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Discussion Starter · #1 ·
I came across an idea last night about keeping a lean afr on idle, but not having to sculpt the fuel map to have a platau. It seems even with throttle accell tuned, the engine seems to somewhat stumble when coming off idle or operating at low rpm off idle. I try to keep a 14.5 - 15.5 afr to keep fuel smell down and have a nice meaty idle, but need a ~13.5 afr under any load condition due to cams and low port velocity.

Instead of leaning out vacuum under 1300 rpm on the map, I kept it rich (~13.0) and went to the Fuel Offset vs RPM table under advanced idle and put -17% all the way across to give me high 14:1s, low 15:1 at idle. Any throttle movement seems much improved in the idle range. Has any one else tuned like that and if so have you noticed any positive / negative things about it?
 
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I try to get a solid fuel/ignition map first than use any trims if necessary. The Fuel Offset Vs. RPM map is used to help keep your target idle. If your idle drfits too high/low past your set target idle this just adds/subtracts fuel to help bring it back in sync. Sounds like your success with this map is just a bandaid for another issue. How do your Accel tables look? If these aren't set correctly you will have hesistation off idle, especially with larger throttle bodies.
 

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Discussion Starter · #3 ·
I'll post some pics when I get home of the trims and map and can show you more of what I'm talking about. Timing affects idle quite a bit more than fuel, so I am only using that trim to keep idle (along with IAC closed loop).
 
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Timing affects idle quite a bit more than fuel, so I am only using that trim to keep idle (along with IAC closed loop).
I agree with you on the timing part. Thats way I use the Ignition vs Idle RPM table and not the Fuel Offset vs RPM table...
 

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Discussion Starter · #5 ·
My idle on is below ~1.9% throttle and off above ~1.1% throttle. So lets say i'm creeping up ramps in my garage, i hit 4% throttle, idle turns off and my load is where the blue arrow is at. the engine needs more then 15.4 afr to provide enough torque to not stall at that load, but it is stuck between my lean idle plateau and normal fuel requirement (blue arrow) the aem is left to average the load cells and come up with an AFR that is still not ideal. Also my throttle accel has to compensate more, going possibly over 100% of the current map pulse width to provide enough fuel. I can try to go radical on my TH accel pump (75mm TB on a 2.0l 4cyl) but it seems harder to tune drive-ability with wide swings in those tables.

Or I can make the map rich in that region (~13.0) and as soon as I enter idle (by throttle position or any other means), it leans out by the Fuel Offset table, and as soon as i exit idle it runs off the map, providing instant fuel, and i can make the Accel pump tables, sustain% and throttle filter settings less agressive since the map pulse width is higher. That way the target pulse width for the right afr is within the average of the load cells all the time, and tuning the throttle accel would be easier and not require such sensitive options.

Thats how I was thinking of it, does that make sense? Am I on the right track?

Fuel before:

Fuel now:


 

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good info, nomoreideas. though my accel settings are very close to the stock 1101 cal file i'm curious how much more i can improve on them after seeing yours. i'll post a picture of my cal file settings later tonite.

on a side note i'm stumped by the dTPS accel table. i understand how the dTPS trigger works but what exactly does the dTPS accel table effect? i have my trigger set to 5 so anytime there is a 5% change in TPS the accel/decel function will kick in and if i remember correctly my dTPS accel table is the same as what's in the 1101 cal file. whenever i blip the throttle while cruising it will usually go lean (15.5afr) before it goes rich. i am under the impression this is because of the length of intake piping in my NA-T setup so when the throttle cracks open or if there is any dTPS change then a whole lot more air is entering the motor. throttle tip in is lean to about 15.5 for just a split second before going rich for accel. but isn't that normal?
 

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Discussion Starter · #7 ·
throttle tip in is lean to about 15.5 for just a split second before going rich for accel. but isn't that normal?
Noo.. if the whole pump is set up correctly your AFR shouldnt change at all when you step on the gas, and if nothing else go a tad rich. I havent looked at the supra map (I own a MR2) but the mr2 base accel tables were junk. Since i have a large throttle body, i noticed the largest change was when i cracked the throttle just a little bit, and little change after ~12% open (which is why my Accel modifier table ramps down so much). the DTPS table is used for the difference of throttle position over a period of time (milliseconds) and matches a value in that table. If that exceeds dtps trigger, then a pump is activated.

I created the accel tables i posted in about 10 minutes. They are very far from perfect, but makes rev-matching, shifting and taking off much smoother. I still have a bit of tuning to do but this makes driving it daily much easier.
 
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