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Thread: Little bit of surge coming to a stop

  1. #1

    Little bit of surge coming to a stop

    Here is the tune file used to make the log. When coming to a stop, it surges a bit and drops idle down, but doesn't die. It also still hangs in park if I rev it. So I imagine they are related to the same airflow issue.

    Any suggestions?

    Btw, this is my wideband cfg, but it wasn't hooked up. So it just shows a flat AFR across the board.

    Mods:
    02 Trans Am
    EPS 234/242 111+3 Cam
    TEA Stage 2 LS6 Heads
    FAST 102 Manifold and FAST 102 TB
    TSP 100mm MAF with the LS3 Cartridge (disabled - only using the IAT)
    Kooks 1-7/8" LT Headers and 3" True Duals
    Bosch EV14 52lbs Injectors with data from FIC
    Racetronix Pump & new WIX Fuel Filter
    FLT Level 6 4L60E
    CircleD 2E 4200 Stall Converter
    BeCool Aluminum Radiator with 160 T-Stat
    New Delphi MAP relocated to front of FAST
    New IAC Motor
    OLSD Tune
    Ballenger AFR500 Wideband
    Attached Files Attached Files
    Last edited by JakeFusion; 10-16-2014 at 09:59 PM.

  2. #2
    Is this an airflow issue with my base running airflow table? Or is it a cracker/follower issue?

  3. #3
    Senior Tuner
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    The cracker looks relatively sane. The RPM is showing a
    slow oscillation as you roll down the road speed. I think
    maybe you don't need as much cracker at higher RPMs,
    but whether this has anything to do with the behavior,
    I do not know. But it seems that as you approach 0 MPH
    you are applying a changing airflow "bias" that the RPM
    loop has to react to. If there is instability, there could
    be "amplification".

    I do see your spark advance pulling back to 28 degrees
    from 40+, before it all starts up. I have always found the
    idle instability seems to relate to the motor being "soggy".
    I think over-rich mixture is likely the cause, but lower
    timing also aggravates it.

    Your over/underspeed tables look OK but maybe can't
    stabilize it. I think for diagnostic purposes I'd disable
    them and try to tune in idle stability with none of their
    "help". They can obscure the amount of trouble you really
    have holding stable idle.

    Now what little I know about PID controllers, and have
    played with a bit in the idle stability chase, makes me think
    your idle RPM loop params (P, I, D) want some work if you
    can't get it clean by mixture and spark. I see that your
    D coefficients are zero, at low error and then pop up.
    This could make the derivative correction (a) do nothing
    until large error is seen and (b) act "notchy" with a dead
    band. These can set up hysteretic oscillation I believe
    (like how you can make a cheap oscillator with a Schmitt
    trigger inverter and a RC feedback). I prefer to see the
    D factors applied closer-in to zero and this is one change
    I think helped my stability, some. But my understanding of
    this all is "shade tree" at best. Still, D param is what will
    best kill oscillation if it's control loop characteristics that
    you need to mess with (the problem is compound, the
    "plant" (motor) and the feedback loop).

  4. #4
    One of the things I messed with was getting it to idle stable and at one point had those under/over tables much smaller in value. It oscillated pretty bad at idle. I've leaned it out and upped the under/over values and played with the airflow. It seemed to get it stable in park/drive idle just sitting there. But once I apply throttle it either oscillates in gear driving down the road or hangs in park. So, I may have just band-aided it. I think I probably need to lean it out more in the lower RPMs. The wideband is no use there with the big overlap cam. It doesn't quite chop like it needs to, even at 900 RPM. So I'm guessing it's still running somewhat rich. Timing I may ramp up a bit. I think it'll take even more than 28 and be happy.

    I'll play with the A/F some more and log with the wideband and up the timing a bit. I'll see if that helps.

    Can you elaborate more on the P, I, and D parameters?

  5. #5
    Senior Tuner Russ K's Avatar
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    Jake, try out this tune. You delayed the EIOT by 62.91*, that is overkill as I believe that some of the fuel needs to hit the closed intake valve to help atomize it. So I delayed the EOIT by 25*. Also I'm not a fan of keeping the tune in open loop. I set up your closed loop tables to what works very well for my 418. In open loop, there is no good way to tune for a short heat soak condition like stuck in traffic with the a/c on or hot restarts. Also in open loop the evap purge is disabled, so the canister will become saturated with fuel vapor with no where to go (except into the atmosphere), and will cause an over loss of fuel mileage.

    Also I'm not liking that extra spark timing that was added to one of my spark tables. So I set it back to where I would put it. And 24* WOT spark timing is the MOST timing that any NA LS motor wants or needs (I'm at 22* with 11.5 cr 94 octane). And I've retuned several dyno tuned cars that had audible spark knock, as you can add some more timing on a dyno. But the car isn't WOT for very long on a dyno vs WOT for a quarter mile (or 1 mile) so there is a huge difference in combustion temps . They came to me with 28* WOT timing and had the knock tables desensitized. And you had your max retard in PE to 2*.

    But I had a 234/242 114 cam with 10* overlap that I got tired of the light throttle/low rpm surge. I have a M6 trans, so it was worse than an A4 with a loose convertor.
    So I replaced it with a 234/242/117+2 cam (4* overlap). The car drives 10x now, the idle is now 40 kpa vs 50 kpa. No more hunting/surging plus the car still has stupid bottom end power yet has more mid range to top end power due to the early EVO. I like driving my car again.

    So do a cold start idle scan and save it. Then do another warmed up and driving around with coasting to a stop.

    Russ Kemp
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  6. #6
    Thanks, Russ! I'll give it a try and will log it.

    And that's interesting on the camshaft. I would think 10 degrees would be okay in a 418. As you can see, the MAP readings for mine are around 70. Even at 900 RPM. At 1050+ they are 65. I'd love to have 65 kPa at 850. One thing it doesn't do now that it should is really lope. I figure it may need to be leaned out some more. I may take 5% out of the 400-1200 cells in the VE table and see what happens.

    Also, one other question. In CLSD, I won't have to worry about IAT heatsoak, but now I need to worry about going rich at idle due to the overlap of the cam. Is that what your revised setting "tune out" for the O2s?
    Last edited by JakeFusion; 10-17-2014 at 11:33 PM.

  7. #7
    Senior Tuner edcmat-l1's Avatar
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    That cam has a fair amount of overlap. There's a few things you need to do to keep it from oscillating when returning to idle.

    Open loop idle, and run it really lean.

    You'll want less timing when rolling. Try something around 22 degrees.

    You have too much rolling idle airflow. Even with big ass cams, and light flywheels, the MOST I usually need to use (rolling idle airflow adder) is about .5 g/sec in the higher MPH, and then tapering down to less than .1 g/sec @ 3 mph.

    The big key is leaning it out at idle though. Once you get it lean enough @ idle, you'll need to change a bunch of other stuff because it'll most likely idle too high (cruise control).

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  8. #8
    Thanks, Ed. Is there a way to enable Closed Loop for cruise? I'm thinking Open Loop is the only thing that will work at idle.

    And would you suggest I lean out the idle with the VCM bi-direction controller to determine what the equivalence ratio value is and then apply to my VE table in the 400-1200 RPM range? I plan to take it out tomorrow with the wideband and do more datalogging for the VE table but I want to lean it out in the idle. I guess I'll know when I hit the right ratio because it'll chop and stumble when it reaches the optimum lean condition? I'll disable adaptive spark too and make sure the timing is correct for that lean condition by watching the MAP kPa.

  9. #9
    Senior Tuner edcmat-l1's Avatar
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    You can set it up to be in open loop @ idle, and closed loop from 1200 rpm up.

    You can use your scanner bi-di controls to try and target your A/F, but I usually just chop away at it and watch my narrow bands.

    EFI specialist
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  10. #10
    Okay. Can you point me to the table in HPT? The Closed Loop enable table is all that I see and that's enabled via IAT in my version of the OS for 1-Bar SD for an 02. I'd love to be able to set the closed loop for 1200+.

  11. #11
    Senior Tuner edcmat-l1's Avatar
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    Do a search on here for open loop idle. It's not a single table.

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  12. #12
    Will do.

    Turns out I had most of this done, so I'll just doublecheck it. Also reset the temps for the IAT closed loop enabled back to stock.

    1. set PE to 1.0 up till 1200RPM
    2. set TPS enable PE to 0 up till 1200RPM
    3. set open loop F/A to 1.0 up till idle MAP, so if idle at 60kPa, 0-60kPa from say, 20*C up
    4. disable LTFTs (it sucks... a lot) (not necessary for this, but LTFT truly do suck)
    5. set PE MAP enable to 15kpa
    6. set PE enable delay RPM to 0
    7. disable the P0131 and P0151 DTC codes
    8. disable STFT open loop enable (if its not already)

    After I do VE tuning tomorrow, I'll re-enable DFCO as well.

    Russ, I kept all of your changes for the O2s and closed loop and your timing tables.

    Ed, I also adjusted the rolling idle airflow table. And the cracker/follower tables. And the VE. I noticed I had a pretty wide swing from 800 to 1200 RPM in the 65-75 kPa range. I'm sure that doesn't help with any surge.
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    Last edited by JakeFusion; 10-19-2014 at 12:25 PM.

  13. #13
    So, I messed with my VE table to get idle to settle in. I had to reallllllllllly lean it out before it would idle with adaptive idle OFF. I figured, great! It's chopping like it's supposed to and holding idle at 900 RPM without adaptive spark!

    But when I tried to rev it, nothing happened. Absolutely nothing. It actually dropped the RPMs. I had leaned out the VE table so much, there was almost no fuel available. Here are the two maps. First is "good idle" which makes the car undrivable. And the second is "decent idle" that has the car hunting for idle while driving around but I have throttle response. What should I do?

    Good Idle VE Map.png

    Decent Idle VE Map.png

    Edit: Nevermind. Did some logging and the 800 RPM column is where most of the fueling occurs at idle. I changed it and 400 RPM and kept 1200 the same. Idles fine... still not quite stable without the spark control, but it idles and recovers after a rev. The next test is driving around under load...
    Last edited by JakeFusion; 10-21-2014 at 03:09 PM.

  14. #14
    Senior Tuner Russ K's Avatar
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    Even a 100% stock engine hunts at idle with the adaptive spark disabled. I see that you put your EOIT back to 363.5, I would return to to the way I set it for you.

    Russ Kemp

  15. #15
    Okay. I used the spreadsheet soundengineer created based on cam timing events. I can back it off a bit.

    Here is the video of the idle and rev. And the log and tune. In park at least, it's still sluggish to rev. I'll take her out on the street tomorrow. Ran out of time after the issue with the idle lean out.

    http://youtu.be/wlDnVmPkGBY
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    Last edited by JakeFusion; 10-22-2014 at 12:44 AM.

  16. #16
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    JakeFusion, did you ever get your stalling dialed in? I see you said its close but still has a dip but have you ever been able to stop it from dipping?