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Old 03-01-2010, 04:12 AM   #1
Green7mgte
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Default AFR understanding

AFR understanding:
my pieces are starting to fall into place and thus beginning my build.
but as always before I remove one screw on my supra I iron out all the details of the job ahead. One thing I'm most concerned about is understanding Air to fuel ratio in the 7mgte, along with modifying timing. I would just like some feedback, link to sources and info pages for this mater. So I can go into my build with a good knowledgeable background to fall onto, once I start to tune.

thanks for the assistance in pointing me in the right direction.

just a couple general questions
what is the afr goal for at cruise? what about under boost with the karman type NA engines.
is a tad on the rich side a safer buffer? if so by how much?
is regular tested gass fine? since ive been running it forever? or would you recommend the high test pump gass?

also, just a quick question about safc1 tuning
ive read about the high and low throttle points. each setting is different per your build i understand.
is the afr tied into the open loop vs closed loop throttle setting? just a bit boggled on that part.
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Old 03-03-2010, 04:45 AM   #2
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I will get back to you on this soon, I promise... Just been VERY busy.

Let's start with this though:

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You cannot adjust the AFR for upper-mid loads or throttle less than about 70% (or 2.70v at the TPS). In order to do so you would need to force the ECU into open loop operation full time and I don't recommend it except under special circumstances... the potential benefits are too small to justify the potential headaches.
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Old 03-03-2010, 04:49 AM   #3
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very informative on that landscape.
im just trying to figure out the tuning aspect of it all. Im dead scared to put my afm on it and burn the crap outa my engine.
my wideband will be ordered tomorrow and hopefully comes next week.
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Old 03-03-2010, 04:58 AM   #4
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Well, don't do anything to force the ECU into open loop operation full time (like removing or disconnecting the stock O2 sensor) and keep the low range zeroed out and the ECU will maintain a safe AFR. If anything you may richen up the mids a bit but the ECU will pull fuel to keep the AFR at 14.7 most of the time.

That graphic is a handy reference, but it's not an absolute representation of the best tune for every application; Still, it is a good guide and the numbers are safe.
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Old 03-03-2010, 05:17 AM   #5
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as of right now my safc low throttle is set to 10 and high at 50
that was its default setting. makes sense.. closed loop from 10% to 50%. anything after half throttle and im trying to put on speed so opened loop it is. i assume.
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Old 03-05-2010, 03:56 AM   #6
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Open loop is when the ECU stops trying to adjust fueling to achieve a certain AFR (usually 14.7:1)... this is around 70% throttle or 2.70v. Trying to tune for any other AFR prior to that point will at best have no effect and at worst cause AFM related error codes and driveability issues. Generally I don't think you'll have driveability issues unless you're using another system which actively alters the fueling to achieve a set AFR such as the MAFT Pro, but it's best to just avoid the headaches. If you want a little overlap go easy on the enrichment you give it over stock and set the throttle level a good higher (try low 60's or above).

There are a few other cases where the ECU operates in open loop (such as high engine loads at lower throttle; like when you start boosting hard at half throttle going up a hill), but as the system operates most of the time in closed loop you should tune with that in mind with the low and mid loads and their set points.
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