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Old 03-04-2004, 11:07 PM   #1
Bolster
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Default Open loop fueling?

I wish I could say I totally understand everything, but that just wouldn't be true. I've got a few questions and these stem from the new UTEC 4.1 release.

1) Can someone fill me in on open loop fueling vs closed loop?

2) Will it provide '02-'03 WRX's any advantages/disadvantages?
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Old 03-04-2004, 11:25 PM   #2
Mildmanneredman
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Old 03-05-2004, 04:15 PM   #3
bryan carbon
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Default Re: Open loop fueling?

Quote:
Originally posted by Bolster
I wish I could say I totally understand everything, but that just wouldn't be true. I've got a few questions and these stem from the new UTEC 4.1 release.

1) Can someone fill me in on open loop fueling vs closed loop?

2) Will it provide '02-'03 WRX's any advantages/disadvantages?

Closed loop will allow the ECU to determine Inj. pulse width with the "tuning columns" being an offset to the maf voltage feed into the ecu. Open loop will allow the UTEC to determine Inj. pulse width through its own maf map scaled to your injector size.

The benefits of that are obviously that you can run larger injectors without a large need to "retune" a baseline for those injectors. Simplifying a bit...

Stock injectors are arguably 420cc/min. The stock ecu has a "map" which provides as a cross reference; my maf voltage vs my barometric pressure vs my temp = this ammount of air.

That is that referenced in the maf "map" or table, and the desired pulse width/on time is found, and then used to fire the injector.

The wonderful advantage of the UTEC is that you can scale larger injectors and still use this solid and consistent maf map.


If you were doing the stock inj mod it would be;

((420 / 850) - 1.0) = -50.5% global fuel adjustment.


So the map is globally adjusted removing -50.5% from the pulsewidth.


In theory anyways.
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Old 03-05-2004, 05:25 PM   #4
el~sharko
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dont listen to bryan, he has no idea what he's talking about
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Old 03-06-2004, 08:21 AM   #5
Bolster
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Bryan Carbon- thanks. I'm wondering if the values all remain the same. For instance, closed loop boost control uses a different scale of numbers (1-500), so does open loop control use the same basic values as closed loop?

Also, when I throw in a larger MAF tube (APS 70mm intake) how will I compensate, is it the same as before?
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Old 03-06-2004, 10:28 AM   #6
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Quote:
Originally posted by Bolster
Bryan Carbon- thanks. I'm wondering if the values all remain the same. For instance, closed loop boost control uses a different scale of numbers (1-500), so does open loop control use the same basic values as closed loop?

Also, when I throw in a larger MAF tube (APS 70mm intake) how will I compensate, is it the same as before?
If you use closed loop fueling and you scale your injectors in the OLF Constants you will need to remap your fuel table. Adding a larger MAF effectively scales your injectors on a mechanical side and then if you plug in X injector size on the OLF Constants you are scaling them again on the software side. With a Larger maf you should have to use a smaller injector value size to compensate for your Oversized maf mechanical correction.

Jermaine
www.turboxs.com
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Old 03-06-2004, 07:51 PM   #7
hippy
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Turboxs is calling one of the new features "feature open loop fueling", but that doesn't mean the ecu wasn't using open loop fueling b4(cause it always was under hard throttle). The problem b4 was that when the weather changed, or whatever happened, the ecu would change the hard throttle fueling(fuel trims). With the new feature, the base map will not change depending on how the car runs during closed loop fueling(partial throttle). This basically eliminates the effect of fuel trims on hard throttle fueling and gives a more stable platform to tune from. I think it also levels the playing feild at hard throttle(so different year ecu's will work the same on the same base map). The adjustmants are the same as they were b4(so far).

Compensating for something like a larger maf piping is the same as b4. You could try and enter smaller injectors then you would normally enter for the open loop settings, but I don't think it would do the pipe justice. This is all just my opinion.

peace
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Old 03-06-2004, 11:56 PM   #8
pegdrgr
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TurboXS calls this open loop fueling because that is what it is. Previously the fuel map MAF corrections were based on the fuel tables in the stock ECU. The stock ECU would run closed loop under cruising conditions, namely less than 60 % TPS, or less than 7ish PSI boost, or 5500 RPM. With the stock ECU as soon as you cross over any one of those points you would drop into a set table. Very similar to the table that the UTEC has for fuel. Basically it would reference the boost and RPM and run a predetermined injector duty cycle. The problem is the stock ECU has the ability to shift these maps to account for the environmental conditions. Since the UTEC made % changes on the MAF signal your tuned AFR would drift with these corrections. This new "feature" also known as a complete new version of firmware, allows you to run MAF corrections based on a table within the UTEC. This means as your stock ECU corrects for conditions it will not be able to shift your UTEC tuned AFR. This is a ideal step toward stand alone EM for your WRX. At this time your stock ECU is still in control of the cruise condition fuel, timing, and boost. Your stock ECU will make injector duty cycle corrections until it sees stoich at the O2 sensor.

You have a couple options for how to compensate for the larger MAF housing. You could put in a stage 2 type fuel map, and play with the injector size until you see the AFR ratio that you want to run. You could take a tuned fuel map for 3.1 and run it in the OLF mode with 420 in the injector scaling. Finally you could start with the stage 2 map, or 0 in every value for columns 10-100 and put in your actual injector size. From here you would need to build a new fuel map just like you would have for the old firmware. Those are your three options. The good news is if your 0% column is not that stable you will have greater success tuning your high boost map, since it will not drift with your long term and short term fuel trims.

The performance of the car will not depend on which choice you make, they are three different ways of accomplishing the same goal. There are obvious implications for future tuning based on which choice you make. Should you decide, option 3, to make a fuel map that matches your exact setup you will be able to add new injectors with little trouble, since you will just have to put the new injector size in the scale. That being said you will still have to tune your 0% column to try and keep you fuel trims near zero.
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