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Old 04-11-2011, 04:09 AM   #1
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STFT = Lambda ... ?

This is probably painfully obvious but I'll still ask.

Is STFT equal to Lambda?

I ask because I've been adjusting the MTF trying to get everything to hit near 1. Been logging and adjusting for a few weeks now off and on and at high MAF counts I just couldn't get the STFT to go to 1. Was always something like 0.725, 0.850, ...
Tonight I turned my brain back on, I think hard to tell ya'know, and I looked at my fuel source, 5, and it hit me. I open the base fuel table and I'm looking at a target Lambda of 0.85. I flip back to my STFT log at high MAF counts and sure enough it's pretty damn close to 0.85 and the STFT only goes to that when I enter the base fuel table. So I think I'm finally understanding this crap and I got it working?

Why this didn't dawn on my before is beyond me. Seems obvious now


The only thing that's still odd, maybe, is that when it goes to the base fuel table, 5, my load goes above 1. Runs great though. But it's done this the whole time so it seems like that's how it's supposed to be. I know in one of the other threads you guy's had said my injector calibration or something else must of been off, but far as everything up to the switch to 5 is concerned it can't be; it's nearly perfect. Load at warm idle is a tic under 0.2, steady speed cruise in 5th is about 0.32 load.
Possibly the 'percent load switch' has something to do with it? I have mine set to 1.


Anyways, I have the 42# injectors working pretty damn good I think. Now I have to play with spark more and get that sorted out. I was running the SCT 'race fuel' spark map with no knock at all. But now that the fueling is closer to what it should be, or what I'm commanding, the KS is adding a bit and pulling a bit here and there. Easy fixes.


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Old 04-11-2011, 08:48 AM   #2
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You are correct , Short Turm Fuel Trim (stft) is closed loop only , If you trip into open loop the STFT/stft will show what you have commanded in your base fuel table , if you datalog the open loop flag or the fuel source as you used it will show if you changed from closed loop to open loop and will make it easy to follow

Your Percent load switch should be set to 1 which is factory

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Old 04-11-2011, 03:09 PM   #3
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Sweeet!



Bear with me here.

So if my WBO2 reads 'rich' (which is richer than 0.68 Lambda) at very high RPM's, over 6k and over 800 counts, but my STFT reads 0.85, which is what I'm commanding ... Then I should assume it's my timing that needs to be adjusted, correct?
Because firing the plug earlier would allow more burn time and bring the WBO2 back to where it should be.
Or am I thinking about this wrong?
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Old 04-11-2011, 05:39 PM   #4
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One thing Tom forgot to mention is just because your ECU is commanding .82 (for example) doesnt mean you are actually getting that. Thats why you have to use the MAF transfer function to get the two to read the same.
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Old 04-11-2011, 06:08 PM   #5
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But retarded timing can also cause the WBO2 to read rich, right?
So I have to play with both individually to find which is wrong, right?
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Old 04-11-2011, 08:07 PM   #6
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Quote:
Originally Posted by iminhell View Post
Sweeet!



Bear with me here.

So if my WBO2 reads 'rich' (which is richer than 0.68 Lambda) at very high RPM's, over 6k and over 800 counts, but my STFT reads 0.85, which is what I'm commanding ... Then I should assume it's my timing that needs to be adjusted, correct?
Because firing the plug earlier would allow more burn time and bring the WBO2 back to where it should be.
Or am I thinking about this wrong?
Not exactly if your WB reads rich then you need to change your MTF IF you have the base fuel tables set to what you want the targed to be

Set your base fuel tables to what lambda target you want then change the MTF to get the AF to match what AF/lambda you want

Timing will do little to change the AF

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Old 04-11-2011, 09:09 PM   #7
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So then I have to log my WBO2 through the XcalII analog, right?

Because if the STFT's read my target Lambda I have no other reliable way to judge how and how much to adjust the MTF.
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Old 04-11-2011, 09:19 PM   #8
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You either have to log it or watch the wide band o2 then IF you have the base fuel table set to the lambda target you want and your rich/lean on the wide band then change the MTF to get the AF you want

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Old 04-11-2011, 11:33 PM   #9
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good info here, will be using this thanks guys.
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Old 04-12-2011, 12:51 PM   #10
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Thats why you have to use the MAF transfer function to get the two to read the same.
....and I quote myself.
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