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Old Fri, Oct-11-2013, 05:23:50 PM   #1
SliM3
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Default Fuel Adaptations Explained

The purpose of this thread is to provide detailed information on MSS54/HP fuel adaptations and a few methods of adjusting when they are applied, and/or how to disable them completely. So without further ado, let's get started.

Injection quantity is affected by the additive and multiplicative adaptations so that lambda controller corrections are kept to a minimum. This also provides a method of turning-off the lambda controller when lambda values are adjusted to equal 1.00. Through the use of adaptations, component aging and manufacturing tolerances can also be compensated for.

The multiplicative factor is applied at high air flow rates and load. The additive values affect low air flow rates and speed, also compensating for any air leaks that might be present.

There are a few conditions that must be met in order for adaptations to be enabled. These are inclusive conditions, however, all of them don't necessarily have to be active in order for adaptations to be enabled:
  • Lambda controller active
  • Engine temperature threshold is exceeded; 156F to 212F
  • Intake air temperature is below 167F
  • The load is less than KL_LAA_N threshold (see below)
  • No adaptation diagnostic error flag
  • Tank vent valve closed


Short Term Fuel Trims (STFT; Additive)
The compensation values for STFT's are +/-30%, with 1.00 equal to 14.7 or 1.00 lambda (ie. 1.00 + 0.30 = 1.30 / 1.00 - 0.30 = 0.70). They are applied at loads up to 1200rpm and 40kg/h as shown in the maps below:


In order to disable STFT's you have to set the values to 0.00 in both the minimum and maximum lambda factors.

If you want to adjust when they are applied, naturally you'd have change the Lambda Adaptation air-mass and engine speed values. My suggestion is to keep the OEM settings, as these are particularly useful if you're running larger injectors, and can better compensate at idle and off-idle loads.


Long Term Fuel Trims (LTFT; Multiplicative)
The compensation values for LTFT's are +/-25%, with 1.00 equal to 14.7 or 1.00 lambda (ie. 1.00 + 0.25 = 1.25 / 1.00 - 0.25 = 0.75). They are applied at loads above 40kg/h and 0.20rf as shown in the maps below:


The same method above also applies to disabling LTFT's; by setting the minimum/maximum factors to 0.00. Another method is to simply change the Lambda Adaptation air-mass and rf load values so that LTFT's are never applied at any load point (ie. changing air-mass to 1300kg/h and rf load to 1.5). Basically the engine will most likely never hit 1300kg/h or 1.5rf thus adaptations will never be actively applied, unless the engine miraculously exceeds these points.

Now, if you want to keep the adaptation functions you can choose the threshold at which they are active by adjusting the Lambda Adaptation_Engine Speed function. Normally the load is set to 1.5rf, therefore, adaptations are active at all load points up to 1.5rf for each respective rpm point. The inherent problem with this high threshold is that fuel trim is also applied to your full-load fuel map, and can cause lean conditions at high rpm's. I have mine set to be active up to 0.30rf which is right around cruise. Perfect!!



I'll probably add more info to this thread, but this is pretty much the gist of how and when adaptations are applied.
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- Checksum corrections for modified DME partial & full bin files

- CSL SMG Engine Parameters (DME) by Slim

- Fuel adaptations explained

- Checksum Verification
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Old Fri, Oct-11-2013, 08:44:53 PM   #2
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Default Re: Fuel Adaptations Explained

Quote:
Originally Posted by SliM3 View Post
I'll probably add more info to this thread, but this is pretty much the gist of how and when adaptations are applied.
Fantastic explanation, I can honestly say I learned even more about the mechanisms employed by the DME as a result of what you've shared - I've always been hesitant on which value to modify and how far I could reasonably go.

Cheers!
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Old Fri, Oct-11-2013, 09:23:41 PM   #3
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Default Re: Fuel Adaptations Explained

If load is used to determine trims how is alpha-n determining engine load? or does it simply use the o2. sensor alone? I'll have to check my values with INPA as I'm running alpha-n. I recall the long term value(s) can indicate a general trend by the DME to correct lean / rich running conditions, either due to low fuel pressure, dirty air cleaner etc?
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Old Fri, Oct-11-2013, 11:07:13 PM   #4
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Default Re: Fuel Adaptations Explained

In alpha-n mode, the DME still calculates load by taking into account air pressure, throttle position, RPM, and IAT.
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Old Sat, Oct-12-2013, 02:25:40 PM   #5
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Default Re: Fuel Adaptations Explained

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Originally Posted by SliM3 View Post
Now, if you want to keep the adaptation functions you can choose the threshold at which they are active by adjusting the Lambda Adaptation_Engine Speed function.
This is a great tip Sli.

I have posted before that I found gains from curtailed limits (not disabled completely) on adaptations, based on the hypothesis that when I've been stuck in slow low-load conditions (also known as "bad traffic") for long periods, the adaptation goes very lean and then doesn't re-adapt fast enough to respond to short periods when you can 'get on it'.

So you've set .3rf for the whole range... any thought to pros/cons of varying the load across RPM ranges?

Think I'm going to re-enable my adaptation error codes and try this out this afternoon...
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Old Sat, Oct-12-2013, 03:52:10 PM   #6
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Default Re: Fuel Adaptations Explained

Is there somewhere to change the target air fuel? I ask because during idle an cruising light throttle my air fuels always try to stay around high 15's sometimes low 16's. It runs fine and I don't get detonation at these light loads and great gas mileage. But I'd like to make it more stoich at 14.7. I've played with the multiplactive and additive values but it doesn't seem to have any effect. Anyway you can send me a xdf where I can adjust the reference load and airmass? Mines only has the other tables available(Min/Max tables)

Tom
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Last edited by Tchleung; Sat, Oct-12-2013 at 04:02:39 PM.
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Old Sat, Oct-12-2013, 04:23:07 PM   #7
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Default Re: Fuel Adaptations Explained

SOOO............. I just noticed now my tune has the "Lambda Adapatation Minimum Engine Temperature" set to 100*C(212*F) where as stock is 69*(156*F) My car NEVER reached 212*F coolant temperatures. Wtf? So maybe that's why my fuel trim adaptions have not been doing anything. It still thinks it's in warm up mode?
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Old Sat, Oct-12-2013, 06:22:46 PM   #8
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Default Re: Fuel Adaptations Explained

Sli,

We really needed this so thanks. What would be the best setting, just set 0.00 for all?? And what is the difference between additive 1 and 2?

These are mine


Last edited by M3CARBON1; Sat, Oct-12-2013 at 07:08:23 PM.
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Old Sat, Oct-12-2013, 10:53:16 PM   #9
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Default Re: Fuel Adaptations Explained

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Originally Posted by M3CARBON1 View Post
And what is the difference between additive 1 and 2?
I would assume Bank 1 and bank 2
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Old Sun, Oct-13-2013, 06:50:35 PM   #10
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Default Re: Fuel Adaptations Explained

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Originally Posted by Tchleung View Post
I would assume Bank 1 and bank 2
So depending on the health of the sensor each bank could have a different reading?!
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Discussing Fuel Adaptations Explained in the Coding and Tuning Forum - Discuss all avenues of coding and tuning here! at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)