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Thread: Fuel dynamics mafless?

  1. #1
    Lifetime Member hymey's Avatar
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    Default Fuel dynamics mafless?

    Still having the same ole issues with dynamics(accelerator pump). Put simply it doesnt work mafless. With the maf on I can command higher numbers in B2005 and I can get a lot more fuel in throttle tip in. With SD tune it doesn't respond at all. With the stock cam it wasn't to bad...but it is noticable with a bigger cam installed and manual transmission. I am aware of several cars that have the issue. Even including one with vcm suite. With the MAF on it's fine but I have an OTR now and with the MAF in place there is reversion issues and the MAF is much more sensitive directly in front of the TB.

    Basically if I am driving through traffic and apply throttle there is a small surge that occurs less then half a second. With the same scenario MAF on it generally wheel spins(as B2005 is working). If racing at the drags its even worse with a delay between shifts. Disabling CFCO and DFCO doesn't help. Nor just richening the VE in problematic areas. Hopefully we can get a patch and get dynamics working correctly. Something that needs working on.

    Joel

  2. #2
    Lifetime Member hymey's Avatar
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    Did some more testing today. Swingtan has spent some time sorting through my tune and I have too, but Simon made some adjustments to my tune to other tables under dynamics and its a lot better now. What's required with a MAF tune is different then that of a SD tune by a long shot. Also settings are more critical with a manual gearbox because of shifting.

    B2002 and B2003. The values are reversed. This is a table for when fuel begins to decay after fast throttle transitions. I tried this initially it didn't appear to help. B2005 was another I tried, it worked but was slow to respond. B2011 is what I believe that made a considerable difference. Also use B0148 open loop table to your advantage to creep up on PE.

    Simon has done countless hours on going through this. A big thanks to him. I only touched on half of it. The settings in the tune are perfect and I would even doubt most workshops would have done the research in e38 tuning to the extent of Simon. We have shared ideas over the past 11 months or so and have gone leaps and bounds.

  3. #3
    Lifetime Member swingtan's Avatar
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    Hi Joel,

    Glad to see the changes had a positive effect. I'm still working on fine tuning them though and have a thought on what may be happening. I need to log a heap more data and see what goes but I think I'm on the right track. I've just been fixing a slight hesitation I get in 6th when cresting a hill that was a bit annoying but again I think I've got that one sorted as well.

    Simon

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    Lifetime Member Tre-Cool's Avatar
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    Hey Simon, do you have any more experiance you can share on this matter?

    I've retuned a mates Twin Turbo VE and from the logs at the drags and street it gets lean between the shifts and i believe because of this i start registering knock in 4th. (all other gears are ok)

    I will upload logs and tune when i get home tonight, if i cant get it to work my only other option is to put the maf back on and i don't really want to have to do that. :-(

  5. #5
    Forum tyhee Site Admin GMPX's Avatar
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    Nice to see you guys diving so deep in to this, I must confess I've forgotten a lot of the tables already, my hands smell of Diesel these days
    Need official EFILive help, please go here.
    For tuning support please post your questions on this forum (or other auto forums).
    Sorry if I don't respond to your PM, don't take it personal.


  6. #6
    Lifetime Member swingtan's Avatar
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    OK, here's where I got to with Dynamics and MAFless......

    For the record, I've tried full OL-SD, OL-MAF and CL-MAF. All were tested over a considerable period of time each, with at least 3 or 4 months of driving in each mode. OL-SD was run for around a year while looking at many different settings. The current mode, CL-MAF is what I'll be staying with for now as I find it gives the best "all round" results for the driving that I do.

    Ok, on to dynamics...

    My View On Dynamics
    Delving into the settings and how the amount of dynamic fuel was calculated, I came to the conclusion that dynamics and MAF measured airflow went hand in hand. The main table involved here is B2013, "Impact Factor, Airflow", this being a "Factor" effects the final calculation for dynamic fueling.

    B2013 uses "Airflow ( gm/Sec in my case )" to provide a multiplier for the final amount of "dynamic" fuel to add when stomping on the throttle. If the MAF is disabled, then the table will always read "0 gm/Sec" and use that figure for all dynamic fueling calculations. There is no way to do fine tuning of the dynamics in this case because the airflow will never change.

    OL-SD
    In this mode, I found that the dynamics were a very fickle setting. They were sometimes working well and other times way too rich or too lean. This was where my views on B2013 really came from. I could set the dymanics up to work well for stomping on the throttle and moving up through the gears, but then had rich spikes when just cruising around. If I got the cruise settings working well, then I was lean if I gave it a bit. This resulted in a rough feeling change that felt like the car hesitated slightly when getting back on the throttle after a gear change.

    My views on this are that you have 4 options....
    1. Set the dynamics up for WOT and live with the richness when cruising. This would be fine if you do a lot of track work or have a specific track only car / tune.
    2. Set the dynamics up for cruising, and live with the roughness of the gear change. If you really wanted, you could flat change between gears and hope you don't miss shift.........
    3. Set the dynamics up as a mix of both and be stuck in a position where neither is optimal, but neither is way off. It would be like getting some of the worst of both without really getting any of the good points though.
    4. Set the dynamics up for WOT and get an auto :p


    So my thoughts were that while OL-SD worked very well for me most of the time, the dynamics issues were enough for me to go looking for something better.

    OL-MAF
    Enter the OL-MAF era. Given my thoughts on the MAF being the key to controlling the dynamics, I figured I should turn it back on and see how things went. After a year of OL-SD tuning, it took a very, very short time to dial in the MAF and get the dynamics close to perfect. With the MAF signal back and B2013 adjusted, I was able to control how much dynamic fuel was being applied. It was quite easy add more or less by looking as the MAF signal and the WB-O2 together. Shifts were noticeably better across the board and the car was more "fun" to drive. 0-100KMH times were on par with OL-SD and the best economy was achieved at 8.6Lt/100km or 26mpg. At this time I was also playing with lean cruise and seeing how things worked out there.

    CL-MAF

    On to CL-MAF, where some interesting results were observed. I originally went back to CL to work on some light throttle, low speed surging I had. I soon found that CL mode had some other benefits that helped dynamics, specifically with throttle close. Many people are only concerned with the initial stomp, to get the best power out of the motor. Not many care about the throttle close, but this can have significant effects on gear changes in a manual.

    For example, if you go very rich on throttle close, than stomp on the throttle again for the next gear, you may end up way too rich and flood the motor for a second. This could see a hesitation in the motor as the clutch is let out making the change feel rough.

    When the STFT's were turned back on, they helped control the return to "stoich" for the fueling. This helped control dynamic fueling on throttle close, not only on gear change but any time the ECM went back into CL mode after being in PE mode. The WB-O2 showed a much faster return to stoich than when STFT's were not being used.

    I mentioned "lean cruise" earlier and should mention something about that, though it is a bit OT to dynamics. I think that lean cruise is a bit of a "misnomer" in the E38 - Gen IV due to the way the engine makes power. While the car can run fine at 15.5:1 AFR, it feels stronger if it runs a little richer. I've played with PE settings and found the car to pull up hills better when...

    [list][*]lean cruise is active at 15.5:1 afr.[*]there is no change in the throttle possition[*]the ECM detects a rise in MAP readings and enables PE mode[*]commanded mixture becomes 13:1
    [list]

    The idea I have is that while you can run a leaner mixture, the engine will produce less power. This results in you using more throttle and therefore, more fuel. Running slightly richer results in a little more power, so you use less throttle.... The end result is that the final economy figures for both are similar, but the car feels more "effortless" when running a tad richer.

    I just got back from a trip to Eden New South Wales, while towing a very full trailer. Running CL-MAF, I got a total average of 12.8Lt/100KM @ 98kmh, or 17.8mpg. That was a pretty good result given the size of the trailer.

    Simon.

  7. #7
    Lifetime Member hymey's Avatar
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    As I discussed with you Tre, Fuel dynamics needs a lot of work mafless and differs from engine to engine. I have even changed intakes and it upset the settings.

    FI is a much different ball game, I am lucky enough to have nutted it out, The impact tables need to be increased A LOT past 100kpa. So when you shift fast boost comes up really quickly it needs the fuel to support it. If you aren't seeing vampire teeth in the logs you need to increase it, if still lean increase it more. It will end up very steep looking. The beauty of FI is below 100kpa will be stock, above 100kpa is where the changes occur, dont be scared to add a lot more in, the car will feel a lot more aggressive on gear changes and you will end up busting donuts like I just did this afternoon

    BUT after you get it right the VE may need reducing slightly. This is where road/track tuning the e38 is so more important then dyno tuning.

    Look at B2012. Try setting values from 104+ IVT and from 100-200 kpa to around 0.35 to 0.4 start with 0.4 you will see positive results.

    cheers

    Joel

  8. #8
    Lifetime Member Tre-Cool's Avatar
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    Cheers for the feedback fella's.

    I initially did increase some of the tables, however it appears i didnt get them all or increase them enough. I remember from the fastest log of the night that there was almost no lean out in the first 2 gear changes (1-2-3) but the 4th resulted in a much larger "lean-out". (I dont tend to lift completly on shifts at the drags, but i dont keep my foot buried either)

    it's good to get other peopels experiance/knowledge on this matter, as i suspect my brother's tt will have a similar issue, so i will be able to make the required changes when it comes back to me.

  9. #9
    Lifetime Member swingtan's Avatar
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    This is why retaining the MAF helps ( unless of course you are running FI or a big overlap cam ). You can get the dynamics a lot closer.

    The other trick I did for gear changes, was to raise the VE table where it matches the engine conditions between gears during track use. For example, at full song, the engine RPMs are probably between 4000 RPM and 6400 RPM during the change event. At the same time, MAP is probably down around 25 or so. These conditions would rarely, if ever be met during normal driving so you can "fudge" the VE and richen it up. This helps stop the lean out between gears.

    Tuning the VE and fueling in a manual is a lot different than an auto. The gear change conditions need careful work in a manual to get nice crisp changes. Unlike an auto where the throttle stays wide open, the on - off throttle conditions in a manual need to be catered for.

    Simon.

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    I'm sorry guys I am having a hard time following this thread, I just don't
    get how you can run MAF-less with a coefficient system.

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