec); and in the case of MAP it calculates the value. Alcohol on the other hand is around 6.5:1, that's why alcohol cars need lots bigger carb jets, fuel pumps, etc.; they flow about twice the amount of fuel as a regular car for a given HP/airflow.

Once you know how much air you've put into the system, the stoich ratio can be used to determine how much fuel you need. If you're feeding 14.7grams/second of oxygen, then you need 1 gram of fuel, assuming a 14.7:1 stoich ratio (and ignoring the affects of the actual oxygen/nitrogen content of air, which is beyond the scope of this post).

Anyways, getting back on topic:

changing the stoich value is NOT going to change your achieved AFR. Lets say you cut it down to 14.0:1 in the code. Great, the computer thinks it needs MORE fuel per unit air, so it richens the mixture. Now, the o2 sensor suddenly sees that there is no oxygen in the exhaust, and immediately re-leans the mixture (via feedback, the essence of closed loop) and puts you right back at oscillating around 14.7:1, which it achives by lowering the BLM.

If you want to run an AFR of ANYTHING other than an approximate 14.7:1, then you must go open loop. the purpose of closed loop is to achieve and maintain stoich for whatever fuel you happen to be using via change to blm/int.

This is how older cars like ours, in stock form, can use todays's modern mtbe/ethanol fuel mixes, which often have stoich fuel values different from 14.7:1. MTBE fuels can be as low as 14.0:1 or so.

as for how much the car osccilates around stoich, well, it varies. a fully warmed up engine with a good heated O2 sensor that is fresh and new, everything running properly, will oscillate very little and stay rather tightly around 14.7:1.

An old, high miles, non-heated o2 sensor in a semi-cool header tube will not be able to sense/track the oxygen content of the exhaust nearly as well, and as such the swings (called crosscounts) will be much slower in coming and the AFR will vary more widely.

If the O2 sensor isn't hot enough, it won't work at all; and if it's old and clogged/coated/whatever, then it is not nearly as fast as a new one.

thats why guys with long tube headers almost always have to run heated O2's, there isn't enough heat in the header tube by that point (much has been radiated upstream) to keep the O2 sensor reading properly.

Others with more detailed knowlege, please correct/add where necessary!

91chevz71

appreciate it L98

getsideways

l98, youre not quite right about not bieng able to target anything other than 14.7 in closed loop.

91chevz71, there is a good explanition from rbob in the tuning stickies named "fueling logic (o2 swing points)". this should clear up your question.

i curently target 14.13 in closed loop for my 10% ethanol here in az.

91L98Z28

the post I made was targeted primarly at a fuel with an assumed AFR of 14.7:1. The "more correct" statement which applies to alternative fuels with stoich values other than ~ 14.7:1 is:

You can not target anything other than stoich in closed loop; by definition the target of this type of closed loop system is a stoich AFR.

For example, let's assume your 10% ethanol fuel in AZ is really a 14.1:1 stoich fuel. let's also assume that your'e in closed loop operation.
In this example, because you're closed loop, your AFR will be oscillating about the stoich ratio for this fuel: 14.1:1. Let's assume you have a perfect BLM/INT of 128/128 in this condition.

Now, let's assume you drive somewhere else, and put in a "normal" 14.7:1 fuel into the tank, with NO other changes. Again assuming closed loop operation.
In THIS case, because you're closed loop, your AFR will still be oscillating about the stoich ratio for this fuel, but in THIS case, that ratio is 14.7:1. You will notice that in this case, your BLM will be about 4% lower than before, it will go to 123 or so.

If you decided you wanted to run this new fuel permanently, you would change your stoich AFR in the BIN to 14.7:1, and your BLM would return to 128.

Closed loop "targets" stoich. The stoic AFR you put into the .BIN is just part of the math to determine the pulsewidth to run to the injectors, it is NOT a target for an actual AFR. You could put a value of 14.0:1 in the stoich AFR value in the BIN, and test two gases in closed loop (a 13.0:1 gas and a 15.0:1 gas), and your AFR is going to be oscillating about 13.0:1 or 15.0:1 (respectively), NOT 14.0:1.

With a standard narrow band O2 sensor, you can NOT target and actively maintain a closed loop AFR significantly different than stoich, because the O2 sensor goes dead, and you no longer have feedback, and then by definition you no longer have a closed loop system.

getsideways

good stuff. im still learning this and for some reason this topic about targeting different stoich afr's and o2 swing points in c/l is just not sinking in.

91L98Z28

don't think of it as targeting different stoich AFR"s.

instead, think of it as simply targeting stoich. The stoich AFR value in the .BIN is just an input into a math equation on how to get close to stoich for the intended fuel, NOT a decree to run some actual AFR.

let's simplify down o2 sensor operation and get a bit theoretical:

The O2 sensor does one thing really well: it tells you whether or not there is oxygen in the exhaust.

A high voltage output means "no oxygen", and a low voltage output means "oxygen".

Or, in another way of looking at it, a high voltage means "richer than stoich" and a low value means "leaner than stoich".

in closed loop, the injector pulsewidth is NEVER held steady. it's constantly increasing, or constantly decreasing. If the o2 sensor output is high ("richer than stoich"), then the ecm will decrease injector pulsewidth to go leaner, and if o2 sensor output is low ("leaner than stoich"), then it will increase pulsewidth to go richer.

theoretical example illustrating 5 crosscounts:

time(s) pulsewidth o2 out
000.1 250.00ms high
000.2 249.00ms high
000.3 248.00ms high
000.4 247.00ms low
000.5 248.00ms low
000.6 249.00ms high
000.7 248.00ms low
000.9 249.00ms high
001.0 248.00ms high
001.1 247.00ms high
001.2 246.00ms low

In the above example, AFR doesn't matter. All the feedback loop needs to know is that if the o2 output is high, then you are richer than stoich, and should pull a tiny bit of fuel out; and vice versa. Every time you switch from "leaner than stoich" to "richer than stoich", you have a crosscount.

The ECM KNOWS how much air is going through the engine (either directly measured with MAF, or calculated with SD); the purpose of the stoich AFR value in the .BIN is simply to enable the math calculation to figure out initial injector pulsewidth.

If the stoich aFR value in the BIN is wrong (such as running 14.0:1 fuel with a stoich AFR value in the .BIN of 14.7:1); then the resultant injector pulsewidth will not lead to a stoich fuel ratio. In this case (14.7:1 in the BIN, 14.0:1 actual fuel) the initial, uncorrected pulsewidth will result in a lean mixture.

Something like this would happen:

time(s) pulsewidth o2 out
000.1 250.00ms low
000.2 252.00ms low
000.3 254.00ms low
000.4 256.00ms low
000.5 258.00ms low
000.6 260.00ms low
000.7 262.00ms low
000.9 264.00ms low
001.0 266.00ms high
001.1 264.00ms low
001.2 266.00ms low
001.3 268.00ms high
001.4 266.00ms low
001.5 268.00ms high

The initial calculated pulsewidth lead to a lean mixture, and the o2 was stuck low. so, the pulsewidth was continually increased (by raising the BLM), until the o2 output started to generate crosscounts again, at which point the stoich AFR was achieved again.

closed loop will always seek and achieve the ACTUAL stoich value for the fuel you're burning (ignoring big cams and other beyond-scope-of-post issues).

Fullsizewagon

I'm a far cry from being able to do this myself, but I would have thought it was "simply" a matter of finding where/what code is targeted at 500mV (or possibly 50% duty?) from the O2 sensor. After all the sensor characteristic is not completely square, it has a slope so that a 150 to 850mV signal could be targeted, giving a tuning range of perhaps 12.5 to 16 (or whatever the slope allows for). Doing this with some hardware shifting the voltage from the O2 sensor would be easy, so I'm convinced that the software also could be modified to do it.

RBob

iTrader: (1)

No need to modify the code. There are look up tables for the targeted O2 values.

RBob.

Cflick

If you plot one, you'll more likely find that the range of full on to full off of a standard narrow band sensor is closer to 14.5 to 14.9
There are tables to target a different ratio, but myself, I'm still in the "make it run right stock" mode.

91L98Z28

This topic is one of my pet peeves, and I have strong opinions on it. You've been warned. =)

I know that it is very popular and "desirable" to assign various AFR values to a narrow band O2 sensor's output voltage, but you just cannot do that. it is not a linear device, not even _close_ to being linear, and it's not even _close_ to having a slope. It was never designed for, and is not able to, tell you what your AFR is. That's why they invented WB O2 sensors.

The purpose of the narrow band O2 sensor is two-fold:

1) when a fuel mixture (AFR) is constantly altered in order to drive the O2 sensor voltage up and down, you will constantly be going richer and leaner than stoich, which keeps a catalytic converter happy and functioning (emissions). I think it was Grumpy who made some good posts on this topic in the past...about how a cat. converter NEEDS a mixture that rapidly goes slightly rich/slightly lean to work effectively.

2) when you rapidly adjust a fuel mixture so that it goes back and forth slightly from rich and lean repeatedly, the AVERAGE is roughly the stoich mixture for the fuel being consumed, which minimizes the nasties produced from the combusion process. (emissions). When everything is working well (a well heated, fast O2 sensor, engine in proper repair, etc.) the rich/lean swings are not all that large and you end up with a pretty good average stoich AFR.

Thus the two primary purposes for a NBO2 sensor are emissions purposes. They started using them in the late 70s / early 80s to make the catalytic converters more effective, and to reduce emissions to comply with ever stricter emissions laws, oh and it helped with fuel mileage too. Nowhere in the design of a NBO2 were they ever built to measure AFR.

Take a look at my post in this thread, and especially take a look at the image attachment:

https://www.thirdgen.org/forums/diy-...nificance.html

The image I attached in that thread is a comparison chart of the readings of a narrow band O2 sensor vs. a wide band O2 sensor, mounted in the same exhaust mainfold, approximately two inches away from each other. In other words, the sensors were measuring and recording the SAME exhaust gas.

Fullsizewagon

Ok, so much for my "knowledge" about that issue.. Seeing the data collected by 91L98Z28 explains it all! Great work! There's no slope to speak of at all to the nbO2 sensors, + the spread (or whatever it's called) makes it hopeless to use them for anything but on/off indication, that's easy to see.. The charts I have seen elsewhere gave the impression of a certain slope.. So simply put, the limitation is not in the software, but the nbO2's are just too narrow and have too much "spread" to be used for anything but 14.7:1.. Too bad..

91L98Z28

For me anyways, it's amazing how much I thought I knew, then how much I learned, .... and then how much I had to re-learn because what I initially thought I knew to be true, was in fact wrong. And then of course there is still how much I have yet to learn.

The NBO2 correlating to any given AFR is really a pet peeve of mine because of this. It's such a basic fallacy and (in my opinion) contributes to confusion and lack of understanding about how to tune EFI because it leads you in so many directions that just don't work or are wrong.

I think part of the reason it persists is because it's just so darn convenient. All our cars already come with NBO2's, and the mV reading is easy to datalog... It's really convenient to grab some mV to AFR chart and believe it.

"Friends don't let Friends tune AFR with NBO2's"

91chevz71

Well, I spliced my wideband's narrow-band simulated lead into the harness, now the ZT-2 is feeding both AFR data and INT/BLM data to the EBL. This has seemingly cured my closed loop issues. AFR changes fast from 14.3-15.1/2 while driving around...proportional gains? Closed loop seems to work correctly. Nice to have it back!!

Cflick

Depends how sophisticated the friend !
If that friend understands that greater than 500 milivolts means an AFR somewhere between 5.0/1 ( where gasoline becomes a fire extinguisher ) and 14.7, and less than 400 milivolts means an AFR between 14.6 and about 20/1 ( where there's no gas to speak of )
( yes, my overlap is deliberate ) and that milivolts between 400 and 500 mean essentially nothing other than an AFR somewhere between 8 and 20, but that a swing means that the AFR is crossing 14.65 at some point during that swing, then that friend can probably tune just fine with a narrow band, within limitations of narrow band tuning.
The ONLY way I know to get an accurate AFR from a narrow band, is to get it to swing symetrically, ( that's an equal time high and low ) and record the grams/minute fuel, and CFM air at the moment of the swing, ( or averaged over several identical symetrical swings ) assume that's 14.65 AFR, and start calculating deviations.
It helps ( a lot ) if you're better than I am with calculus.
Of course, the manufacturing tolerances of the narrowband means that the swing point could be most anywhere between 14.4 and 15, so there are limitations on this method.
Also, stoich means exactly ZERO oxygen in the exhaust. No more, and no less.
Since this is not possible with a real engine, assumptions are made as to how much oxygen there will be in the exhaust of a perfectly running engine, which will vary with design of that engine, so trying to get an exact AFR with a narrow band at any given moment is pointless.
The variances in sensors and engines makes this a falacy, but the cross point can be infered and assume to be 14.65 AFR with reasonable accuracy.
Remember too, that the narrowband uses the output of the zirconium directly, while the wide band uses the corrections to the pump current. Although they ultimately measure the same thing, the methodology is completely different.

Now, I hope that this all serves to enlighten, and not to confuse.....

Ronny

iTrader: (1)

Question for 91L... Maybe it was said but my understanding is that the WB02 does not measure A/F ratio but the amount of 02 in the mix it sees in ext stream. Please correct if that is not 99% correct.

so that being said. after datalogging for a while my car with WB02 functional, i would notice at cruise speeds(no DFCO or HWY cruise in .bin) of 65 at 1800 rpms that I would see the CL at around 14.7 to 15.1 meandering about. this is with stoich commanded to 14.3 (10% ethanol) in EBL.bin. I will assume either the WB is off(calibrated to fresh air and new) or the tune is not right or the NB02 is not right(Delcoheated). I was taught the WB is very accurate so will believe it. I am OK with that discrepancy.

Now what alarmed me is my OL idle was 15.0 to 15.5 on WB from day to day commanded to I will say is 14.0/1. It was suggested it may be my cam 224/230 @ .05 114 LSA? overlap. So paragraph #1 my WB reads 02 only and is reading the infusion of fresh air from the overlap and i should leave A/F OL idle commanded to 14/1 and not be concerned?

91L98Z28

Well, I'll respond, since it was directed at me, but others should respond too.

First, correct, none of these sensors can actually measure the ACTUAL AFR. You need a multiple-gas exhaust analyzer to do that, and knowledge of the fuel you're burning, and probably more than that that I'm not aware of. And even then there's going to be wiggle room, in my opinion.

The WB sensor is capable of producing a usable AFR resultant value, provided that you know something about the fuel you're burning. The WB doesn't measure the AFR, it measures the after-effects of combustion and tells you how close to stoich the after-effects seem to be.

Digging deeper: What the WB sensor is actually measuring is something called Lambda. Lambda is a percentage difference between the stoich AFR and the actual AFR for any given fuel. Because the value is only a percentage, the lambda value itself is unitless and expressed merely as a number.

Lambda is defined as (actual AFR) / (stoich AFR)

Let's say you had three different fuels, all being burned ~ 10% richer than stoich (or lambda 0.9).

Lambda 0.9 for the 14.7:1 fuel is about 13.2:1.
Lambda 0.9 for a 14.3:1 fuel is about 12.9:1.
Lambda 0.9 for the 6.5:1 fuel is about 5.9:1.

The lambda (the ratio between stoich and acutal AFR) numerical _value_ is the same, but it translates to a very different "AFR" depending upon the fuel you're using.

If you know you are using a 14.3:1 fuel, and want your WBo2 to give you a more accurate AFR, then you need to configure your WBO2 to output values in lambda, and then scale to your 14.3:1 fuel. Lambda 1.0 on a 14.7:1 fuel is 14.7:1, Lambda 1.0 on 14.3:1 fuel is 14.3:1. The WBO2 measures the same lambda, but the actual resultant calculated AFR is different.

NBo2's lack the necessary hardware to measure lambda, but they WILL tell you if lambda is less than 1.0, or greater than 1.0, by observing their output voltage and trend (output starts low, trends high, then lambda is < 1.0). But the same logic applies as above - if you're running a 14.3:1 fuel, your NBO2 sensor is going to oscilliate about a 14.3:1 achieved AFR so long as you are in closed loop and everything is working correctly.

The above discussion IGNORES the effects of big cams.

I know that choppier cams can put raw oxygen into the exhaust and skew the results/measurement. I have no experience in this area, as I have not converted my '71 to EFI yet, but with it's 240/248 (@ 0.050) cam, I know that I'll be learning a lot.

Ronny

iTrader: (1)

Thank you. that was helpfull.

I just discovered I never calibrated my WB02 logs for the fuel I am using. It appears that will be necessary if I expect to see the WB A/F to be what I am asking NB to create CL(14.3). But the Innovate unit has no provision that I am aware of to affect the display on output to a gauge. I can adjust the logs however. The lambda however should always read 1.00(CL) if all fuel and air is combusted, as we would like, as WB only reads unburned 02 and responds with a fiqure above or below 1.00. So I should ignore the digital WB gauge as far as A/F ratio goes since I cannot adjust and only look at lambda(1.00=14.3) as far as analog gauge goes ?

As I stated the stoich A/F in .bin is 14.3/1 commanded. My the swing points of 02 sensor were moved up in voltage a tad(10%?) and a bit tighter to the median voltage.

Cflick

Too often too many want to use a WbO2 as an AFR meter, which it is not.
Kind of like a voltmeter calibrated in watts, it will be accurate only if other conditions are met.
The wide band measures oxygen content in the exhaust, not AFR. That's why a rich misfire can register as lean. ( or a large cam overlap especially at low speed )
IF the wideband is calibrated to show roughly 0.5% O2 as 14.7 AFR, then whenever the exhaust O2 content hits 0.5% that unit will display 14.7/1, even if used on nitro methane where that O2 content actually represents something much closer to 1.7/1, OR on an excessively rich engine with an exhaust leak sucking wind upstream of the sensor.
This does not negate the value of the instrument !
Better, would be to calibrate it in terms of % O2, and look up the AFR for that percentage O2 with that fuel, but then I'd have to think.
Gawd, we can't have that ! :-)
Equally valid, would be to calibrate it in terms of % Stoich, or Lambda.
It can easily show 5% rich ( or 15% lean, or whatever ) regardless of fuel, but AFR for only one fuel.
Also note that although wide band in nature, the O2 curve is furthest from linear AT stoich.
It becomes very linear lean of 15/1 ( gasoline ) and becomes essentially flat richer than about 13/1.
It's a very useful ( and cheap ) tool for finding stoich, and for lean mix.
The same is essentially true of CO, but in reverse. It's very linear richer than about 14.2/1 but essentially flat leaner than about 16/1.
Combine a wide band O2 with a wide band CO, and you've really got something !

Yes, you *could* calibrate your gas guage in miles-to-go directly, but for most E,1/4,1/2,3/4,F is good enough for all intents and purposes. You can't calculate milage with it, but you could, roughly, if you re-calibrated it in gallons.
Of course, it would be little help if your country uses kilometers and not miles.
All this is true of the wide band. Use it, but be aware of what it's *really* telling you.

SO, that 14.7 doesn't mean 14.7 on alcohol, but it does mean stoich.
----------
I don't think that's "commanded" so much as providing the AFR reference number to use elsewhere, when it wants 5% more of this, or 7% less of that.
Something to use in the calculations, not something to "command" per se, but I could be wrong.