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Dwell table std and TFSI coils

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  • Dwell table std and TFSI coils

    Running Link engine management.
    This is my current dwell table as tuned a number of years ago before i owned the car. Std ADU engine, OEM coils. Any comments, good or bad?



    What should this table look like when I run TFSI coils? I've done some hunting and it looks like 2.0-2.5ms? If so should I interpolate that into the above table (i.e. 2.5 in the high areas and 2.0 in the low areas)? There are no additional 'corrections' to the above table in the Link ECU from what I can tell.

  • #2
    I think you probably want to do something a little different.

    The problem is, when you see dwell numbers on the internet, they're almost always missing one key piece of information: the voltage.

    Coil dwell is highly dependent on voltage. That's because the coil's functioning is really based on current, and as voltage decreases the current does too (Ohm's law: I=E/R) so the dwell has to be increased to compensate.

    The "2.0-2.5 ms" dwell time you found most likely does not mean it should be 2.0 at high voltage and 2.5 at low voltage because that's not enough of a range. Look at the numbers currently in your dwell table - there's about a 3:1 range from high to low voltage.

    Most likely that "2.0-2.5" figure is just an approximation, and is at normal system voltage when running which should be around 14 volts.

    So, finally getting to the point here... I'd probably just go through the entire table and multiply all the numbers by 0.8. That'll give dwell in the specified range at 14 volts (a little less at high RPM), and correspondingly higher dwell as voltage drops.
    Be alert! America needs more lerts.
    Eric Law
    '90 80Q with AAN and Megasquirt
    '97 Saab 9000 Aero: mostly stock but ECU tweaks to add fastness
    '86 4KTQ: R.I.P.

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    • #3
      That sounds pretty good to me, thanks for the suggestion.

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      • #4
        So I referred back to this thread: http://www.s2forum.com/forum/showthread.php?t=60611
        In that thread, PRJ advises 2.0 ms, and around 2.5 @ 11V. Looking at my original dwell table, it appears to be a factor of about 0.6, or 60%. This was very easy to apply to my table, as shown below:



        So the new dwell table looks like this:


        Looks OK?

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        • #5
          hows it perform. on stock coils i ran 3.1 and it was fine. lower gave me soem issue hight up the rpm.

          from reading tfsi need lower. give it a go. go up tiny bits if you get an issue.

          what link you on G4. ive only done linkplus and g3. that looks a bit newer

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          • #6
            I have Link G4 Extreme.

            On stock coils it has a misfire at max load between approx 4500 and 5500 rpm. In that range at typical system voltage of 13 to 13.5V its running dwell of around 2.6ms. Sounds like I should try increasing the dwell on the stock coils then?

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            • #7
              Just to be clear, I'm still running OEM coils. OK, I'm going to try these dwell settings and see how it goes. All fields up 25%:



              Now looks like this:

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              • #8
                That looks pretty good.

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                • #9
                  yes go up on the stock coils. i had the same on vems. at lower boost it was fine as i increased the boost i got misfires in that exact range.

                  iirc 3.1 is where it was at for a clean run through. stock were fine with stock plugs to 2 bar with that setting. didn't overheat either

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                  • #10
                    Ok thanks guys, will report back on the results.

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                    • #11
                      Update: I was still getting some hesitation at WOT using the updated dwell table above. Looking at the log just now I see the dwell dropped to about 3.15 at 4900 rpm and that's when it started to hold back. I upped it incrementally until I got a clean 3rd gear pull. It's up about 15% on the table above (std coils). On that last run the voltage was a bit lower (guess the battery was charged) at around 13.1V and it was running dwell in the high 3s during that last run. First time since I've owned this car that I've had a clean 3rd gear pull. So on the roller coaster ride of Audi ownership I'm currently on a bit of a high - I've finally got this thing going like a proper RS!

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                      • #12
                        thats good. shows the coils can take a bit more. thing the lower voltage measn you need a slightly higher setting. having said that all ecu's are different and i have found link is good but takes a fair bit of fine tuning.

                        give the coils a quick feel make sure they aint too hot.

                        its nice when they run thru clean though.

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                        • #13
                          That's a good point Gazza. What I might do is revert back to the original table except in the areas where I was having a problem before, using the most recent values for that area only. Is there a more scientific way of working this out? It's like poking around in the dark! The car is going on the dyno this Friday to see how it is performing. If there are any issues I will book it in for a retune.

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                          • #14
                            hard to be sure. im sure there is a science but not from me. my vems has nowhere near the detail of your link in that area. links are like that ive found. id feel for heat. lower the areas that you had no issue with before.

                            i found that once at about 1.4 bar or so i started to get a bit of non clean pulls, a bit of hesitation. i run a fairly big turbo bit it was towards the top of spool shall we say. so about 4500 rpm for me onwards..

                            id lower the other areas off. try to just look to change the areas that are at fault or weak rather than across the board changes. seem your into the detailed finer tuning part now. be mindful of the interpolating cells. if the problem is in one specific area you may want to change the rpm numbers on the table and have less lower rpm settings and more in the 3500-5500 range.

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                            • #15
                              I've now fitted 2.0 TFSI coils, 07K 905 715F. This is the dwell table I'm running:



                              Look reasonable? Car is running very well so far but haven't wound it up in a high gear yet.

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