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Thread: Still get oscillation coming to a stop

  1. #1

    Still get oscillation coming to a stop

    So I have battled this issue for 2 years with 2 different cams. Please help.

    When I come to a stop, the RPMs dip and usually oscillates pretty bad, but once I come to a complete stop, adaptive spark takes over, and everything is fine. It idles well. But I wouldn't say the idle is so stable that as a load is placed on the engine it will take it with ease (this is in SD or MAF/VE Blended - MAF only is rock stable, so I know there's an issue with the VE table).

    How did I tune idle? Turned adaptive spark off, set my timing at 20 degrees, and played with VCM Bidirection controls until it more or less idled on it's own (which pegs the wideband and the narrowbands end up reading like 20-30mv). It idles well at 850 with a 60kPa or so. But that's very lean. Cam has 5.5 degrees of overlap. It does not need to idle so lean. So when I turn on CL, the car adds fuel and it becomes unstable. Running with the MAF, I don't get that problem. I can run lean or rich in CL or OL and it idles fine. But as soon as I blend the VE table back in, the issues come back. But SD-OL is fine. Anything else with the VE table is flaky garbage. I have driven at low speeds and added 2% in the 400-800 columns until it becomes unstable while also taking 2% out. If I add 2-4% it goes unstable, but I can take 6-8% out and it doesn't seem to make a whole lot of difference (mainly cuz it's already pegging the wideband). I don't mess with the 1200 column a lot because it cruises there under 50mph. But there's a big delta between 800 and 1200 and that may not be helping in the VE table.

    Injectors are from the L9H 6.2L Flex Fuel. Data was converted from Gen IV PCM to Gen III. The injectors are not flow-matched and you can tell in the log. It idles lean no problem. So it's not a PW issue. Also, I've changed the EOIC and PW data in the fueling tab. Both consistent with how I did it with the bigger cam (used the same injectors there).

    As far as airflow, I actually plotted MAF air against IAC counts and Idle Desired Air (base airflow) against IAC counts as well. I've also plotted MAF Air and Dynamic Air (and they are typically within .5g of each other - so the VE table is close to the MAF transfer function or is that because it's running blended and using each other?). I've also logged Idle Desired against IAC counts and adjusted to where it's within .1g of reality. So the IAC Effective Area seems to be in line (also 22 steps ~ 1g sec airflow using the MAF as a check). I did drill a 3/16" hole in my 102 TB but have closed the blade enough to where the IAC steps are correct (or at least I believe them to be right enough).

    So I've been trying to play with Cracker on coastdown and it helps pad the air a bit. But the issue is when I log Dynamic or MAF air against Desired Airflow... it's off by 4g/sec. And worse yet, when I run the RussK idle configure it wants 4g/sec at temp. But the car will not run with that. It likes 7.4g/sec like what I have in there. Why such a huge discrepancy? I didn't have that with my other cam. Usually, I just put what was in the config and added .5g and it was dialed in. So there is something else going on with that too, and I feel like it's contributing to my issues.

    I've upped cracker enable/disable to 10/9 and that helps. But I feel like that's masking an issue. When I go back to stock 2/1 it really has problems.

    I'm running 2.2.4 on my tuning laptop, but have 3.4 on my Macbook and Windows 10. But I haven't tried to tune with it yet. So, I've attached my 2.2.4 tune. I have one log attached. I need to get a log in a parking lot with the oscillation, but I'd rather it work without adaptive nannies and then I can enable to really make it rock solid.

    I guess I could turn off the O2 sensor low voltage DTCs and go OL at idle... like I did with the bigger cam by setting PE to 1 in the idle cells. But I shouldn't have to.

    Any ideas?

    Specs:

    BTR 227/244 115+5 Cam
    TEA Stage 2 LS6 Heads (11.2:1 CR)
    FAST 102 and NW 102 TB
    TSP 100mm MAF with Screen
    Kooks 1-7/8" LT Headers and True Duals
    CircleD 4000 Stall
    3.23 Gears
    Attached Files Attached Files
    Last edited by JakeFusion; 11-26-2016 at 05:36 PM.

  2. #2
    In the log, you'll notice every time I come to a stop... I overshoot the idle (850) and end up in the 700s and then it surges back to 1300 to catch it. This is very annoying and noticeable when coming to a stop. Panic stops worry me because they could pull the car all the way down to a stall.

    The 9.5" stall isn't helping that but what can I do to clean up my return to idle?

  3. #3
    Senior Tuner Ben Charles's Avatar
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    I didn't get a chance to read everything... do this... gonink the scanner and command 16.0 when coming to a stop and see if it changes

    Email Tunes, [email protected]
    96 TA Blown/Stroked, 4L80E/Fab 9
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  4. #4
    I'll try that. I've commanded 16.1 at idle or for a slow roll. But I'm thinking of doing a parking lot tomorrow and setting lean and just rolling around under 30mph and try to stop and stop and turn. And see if it does ok.

  5. #5
    Senior Tuner Ben Charles's Avatar
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    Do both and report back

    Email Tunes, [email protected]
    96 TA Blown/Stroked, 4L80E/Fab 9
    15 C7 A8 H/C 2.3 Blower/PI
    14 Gen 5 Viper
    Custom Mid Engine chassis, AKA GalBen C

  6. #6
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    Tuning in, I've had surge I haven't been able to get under control for a while as well. Like you say, hit brakes hard and adapt idle grab it and idles fine. Rolling into a stop, never know exactly how it's going to behave. Annoying.
    70 Chevelle, 4L80e, 2900 stall, 02 LQ4 short block, LS3 heads/intake/injectors, Patriot extreme springs, EPS 222/230 on 112, Edelbrock 90mm TB, 85mm maf, Walbro 255