This will be an ongoing thread of everything that I have learned from reading the tuning section of nefmoto to further understand the ME7 Motronic system. I will start off by saying I am no expert and this document is my interpretation of everything that I have been exposed to thus far. I borrow literature and information from both the S4 Tuning Wiki as well as nefmoto forum and nothing further. I would personally like to thank Nyet, Phila_dot, prj and ddillenger (May God rest your soul) as half of the information gathered would not have been possible without these fine folks. I also want to extend my gratitude to thelastleroy for coming up with the community stage 1 and 2 threads . Please for the love of God if anything I say here is wrong tell me so I can further my learning as well!
Ok, so say you’re a rookie (like myself) and are just thrown into this deep rainforest that is ME7 with no GPS. All you have on you is a half washed away mapquest document from 2009 WYD? You scour endlessly for a rough idea of where to go next. In the spirit of Nefmoto I am not asking before I have read, I am reading before I ask and trying to get at least a basic understanding.
So where the hell do we begin this crazy adventure? How about with fueling. The tuning wiki does a great job of encompassing this so this will for the most part be me wording out what I have gathered. For the sake of simplicity I will not be getting into situations that involve modifying for larger injectors, larger fuel pressure regulator and other adjustments to the fuel system. This paper is more geared towards the individual that is just looking to do a basic Stage 1 or 2 remap with no fueling changes other than lambda request value alteration.
The first map necessary for a stage 1 tune would be LAMFA (some would argue KFLF could also be changed, but throughout my readings I have learned to not touch this map unless absolutely necessary. This map is a scaling factor for the conversion of a predicted load to relative fuel mass) . Now this map, from my understanding, is active in specific situations and have built in delays which trigger them. Specifically, LAMFA is delayed by TLAFA which is just a delay timer for LAMFA. The stock value in my file was set to 1 (According to my damos this is a measure in seconds). Changing this to zero would effectively remove the delay of the use of the LAMFA map thus it always remains active and the first determinant of fuel based operation in the ME7 fuel delivery system when requesting above 50% torque. Obviously, there can be and are many other maps that can intervene with fueling. You have internal functions which limit you to a lambda of 14.7 all the time unless there is intervention within one of the two maps (in my case) LAMFA or KFLBTS. LAMFA displays its values in lambda where 14.7 AFR equates to 1. To make this even clearer, if you go with a smaller number than 1 you will effectively be lowering your fuel request below the 14.7 mark which is richer (helps cool combustion event as well as prevent knock allowing you do make more power without the risk of damaging things). If you raise the value of 1 upwards then you are going into lean territory which can put your engine at risk for damage as the temperatures in the cylinder will increase (High EGTs can lead to component damage and knock). Don’t let the above statements fool you about a rich condition, there is such things as too rich. It is my understanding that lamda cannot be increased past a factor of 1 (14.7 AFR) as there are other systems in the ecu that prevent you from entering a lean condition (this value can possibly be a bit higher depending on cruise control system and such upon further reading). LAMFA, in my case, has an axis starting at 50% and scales all the way close to 100% but never quite reaches. It is my understanding that this axis percentage relates to requested torque. It is the consensus that LAMFA will only need lambda adjustment in the last few columns of the map as it is only in these high torque request areas that we will see larger boost numbers (load request) which requires us to richen up the mixture for reasons mentioned above.
The second map that I have seen most reputable tuning companies change would be KFLBTS. This is a map intended on component protection. I know what you’re thinking. Isn’t LAMFA enough? Think of KFLBTS as a metaphorical big brother to LAMFA. If the engine is under certain conditions (such as high EGTs) the big brother KFLBTS will come to the rescue. From reading I have noted that KFLBTS is activated not by actual EGT temperatures but through calculated EGTs that the motronic system in its infinite complexity calculates and then spits out a result. The trigger map that is involved in activating KFLBTS is TABGBTS. This map is a temperature threshold for calculated EGTs. In my file it is set at 800 degrees celcius from factory. So that means whenever the ME7 system calculates EGTs above 800 LAMFA goes to sleep and KFLBTS wakes up to deliver some further rich mixtures in an attempt to cool down the combustion chamber and lower EGTs as well as prevent knock. I have noticed that some reputable tuners actually make KFLBTS and LAMFA values in the high rpm and high load zones nearly identical, which I could see as a problem. It is my understanding to keep this table a little richer than LAMFA always so that it can actually do its job. Raising the temperature threshold from 800 to 900 or higher can mitigate the time spent in the KFLBTS as well which I have also seen examples of.
Another thing to note. These two maps are intended for WOT afr request mainly from what I gather. Once you have your WOT set to where you want it you can modify another map called KFKHFM which is an air mass correction scale factor. With this map you can adjust how much air the MAF thinks it is taking in and tune your part throttle fuel trims +/- 3 generally. The higher the values the more air the ecu thinks it is getting so it will in turn add more fuel. If you are experiencing lean values scale this number up and if you are experiencing rich values scale this number down. *(Please correct me if I am wrong)*
Finally, I would like to say that the tuning tables mentioned above are during open loop operation where the computer makes fueling adjustments according to pre-calculated data and information from maps. This will usually occur during WOT (power enrichment) conditions. The rest of the time (for the most part) the computer relies off the input from sensors such as the o2 sensors to make fueling corrections if necessary and this is called closed loop operation.
So that would be as far as I would understand the fueling system for a basic stage 1 and 2 remap. Obviously the correct way to do anything is to take logs and watch fuel trims and make sure nothing is under or overcorrecting too hard. Double, triple, quadruple check your hardware folks. You could be chasing mechanical issues for days, weeks, months if you are not careful by attempting to bandaid a very easily fixable mechanical issue such as a bad sensor or fuel filter. Take logs before you change anything and make sure nothing looks wacky when the tune is stock. There are great, free programs that can log for you right here on the forum that you can use at any time. I am still getting used to the logging process and I am sure I will have questions for some of the heavy hitters out there.
I am sure there is more that I could potentially be missing here. Could someone else chime in if I have missed something
I am currently working on boost literature and hope to have a next entry soon.