AFR Tuning Without Wideband

[Another_User]

I was bored again, so I wanted to see if air fuel ratio tuning was possible without a wideband O2 sensor. What I really need is someone with a wideband and some spare time to sanity check my calculations.

Basically my theory was that it would be possible to calculate your AFR based off airflow and calculated fuel flow. My first run was with MAF airflow and calculated fuel flow based on injector rating. Based on what I recorded, the computer calculation based on *uncorrected* MAF airflow is almost dead on with what the computer is commanding. This led me to step two, same process, but using MAF freq error airflow, which I would think is a calculation of what your airflow really is. Again, almost exactly where I expected it to be.

The uploaded XLS shows the run and my calculations if anybody has a wideband O2 and could verify this is close.

[S2H]

sorry to say...as weather changes so will all of those values...
its not possible to do any of that without a real wideband
AFR is not something you can calculate from airflow...
there are many factors at stake...and you havent even accounted for timing changes....

[Another_User]

sorry to say...as weather changes so will all of those values...
its not possible to do any of that without a real wideband
AFR is not something you can calculate from airflow...
there are many factors at stake...and you havent even accounted for timing changes....

Shouldn't it recalculate for weather? Timing won't actually affect the AFR because you are calculating based on fuel and air flow...just the effectiveness of the burn will change, which would affect O2 readings. I would think close would be good enough, since really tuning should be done on a dyno...(ha!) That's why I want to find a comparison. Or even somebody that will log all the data so I can make the calculations! If it was within a few tenths of what the wideband O2 is, it could be really useful as a poor mans air fuel meter. WAYYY more useful than air fuel meters that run off of narrow band, and they sell tons of those.

[S2H]

Timing can affect the fueling quite drastically
I've had ad little as 3* throw the afr off by half a point
Usually it takes more than that... But timing always affects afr.. Which is why when you tune you have to do both at the same time

[BSmith]

So if timing effects fueling, it would effect air flow, which goes back to the measurements being close?

[S2H]

spark doesnt effect airflow at all....

airflow stays the same.....gets measured by MAF/MAP
pcm looks up value in spark table..
fuel gets burnt....
end result AFR
doesnt matter if you have a little airflow or a lot...
you change the spark..you change the burn...you get a different AFR result

example
WOT....
exact same airflow all the time...lets say you are in the .72 cyl air cells
if you have 20* spark you get AFR 12.5
then you add 5* spark..suddenly you might have ARF 13.0
o2's measure remaining Oxygen...not fuel mixture in the cylinder before it gets burnt

[Another_User]

Wouldn't that make the wideband O2 incorrect, and not the calculation?

spark doesnt effect airflow at all....

airflow stays the same.....gets measured by MAF/MAP
pcm looks up value in spark table..
fuel gets burnt....
end result AFR
doesnt matter if you have a little airflow or a lot...
you change the spark..you change the burn...you get a different AFR result

example
WOT....
exact same airflow all the time...lets say you are in the .72 cyl air cells
if you have 20* spark you get AFR 12.5
then you add 5* spark..suddenly you might have ARF 13.0
o2's measure remaining Oxygen...not fuel mixture in the cylinder before it gets burnt

[S2H]

No... You obviously aren't comprehending what we do with the wideband

You are calculating fuel dumped in.. It's not the same as fuel burnt
Fuel burnt is what makes power..
Burn the fuel too soon at too late and you don't get a complete burn.. Which means your afr is going to change
Burn at exactly the right time and your calculation works...
But you have no way of correcting your formula for that spark that is probably never going to be at the exact right time

Remember
We don't care how much fuel you dump in..(which is what you are calculating right now)
All we care about is how much of that fuel burns in the combustion chamber... Measurable by our wideband o2

[S2H]

And your formula is flawwed by missing some key things

The fuel atomizes differently with different velocities...
So airmass alone isn't enough... Velocity of airmass is extremely important

Not only that but your airmass is calculated based on values the user can change in the tune... So change somehting to a new value and the whole calculation goes to crap

[WS6FirebirdTA00]

If you are tuning with a WB, it is to dial in your airflow tables. If your airflow tables are not dialed in, you can not simply calculate anything with any sort of accuracy.

[eficalibrator]

Basically my theory was that it would be possible to calculate your AFR based off airflow and calculated fuel flow.

Calculating "AFR" based on ECU reported airflow and ECU reported fuel flow will just result in a number that exactly follows the commanded AFR. The fuel mass calculated for delivery is a direct result of the measured airmass and the commanded ratio. That's how the ECU works.

We use the wideband to see where we're at in actual delivered ratio. If we used accurate fuel injector characteristics and took careful wideband measurements, we can use that to assume an error between the reported airflow and reality. This wideband error (taken from a good instrument, and with the ASSumption of accurate fuel delivery) is how we correct the reported airflow in the field.

If you try to do the "Calculated AFR" as you suggest, you'll always come up with 0% error from the commanded regardless of how far out to lunch you really are. Just use a good quality wideband.

[mowton]

So if timing effects fueling, it would effect air flow, which goes back to the measurements being close?

My $.02.....

Timing doesn't effect fueling, it effects the result of the burn. Remember the WB (or NB for that matter) is determining the amount of O2 left over and providing you the "effectiveness of the combustion. Timing has a great deal to do with the efficiency of the burn

Thanks for listening.........am I correct

[LSX378]

My $.02.....

Timing doesn't effect fueling, it effects the result of the burn. Remember the WB (or NB for that matter) is determining the amount of O2 left over and providing you the "effectiveness of the combustion. Timing has a great deal to do with the efficiency of the burn

Thanks for listening.........am I correct

I'd say you are pretty close to if not on the mark .

Timing does affect the measured AFR.

In simple terms, advanced timing starts the burn early and will have a more completely burned mixture with lower HC, higher Nox and less free oxygen. The measured AFR will tend towards a larger number.

Retarded timing generally sees the burn start later, with higher HC, lower Nox and more free oxygen as the mixture tends to be less completely burned. The measured AFR will tend towards a lower number.

In simple/general terms! A more complex example mentioned by SoundEngineer is the turbulence of the mixture and its completeness of burn. A stationary mixture will generally indicate richer than a highly turbulent mixture. Higher compression will give a more complete burn than lower compression. The commanded AFR's can be identical. The measured will not.

They may not be far off on simple commanded terms, but they MAY be far off. Which is what the WB helps guard against.

There are timing modifiers based on commanded AFR's, but again these are predictive and based on the behavior of a stock tune, not adaptive which is what the wide band allows on a non stock tune. (manual adaptation ).

The airflow based predictions of what AFR should be, are very close for Open Loop stock tunes. They need to be to demonstrate EPA compliance. Away from stock, wide band is a good idea! (ref the other posts i.e. Greg, EFICalibrator. He spends his life on this stuff!)

Cheers!