Page 1 of 2 12 LastLast
Results 1 to 20 of 33

Thread: boost bypass control??

  1. #1
    Tuner in Training
    Join Date
    Jun 2017
    Posts
    47

    boost bypass control??

    so i have been tuning my 2012 audi a7 since around november. car runs consistently 7.4s in 1/8 and 11.4-11.5s in 1/4. but i can not for the life of me figure out which table or tables control the boost bypass exactly. most times the bypass only closes (o%) when it shifts into 5th gear at top of pull. most of the pass it is around 5-15% open. commanded tq is around 750nm. if i change the airflow table to lets say 850. car just goes into limp mode and basically shuts down. any insight into this would be greatly appreciated. i just changed a bunch of stuff on the car and will need to redo the entire tune, so having a solid knowledge of this is a must at this point. i have added the tune and a 1/8 mile and 1/4 mile pull. as you can see, on this 1/4 mile pull the bypass opened alot causing boost to drop and my meth to turn off completely. thats why the lean issue and knock came in. thank you for your help
    Last edited by Hemithis01; 05-20-2020 at 10:11 AM.

  2. #2
    Tuner in Training
    Join Date
    Jun 2017
    Posts
    47
    So 22 people have looked at this and not one contribution? Has no one figured out full control of this system yet?

  3. #3
    Cant tell you which table to adjust but if it is the same as the N75 on the Turbo cars 0% is wide open 100% is closed.

  4. #4
    Tuner in Training
    Join Date
    Jun 2017
    Posts
    47
    Ok so thanks to tyler coming to the rescue again!!! He has helped me a lot over the last few days. So there is not one single table that controls the boost bypass. It is controlled by the amount of torque requested vs actual torque. The ecu regulates the bypass to hit requested torque. So if your actual tq is higher than your requested tq. The ecu opens the bypass to try and lower actual tq output. If your not hitting the requested tq limit, then the ecu closes bypass in attempt to hit requested tq. If your actual tq is much higher than requested, the car will go into limp mode.

  5. #5
    Quote Originally Posted by Hemithis01 View Post
    Ok so thanks to tyler coming to the rescue again!!! He has helped me a lot over the last few days. So there is not one single table that controls the boost bypass. It is controlled by the amount of torque requested vs actual torque. The ecu regulates the bypass to hit requested torque. So if your actual tq is higher than your requested tq. The ecu opens the bypass to try and lower actual tq output. If your not hitting the requested tq limit, then the ecu closes bypass in attempt to hit requested tq. If your actual tq is much higher than requested, the car will go into limp mode.
    Technically the effective area and predicted angle have direct control, but you shouldnt modify those unless you change the bypass out.
    Air control ultimately comes from torque control, and thats the best way to tune it.

    What the ECU is doing is controlling the bypass as a second throttle, designed to control the manifold pressure directly by venting excess out.
    So the best way to control it, is to control what it desires as manifold pressure, which is all via torque control
    If its not broke, just give it time.

  6. #6
    Tuner in Training
    Join Date
    Jun 2017
    Posts
    47
    Quote Originally Posted by Steven@HPTuners View Post
    Technically the effective area and predicted angle have direct control, but you shouldnt modify those unless you change the bypass out.
    Air control ultimately comes from torque control, and thats the best way to tune it.

    What the ECU is doing is controlling the bypass as a second throttle, designed to control the manifold pressure directly by venting excess out.
    So the best way to control it, is to control what it desires as manifold pressure, which is all via torque control
    so am i right in thinking the torque model maps are actual and requested tq? aircharge to tq table would be actual tq and tq to aircharge table would be requested tq? if i look at that way, the number seems to make more sense.

  7. #7
    Quote Originally Posted by Hemithis01 View Post
    so am i right in thinking the torque model maps are actual and requested tq? aircharge to tq table would be actual tq and tq to aircharge table would be requested tq? if i look at that way, the number seems to make more sense.
    Yessir.
    Almost all modern torque based ECUs function similarly! You get a torque request, its converted to an aircharge request, which is converted to a MAP request, which becomes the driving force behind throttle/bypass/wastegate controls. Of course thats grossly simplified because they all do it slightly differently, but in this case, you're dead on.

    The Actual Torque is estimated based on what it believes the aircharge to be using that table. This aircharge can be from a MAP sensor (via speed density), MAF sensor, or some combination. The Requested Torque is what is fed into the Tq to Aircharge table to get a desired aircharge. This then goes through an "inverse" speed density equation to get a desired MAP used to control the the necessary actuators.
    If its not broke, just give it time.

  8. #8
    Tuner in Training
    Join Date
    Jun 2017
    Posts
    47
    Quote Originally Posted by Steven@HPTuners View Post
    Yessir.
    Almost all modern torque based ECUs function similarly! You get a torque request, its converted to an aircharge request, which is converted to a MAP request, which becomes the driving force behind throttle/bypass/wastegate controls. Of course thats grossly simplified because they all do it slightly differently, but in this case, you're dead on.

    The Actual Torque is estimated based on what it believes the aircharge to be using that table. This aircharge can be from a MAP sensor (via speed density), MAF sensor, or some combination. The Requested Torque is what is fed into the Tq to Aircharge table to get a desired aircharge. This then goes through an "inverse" speed density equation to get a desired MAP used to control the the necessary actuators.
    Thank you for the simplifying that for me. Lol do you know exactly what the supercharger airflow table co trol and how to dial it in? What pids would you datalog for that table? I have tried adjusting it up and down but i can not figure out exactly what it controls. Thanks

  9. #9
    Potential Tuner
    Join Date
    May 2020
    Posts
    3
    Hemithis your tune is labeled new throttle body . Did you put a 80mm body on your car? I?m currently running an S5 with 3.33 ratio pullies. At 4500 feet elevation I can?t get more than about 195kpa absolute manifold pressure with 0 opening on the bypass valve. I?m also struggling to get the tune to give the car any ignition timing. How did you get so much advance on your tune

  10. #10
    Tuner in Training
    Join Date
    Jun 2017
    Posts
    47
    Quote Originally Posted by jacep View Post
    Hemithis your tune is labeled new throttle body . Did you put a 80mm body on your car? I?m currently running an S5 with 3.33 ratio pullies. At 4500 feet elevation I can?t get more than about 195kpa absolute manifold pressure with 0 opening on the bypass valve. I?m also struggling to get the tune to give the car any ignition timing. How did you get so much advance on your tune
    i have a audi 82mm throttle body on car now. post up your file and a log and ill see if i can help. im not a master at these cars but my car runs really well for what it is. and there is still more in it once i figure the bypass control out.

  11. #11
    Quote Originally Posted by Hemithis01 View Post
    Thank you for the simplifying that for me. Lol do you know exactly what the supercharger airflow table co trol and how to dial it in? What pids would you datalog for that table? I have tried adjusting it up and down but i can not figure out exactly what it controls. Thanks
    Its used to help estimate the airflow the car expects in the intake manifold based on supercharger characteristics.
    This value helps directly control the bypass valve, as well as help detect if the bypass valve is stuck.

    Basically, it looks up what the expected airflow is out of the supercharger based on that table. The RPM input is your engine RPM * the supercharger pulley ratio. The Pressure Ratio input is based on the pressure sensor readings (or inferred pressure if not present based on other models).
    Then it says "This is the airflow the supercharger is GOING to make". It compares this to the airflow currently desired and uses that to control the bypass.

    So roughly, its like this:
    Your current torque desired says we need 15lb/min of air. The supercharger airflow according to the table would provide 21lb/min of air. It then controls the bypass valve based on the values you have in the bypass area and angle to bleed 6lb/min of air out of the manifold.

    Hopefully that makes sense.
    If its not broke, just give it time.

  12. #12
    Potential Tuner
    Join Date
    May 2020
    Posts
    3
    Quote Originally Posted by Hemithis01 View Post
    i have a audi 82mm throttle body on car now. post up your file and a log and ill see if i can help. im not a master at these cars but my car runs really well for what it is. and there is still more in it once i figure the bypass control out.
    test 3.hptt3.hplt3a.hpl

    Here are two logs both from the same tune. The Tranny has torque limits of around (575nm guessing) that are killing me. you can see it in the one log with how much the bypass blips at the gearshift on one log. Interesting enough both logs were done almost back to back. The ECU logged nearly 100 nm more torque from one pull to the next. Acceleration seams the same, Also Dragy doesn't show any different acceleration.

    Was your TB plug and play or did you build a wire harness adapter? I played with a MB throttle body on some DIM sport software a while back but never got anywhere. I have been wanting to try the Mopar 80mm with hp tuners and see where that takes me.

  13. #13
    Tuner in Training
    Join Date
    Jun 2017
    Posts
    47
    Quote Originally Posted by Steven@HPTuners View Post
    Its used to help estimate the airflow the car expects in the intake manifold based on supercharger characteristics.
    This value helps directly control the bypass valve, as well as help detect if the bypass valve is stuck.

    Basically, it looks up what the expected airflow is out of the supercharger based on that table. The RPM input is your engine RPM * the supercharger pulley ratio. The Pressure Ratio input is based on the pressure sensor readings (or inferred pressure if not present based on other models).
    Then it says "This is the airflow the supercharger is GOING to make". It compares this to the airflow currently desired and uses that to control the bypass.

    So roughly, its like this:
    Your current torque desired says we need 15lb/min of air. The supercharger airflow according to the table would provide 21lb/min of air. It then controls the bypass valve based on the values you have in the bypass area and angle to bleed 6lb/min of air out of the manifold.

    Hopefully that makes sense.
    so if i reduced the table, it should tell the ecu the supercharger will not move as much air and in turn close bypass more and try to create more boost? does that sound correct?

  14. #14
    Quote Originally Posted by Hemithis01 View Post
    so if i reduced the table, it should tell the ecu the supercharger will not move as much air and in turn close bypass more and try to create more boost? does that sound correct?
    It should, but some diagnostic system may detect somethings up if stuff starts to not add up, so I usually try to make things as close as I can. If you want more boost, ask for more torque
    If you've changed up the supercharger though, modifying that definitely becomes necessary.
    If its not broke, just give it time.

  15. #15
    Tuner in Training
    Join Date
    Jun 2017
    Posts
    47
    Quote Originally Posted by Steven@HPTuners View Post
    It should, but some diagnostic system may detect somethings up if stuff starts to not add up, so I usually try to make things as close as I can. If you want more boost, ask for more torque
    If you've changed up the supercharger though, modifying that definitely becomes necessary.
    Asking for more tq is my biggest problem. I dont know why im having so much trouble understanding how exactly to do it. I have tried raising both tables but car either goes into limp mode or drives like garbage. I have tried changing the aircharge table axis of 750nm to as much as 850 and raising tq table as well with no luck. I have made both tables inverse of one another and still no luck. The way i Have it now is the best i have been able to get it but it drives me crazy knowing there is more left and i can't figure it out. Lol

  16. #16
    Tuner
    Join Date
    Jul 2019
    Location
    Wilmington, MA, USA
    Posts
    141
    Do you have a fault code related to it going into limp mode?

    Looking at your tune vs. stock for my '14 (attached), I don't know if I'm really qualified to speak to torque issues, but do see some issues with lambda and MAP.

    First, in your ECM 29481 table "Supercharger pressure ratio limit vs. RPM and IAT", the first two columns (1000 and 2000 RPM) have values way lower than on my stock map - yours has 1.56 in all those cells, mine has 2.24. That could make the computer think it's "overboosting" somewhere in the 1000-3000 RPM range.

    Also both your "base lambda target" tables (29210 and 29211) have 1.000 in all the cells. Your full-load table is richer than stock, but the 1.0 values in much of that table where stock is richer could have it running leaner than intended when not at full throttle. Also your "Component protection minimum lambda" table (29222) has values that are in some cases the same as in your full-load lambda table. I'd think you'd want a little "buffer" there in case lambda goes a little richer than it's supposed to. In my stock file, the values in the "minimum" table are 0.700 with the lowest full-load target being 0.900 so there's some "wiggle room" between the two.
    Attached Files Attached Files

  17. #17
    Tuner in Training
    Join Date
    Jun 2017
    Posts
    47
    You are correct on all of that. I have my temp control set that way so it doesnt go any richer than that. As for the pressure ratio i have since adjusted that more. I have the car driving amazing. Just cant get it to command more than 20ish psi boost and get bypass to close completely. Car only goes into limp when i try to command more tq amd go wide open. Other than that, car drives great.

  18. #18
    Tuner
    Join Date
    Jul 2019
    Location
    Wilmington, MA, USA
    Posts
    141
    Dumb question: do you know the max value the MAP sensors can read?

    2.5 bar sensors can register a max boost of about 21.75 PSI at sea level and I think that drops with increasing altitude. If the limit on the sensors is 2.5 bars, the CPU may see MAF increasing but MAP not and flag an error.

  19. #19
    Tuner
    Join Date
    Jul 2019
    Location
    Wilmington, MA, USA
    Posts
    141
    Looking at your tune I just realized something else... I'm not sure whether it can cause limp mode but it's definitely messed up.

    Your ECM 29480 table "Supercharger volumetric airflow vs. sc pressure ratio vs. sc RPM" seems to have several problems. First with the pulley ratio you're running, the supercharger RPM will be 23,544 at an engine RPM of 7,200... higher of course if you spin the engine faster. But the supercharger RPM axis in your table stops at the stock value of 18,000... that's a big difference!

    Likewise, the highest pressure ratio in your table is 2.10 (same as stock, at least on my car) which corresponds to a boost of about 16 PSI (at sea level). As you indicated, you're running a lot more boost than that!

    So you might try making some tweaks to that table and see if it helps.

  20. #20
    Tuner in Training
    Join Date
    Jun 2017
    Posts
    47
    Quote Originally Posted by ELaw View Post
    Dumb question: do you know the max value the MAP sensors can read?

    2.5 bar sensors can register a max boost of about 21.75 PSI at sea level and I think that drops with increasing altitude. If the limit on the sensors is 2.5 bars, the CPU may see MAF increasing but MAP not and flag an error.
    yes i understand that the map sensors go to roughly 22psi but many have run more than that on stock map sesnors. i do have 3 bar map sensors that im going to put in and recalibrate tune for. i just have not gotten around to it yet. not sure how it work as i can not find anyone who has tried it before on our cars. so ill give it a try and see how it goes.