[JohnSub2013sti]

I didn't want to post this but.... should a cold air intake be resulting in both positive and negative AFR's ?
This is logging from a stock map

It's concerning me tbh and it's not what i expected ...

 

[yamahaSHO]

You will get wild swings from AF Correction. What you're more concerned with is the AF Learning. Under steady load/throttle, you can use both to find final correction.

 

[JohnSub2013sti]

Thank you for the reply. So you would expect this behavior from an unscaled Maf when looking at total correction ?

Do you have a good reference to read regarding finding the correct final correction?

My expectation for the change in flow rate with a cold air intake was that it would read lean across the board
Since Mafs measure the rate of cooling to operate...

These would be my initial corrections. I just didn't think they would be this large..... It almost makes me want to check for vacuum leaks

 

[JohnSub2013sti]

Does anyone have input on this? I'm worried this is mechanical as opposed to a tunning problem
Maybe someone could post the change in there maf scaling with a cold air intake (I know it won't be exactly the same)

Also feel free to call me out if I'm being stupid about something

Edit here's a random stage 2 map comparison i found online

 

[yamahaSHO]

Scaling a MAF is pretty simple. Start with your OEM intake diameter, then calculate the new area of the new ID.

A = π r²

From there, you can use the fuel trims to scale the MAF, referencing voltage. You don't have to hit every value... You can skip around and interpolate based of overall trim (don't interpolate more than one value at a time). Once you have it scaled, you can move on to Load Compensation.

For MAF scaling, I don't even use spreadsheets, histograms, plotting, etc. It's a 2D table, so no need to complicate it.

 

[JohnSub2013sti]

Thank you this makes complete sense.... and is what I would expect.

But if this is how it works then why am I getting both negative and positive afr learning

The method you described would mean a cold air intake leans the engine out for the complete table

Unless I'm mistaken

Sent from my SM-S901W using Tapatalk

 

[yamahaSHO]

The 'cold air' part doesn't particularly matter. That said, MAF's inherently measure air differently at hot vs cold temperatures, which is why there is a table in place for that... That Subaru populates with zeros... I don't leave this with zeros.

An intake change can introduce turbulence or change the flow character around/through the MAF sensor location, which can have an effect, like a larger MAF needing less of a correction in low flow, vs high.

 

[JohnSub2013sti]

This is what I've changed for now

at least my AFR wont be off under 50g/s

 

[yamahaSHO]

Now interpolate it so it's as smooth as the original.

 

[JohnSub2013sti]

Ya i'll do that... This might be a stupid question but

How would I scale the maf beyond 60 g/s (transition from closed loop to open loop fueling).
Do i just use the interpolation curve ?

 

[yamahaSHO]

You use a WBO2 to log your AFR and adjust based off target vs actual.

 

[JohnSub2013sti]

Do you have a recommendation on a wide band with maximum accuracy ?

I found a Prosport kit that would be nice. I also see a lot of people using AEM. I assume you would reccomend COBB though ?

 

[yamahaSHO]

ProSport is probably on the low end. I am a big fan of PLX Devices, which is what I have been using for years. I may have a DM-6 for sale soon. I have an AEM dash now and don't need an external display.

 

[JohnSub2013sti]

Thanks man you've been a big help.

I was going to do some calculations on open loop MAF scaling (with my stock sensor). I have a 32-bit ECU where the O2 sensor works over a wider range but is skewed due to it being in the front exhaust pipe (exaughst back pressure). I wanted to do this just to learn a bit and see how off the values would be

I was using this guide as a reference
HOWTO: One Man's Way of Scaling a MAF - NASIOC

....
but then I realized I don't even understand how the AFR Correction 1 is calculated in closed loop
I figured it would be

A/F Sensor #1 / (1 - A/F Correction #1 * 100) = Closed Loop Fueling Target

But that doesn't seem to work.... do you know how its calculated

Sorry for all the questions lol

 

[yamahaSHO]

Don't use the stock sensor in open loop. It's inaccurate there... By a lot. That's why the car still uses open loop and not full-time closed loop, like nearly every other new car out there.

AF Correction + AF Learning give you final correction (AFL of 10% and AFC of -5 is a final value of +5% fuel correction, at that time). In the case of MAF scaling, you can add the two for usable data ONLY when it's done over a constant load. Any load/throttle changes will introduce transient fueling changes and AF Correction will swing back and forth and have little value in what you're trying to do. For quick data, given the car has had time to accumulate AF Learning data, use that a few times and you'll get it close.

Closed loop fueling target has nothing to do with the corrections. The corrections are trying to reach the fueling target set by the base fueling and fueling compensations.

 

[JohnSub2013sti]

Thanks again! I have one final question

A/F Correction #1 (%) & AF Learning 1 are closed loop short term and long-term fueling corrections in closed loop, right?
Subaru Monitor List - Customer Support Center - Confluence (atlassian.net)
But what would the right parameters be in open loop?

 

[yamahaSHO]

AF Correction 1 and AF Learning 1 are the currently applied values (think, real-time). Realistically, that's all you need and non of the others for CL.

Open loop literally means that the feedback loop is not closed... This means that you have no feedback to tell the ECU if fueling is off or not. There are NO parameters to log and generally, NO fuel trims are applied (there's a small caveat, but most of us remove that for the short amount of low boost you might see AF Learning applied) and you need a wideband O2 to log actual AFR vs Commanded Fuel Final, referencing it to MAFv. You will NEVER get OL sorted properly without a WBO2, especially if you don't have the experience on any given platform/setup. I will tune most "staged" cars without a WBO2, but anything more, I cannot dial in fuel correctly in higher loads which all fall under OL.

Many of the newer cars, to include SxS' (as well as probably every aftermarket ECU), use closed loop fueling all the time... And they provide correction much more quickly and accurately.

 

[JohnSub2013sti]

Thats what i thought.... But this utility here (designed for maf scaling)
RomRaider • View topic - UTILITY: CL/WOT MAF Scaling | Log View/Stats | Load/IAT Comp

Accept fuel trims in both Open Loop and Closed Loop....
And it was made for Subarus... which has me confused

Open Loop

Close Loop

Edit: I also ordered a AEM wideband

 

[yamahaSHO]

Honestly, you can do MAF scaling faster by hand. I don't use any tools when I scale a MAF. I think people complicate this... It has to have a proper and smooth curve, and then get it all close.

Tools and spreadsheets generally give you an output that isn't representative to the above. Running a log like the screenshot (closed loop), can give you a pretty good idea on the trends in certain areas of the MAF curve which you can then interpolate. If your MAF curve was close in that you did the math for the area difference, you can knock this out in like 2-3 revisions.

 

[JoeC]

Man this thread is way above my automotive knowledge but it sure is fun to read.