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Thread: Diagnose hesitation/backfire under load & boost?

  1. #1
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    Diagnose hesitation/backfire under load & boost?

    Here's what I've got. 2010 Camaro SS 6 speed manual with a 419ci LS3 with twin turbo's generating a peak of 12psi boost. I recently upgraded to the HPT custom 3-bar OS and am in the process of tuning it. I've completed the idle and normal driving areas of the tune and began working on the boosted areas.

    The problem is that it backfires and hesitates bad when under loaded boost conditions. For example, if I take the RPM's down to 2500 in 4th gear and go to WOT the boost will reach 6-7psi at 3500-4000 and the engine begins to hesitate and backfire pretty violently.

    Looking at the log I've created, nothing is indicative of cause, timing isn't pulled and fuel delivery seems to be fine. The MAF log looks a little choppy, but it's always been that way.

    To rule out ignition issues, yesterday I swapped the coil packs and wires, and regapped the spark plugs to 0.030.

    Any ideas on how to diagnose this would be much appreciated!! Are there some PID's I can log that will help?

  2. #2
    Senior Tuner IDRIVEAG8GT's Avatar
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    Typical cause of that is going lean. Needs more transient fuel.

    Post your tune chief.
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    Lol. Post a log. No tune needed. What is the afr doing when the trouble starts. Dont think transients apply at wot 4000 rpm. He has been wot for almost 2000 rpm by time the problem starts. You probably have a combination of to rich afr and are blowing out the spark. The engine is heavily loaded doing a run like this versus just going through the gears at wot.
    98 s10 5.3 5spd.

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    Quote Originally Posted by IDRIVEAG8GT View Post
    Typical cause of that is going lean. Needs more transient fuel.

    Post your tune chief.
    I think you're on to something, if you look at the attached log at frame 7626 the commanded afr goes to 11.74 but the wideband says the afr remains 14.6x.

    Tune is attached too.
    Last edited by RookieTuner; 12-15-2012 at 08:11 PM.

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    Quote Originally Posted by 98S10 View Post
    Lol. Post a log. No tune needed. What is the afr doing when the trouble starts. Dont think transients apply at wot 4000 rpm. He has been wot for almost 2000 rpm by time the problem starts. You probably have a combination of to rich afr and are blowing out the spark. The engine is heavily loaded doing a run like this versus just going through the gears at wot.
    Trouble starts at frame 7662 and I got out of the throttle soon after.

  6. #6
    Senior Tuner IDRIVEAG8GT's Avatar
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    Quote Originally Posted by 98S10 View Post
    Lol. Post a log. No tune needed. What is the afr doing when the trouble starts. Dont think transients apply at wot 4000 rpm. He has been wot for almost 2000 rpm by time the problem starts. You probably have a combination of to rich afr and are blowing out the spark. The engine is heavily loaded doing a run like this versus just going through the gears at wot.
    You don't like me do you?


    Quote Originally Posted by RookieTuner View Post
    I think you're on to something, if you look at the attached log at frame 7626 the commanded afr goes to 11.74 but the wideband says the afr remains 14.6x.

    Tune is attached too.
    Will take a look when I get to my HPT laptop.
    Last edited by IDRIVEAG8GT; 12-16-2012 at 01:38 AM.
    Gray Ghost- The abomination. 2007 Chevrolet Silverado CCSB. 98mm turbo, nitrous, 428LSX, Rossler 80E with a brake. Finally finished. 23 psi, no numbers, Slow as hell.

    PBM G8- Aluminum 364, twin Precision 67/66 turbos, 6L90 trans swap, CTS-V/Vaporworx fuel system, slowly making progress.

    Dads 2011 CTS-V- Stock bottom end, stock heads, LS9 cam, pullies, ported blower, ported TB, D3 goodies, and lots of nitrous.
    618/618 motor
    906/862 spray

    Caterpillar 50 Forklift- Duramax swap

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    [QUOTE=IDRIVEAG8GT;312304]You don't like me do you?

    Lol. Thats not true. Guess Im a bit grumpy. Sometimes I think you inadvertently steer people in the wrong direction.
    98 s10 5.3 5spd.

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    Seems to me that if you were going that lean at that load and rpm, 7+ psi boost, That you would have bad detonation and would have hurt the engine.
    98 s10 5.3 5spd.

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    Quote Originally Posted by 98S10 View Post
    Seems to me that if you were going that lean at that load and rpm, 7+ psi boost, That you would have bad detonation and would have hurt the engine.
    There is no knock retard and I didn't hear any pinging. I'm not at WOT when this happens.

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    you are running hybrid sd/maf, you need to fail the maf, tune SD. then disable dynamic and tune the maf. cant tune with both enabled.

    -Carl

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    Quote Originally Posted by carlrx7 View Post
    you are running hybrid sd/maf, you need to fail the maf, tune SD. then disable dynamic and tune the maf. cant tune with both enabled.

    -Carl
    Yes, I understand and have done that, but the OS delays entry to PE for some reason (regardless of whether it's in MAF, SD, or hybrid). I think this is causing the lean condition and preventing tuning in higher regions of the MAF and VE table. I think there's a problem with this custom OS as I just switched back to the base E38 tune file and it's running fine.

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    change your Boost PE from 115 to your local baro, aka like 98.

    and post the tunes you think are correct for running pure maf and pure SD
    Last edited by carlrx7; 12-16-2012 at 02:04 PM.

  13. #13
    Senior Tuner DSteck's Avatar
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    See other thread.

    Make sure your fuel pressure will keep up.

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  14. #14
    Senior Tuner IDRIVEAG8GT's Avatar
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    Yeah there's some things I'd like to see changed in this tune that would help greatly. As Carl mentioned the car needs to properly put into SD and then there's several tweaks that need to be made to the PE (Enable Requirements) of the the tune to make it respond faster.

    Detonation isn't always present with severe lean spikes. Hot flashes are, but not detonation. Typically if one detonates from an over lean condition under boost, it'll knock the tip off a spark plug. In this case it looks like a dead spot to me.
    Gray Ghost- The abomination. 2007 Chevrolet Silverado CCSB. 98mm turbo, nitrous, 428LSX, Rossler 80E with a brake. Finally finished. 23 psi, no numbers, Slow as hell.

    PBM G8- Aluminum 364, twin Precision 67/66 turbos, 6L90 trans swap, CTS-V/Vaporworx fuel system, slowly making progress.

    Dads 2011 CTS-V- Stock bottom end, stock heads, LS9 cam, pullies, ported blower, ported TB, D3 goodies, and lots of nitrous.
    618/618 motor
    906/862 spray

    Caterpillar 50 Forklift- Duramax swap

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    Tuner in Training HSVTT's Avatar
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    I Had I very similar problem. IDRIVEAG8GT might remember it at first I though it was the intake, then I flashed in a new computer still nothing. It was very bad under load like yours and I have a very similar setup. In the end it was a bad earth on the back of the motor. This is hard to see when you install the new motor. When you are under load all the voltage is drained from the injectors and spark causing havoc. Balance test and DTC's showed nothing.There are two earth straps and both need to be good. here is a short vid of mine with half hour street tune. Soon going on dyno. http://youtu.be/HEi8rmQLPRQ .Worth a shot it took me about 40hours of pain to nail the problem. Im happy to send you my basic tune If you want a look.

  16. #16
    Senior Tuner IDRIVEAG8GT's Avatar
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    Quote Originally Posted by HSVTT View Post
    I Had I very similar problem. IDRIVEAG8GT might remember it at first I though it was the intake, then I flashed in a new computer still nothing. It was very bad under load like yours and I have a very similar setup. In the end it was a bad earth on the back of the motor. This is hard to see when you install the new motor. When you are under load all the voltage is drained from the injectors and spark causing havoc. Balance test and DTC's showed nothing.There are two earth straps and both need to be good. here is a short vid of mine with half hour street tune. Soon going on dyno. http://youtu.be/HEi8rmQLPRQ .Worth a shot it took me about 40hours of pain to nail the problem. Im happy to send you my basic tune If you want a look.
    Ahha earth straps. I actually like that better than saying ground strap. :O
    Gray Ghost- The abomination. 2007 Chevrolet Silverado CCSB. 98mm turbo, nitrous, 428LSX, Rossler 80E with a brake. Finally finished. 23 psi, no numbers, Slow as hell.

    PBM G8- Aluminum 364, twin Precision 67/66 turbos, 6L90 trans swap, CTS-V/Vaporworx fuel system, slowly making progress.

    Dads 2011 CTS-V- Stock bottom end, stock heads, LS9 cam, pullies, ported blower, ported TB, D3 goodies, and lots of nitrous.
    618/618 motor
    906/862 spray

    Caterpillar 50 Forklift- Duramax swap

  17. #17
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    Quote Originally Posted by HSVTT View Post
    I Had I very similar problem. IDRIVEAG8GT might remember it at first I though it was the intake, then I flashed in a new computer still nothing. It was very bad under load like yours and I have a very similar setup. In the end it was a bad earth on the back of the motor. This is hard to see when you install the new motor. When you are under load all the voltage is drained from the injectors and spark causing havoc. Balance test and DTC's showed nothing.There are two earth straps and both need to be good. here is a short vid of mine with half hour street tune. Soon going on dyno. http://youtu.be/HEi8rmQLPRQ .Worth a shot it took me about 40hours of pain to nail the problem. Im happy to send you my basic tune If you want a look.
    WOW, bet that was a bear to diagnose! I suppose monitoring for a drop in ignition voltage with HPT might give a hint to this problem.

  18. #18
    Tuner in Training HSVTT's Avatar
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    Yea have a look. If not I run a E38 aswell I will send you my tune to look at and try you will just have to change for your injectors I have the same size motor. Haha Earthstrap! Aussie talk lol.

  19. #19
    Senior Tuner IDRIVEAG8GT's Avatar
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    Yep I wish I could have been a better help diagnosing it. I've never ran into that issue before HSVTT.
    Gray Ghost- The abomination. 2007 Chevrolet Silverado CCSB. 98mm turbo, nitrous, 428LSX, Rossler 80E with a brake. Finally finished. 23 psi, no numbers, Slow as hell.

    PBM G8- Aluminum 364, twin Precision 67/66 turbos, 6L90 trans swap, CTS-V/Vaporworx fuel system, slowly making progress.

    Dads 2011 CTS-V- Stock bottom end, stock heads, LS9 cam, pullies, ported blower, ported TB, D3 goodies, and lots of nitrous.
    618/618 motor
    906/862 spray

    Caterpillar 50 Forklift- Duramax swap

  20. #20
    Senior Tuner IDRIVEAG8GT's Avatar
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    No I didn't have a problem. Do you have the .808 beta?
    Gray Ghost- The abomination. 2007 Chevrolet Silverado CCSB. 98mm turbo, nitrous, 428LSX, Rossler 80E with a brake. Finally finished. 23 psi, no numbers, Slow as hell.

    PBM G8- Aluminum 364, twin Precision 67/66 turbos, 6L90 trans swap, CTS-V/Vaporworx fuel system, slowly making progress.

    Dads 2011 CTS-V- Stock bottom end, stock heads, LS9 cam, pullies, ported blower, ported TB, D3 goodies, and lots of nitrous.
    618/618 motor
    906/862 spray

    Caterpillar 50 Forklift- Duramax swap