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Thread: ls3 startup stumble

  1. #1
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    ls3 startup stumble

    I am working on a m6 ls3 camaro. it has 233/247 cam, full exhaust, cai, minor cylinder head work. basically when its hot and you try and start it fires then stumbles for a sec then it flares and runs perfect. i have tried adjusting cranking ve, cranking fa multiplier, startup air, cranking timing, i tried reducing the idle under and overspeed to 2 to see if that helped, reduced startup flare control to zero and everywhere in between. nothing seems to get rid of this and it doesn't do it when wold only when engine is warm. if you watch the log you can see that the timing is around 12 then it fires and goes to 0 (this is when it stumbles) then flares up but i cant seem to figure out where the engine is getting that number as the flare control and cranking spark tables only go to 800 and if you subtract the flare control from idle spark and low/high octane at that point the numbers dont match. I believe the base running airflow to be correct becuase if i turn the idle spark off (on) in scanner it idles right where its supposed to. thanks for any help in advance.
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  2. #2
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    I have witnessed the same thing on a 5th gen Camaro. I haven't messed with one myself. But I'd be very interested myself as to what is causing that. Hopefully someone will chime in.

  3. #3
    Senior Tuner 10_SS's Avatar
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    mine started doing this after I installed a whipple and a 2bar OS.. the Whipple came with injectors. Sounds similar however mine was worse right around 60-85F coolant temps.. Never figured out what caused the problem, however I can tell you if it cranks and fires normally then it's not your Cranking fuel.. I also played with all of the startup fare control, airflow, etc and nothing improved it.. just made it worse.. I finally decided it was lean in this area and increased the "Open Loop - IVT Gain" area in my temp.. .increased it 25%.. .now it fixed this problem completely..

    With your setup, your low RPM area shows -5 deg of advance the entire time cranking and first 1-2 sec of low RPM, then when RPM's start to increase so does advance... basically looks like your RPM comes up because timing comes up from -5 to 6-12 deg. You may want to play with that first. Mine cranks and starts with 5-10deg advance depending how hot it is. 3-13 in this window when coolant is 185. I have a blip on my startup that timing drops to 0 for one frame and looks like RPM kinda hangs for that frame too.
    2010 Camaro LS3 (E38 ECU - Spark only). MS3X running complete RTT fuel control (wideband).
    Whipple 2.9L, 3.875" Pulley, kit injectors, supplied MSD Boost-A-Pump, stock pump
    LG Motorsports 1 7/8" Headers - No Cats, stock mid pipe with JBA Axle Back
    ZL1 Wheels/Tires

  4. #4
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    where are you referencing the -5 from the frare control table. cranking spark is at 12 when warm. i was under the impression that the flare control table reduced timing which was referenced from another table.

  5. #5
    Senior Tuner 10_SS's Avatar
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    Crank spark looks fine, at 12 deg. I don't know where the running spark is coming from... I just noticed in the log it's -5 as RPM continues to come down until it starts to increase... then your RPM's start climbing.
    2010 Camaro LS3 (E38 ECU - Spark only). MS3X running complete RTT fuel control (wideband).
    Whipple 2.9L, 3.875" Pulley, kit injectors, supplied MSD Boost-A-Pump, stock pump
    LG Motorsports 1 7/8" Headers - No Cats, stock mid pipe with JBA Axle Back
    ZL1 Wheels/Tires

  6. #6
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    I've noticed this as well. Cranking and idle spark at 13-15* seem to help a tad, but i'm still curious to what people find.

  7. #7
    Senior Tuner 10_SS's Avatar
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    151 views... not many comments. The other tables I played with with no success were the Idle/Airflow/Startup tables.. there's a Startup Airflow table in there that I played with... but anything I did there had no effect, actually made it worse.. not better, that's because I was lean... not low on air. Though you may need more air since you have a cam. The thing that fixed mine was adding ~15% more fuel to the Fuel/Open+Closed Loop/IVT Gas Gain tables around 61-90F IVT, 25-65kpa MAP.. it actually probably was too much fuel now but RPM is rock solid.. I get just a little bit of lope now where it used to stumble which is typical for rich fuel condition.. it goes away after just 3-4 seconds so I'm ok with it.. now I should reduce fuel by 2-3% until it's perfectly clean.

    So if I were you I would add some airflow (10-20%) to the Startup Airflow table around the engine run time and temp that you have the problem, if that does nothing... add more. If still nothing then put back to stock and add 15-20% to the fuel table I mentioned above... by adding so much it makes it very noticable change... much better than adding 2-5% for a first shot in the dark.
    Last edited by 10_SS; 09-11-2015 at 04:11 PM.
    2010 Camaro LS3 (E38 ECU - Spark only). MS3X running complete RTT fuel control (wideband).
    Whipple 2.9L, 3.875" Pulley, kit injectors, supplied MSD Boost-A-Pump, stock pump
    LG Motorsports 1 7/8" Headers - No Cats, stock mid pipe with JBA Axle Back
    ZL1 Wheels/Tires

  8. #8
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    What injectors?
    Post a log and tune if you want help

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  9. #9
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    Start up airflow looks really low. I am currently tuning a 2012 heads/cam l99 Camaro and had to almost triple the start up airflow tables. Try adding 50% to the table and see if it gets any better. Where you see 87.3, mine is 150.9...
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