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Thread: Troubleshooting Help

  1. #1
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    Troubleshooting Help

    I'm looking for some help troubleshooting the following issues on my truck. Specs: 2012 silverado, z71. Mods are LS3 engine, Speed Engineering true dual exhaust with long tube headers. I've had the truck professionally tuned. It seems to run fine during acceleration. Makes good power. The problems are:
    1. Popping in the exhaust when letting off the gas. Maybe DFCO?
    2. Surging / Bucking when downshifting
    3. Rough Idle at stock idle levels. Tuner raised idle rpms which makes the truck idle smoother, but sucks for stop and go driving as it just wants to go.
    4. Poor idle regulation (idle speed overhoots / undershoots) mostly in in gear, rolling. RPM fluctuates 500 rpms peak to peak.
    5. Hiccups when crusing at partial throttle (especially when going up hill). Feels like a split second loss off power. Frequency varies, maybe 1/sec to 1/5sec
    5. Random Misfire code occurs at idle and only after some time since last reflash. Also error messages on dash for stabilitrack (sp?) and traction control. It's like the truck learns something after some driving, but whatever it learns is wrong.

    I don't know how to translate my problems into which procedures I should follow or how figure out which tables and settings can cause these issues.

    Tune ( https://www.dropbox.com/s/h7oc31xkfq..._dfco.hpt?dl=0 )

    Log ( https://www.dropbox.com/s/vf2qxwy6oq..._dfco.hpl?dl=0 )
    Last edited by jnnewton; 06-30-2019 at 01:30 PM.

  2. #2
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    Update: I installed a different type of spark plug yesterday. Went from an AC Delco conventional to an NGK V-Power. This has eliminated 1,2,5a. So I'm left with:

    3. Rough Idle at stock idle levels. Bit of popping in the exhaust at startup this morning.
    4. Poor idle regulation
    5. Random Misfire codes.

    I drove it 3-4 times until the misfire code yesterday. Then I started it up and got the misfire blinking CEL, traction control and stabilitrack errors. All but the CEL went away after about 1 minute. CEL stopped blinking and went off after about 10 minutes of driving. That was last night. Started it this morning and it struggled a bit (even though it is nice and warm out), but started and eventually evened out after about 10 minutes. No codes this morning.

    I ordered a set of taylor cable spark plug wires, recommended by my tuner. Will see how that goes when they show up and get installed next weekend.

  3. #3
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    Might want to take a look at your idle adaptive spark controls, with the idle bumped up to around 800 it's giving and taking 10deg or more at idle so yeah I bet it is rough... Grab a stock tune file and compare the adaptives. A new set of plug wires are always nice and never a bad idea, but not gonna fix what you got goin on at idle.

    Interpolate the idle adaptive values from the 0 to 128 rpm cells then back the idle down in increments. See if that helps.

    Worst case throw a stock tune on it and run 93 in it.

    If the truck's a daily driver, I'd cut traction control back on. Not a whole lot to gain by cutting it off, but plenty to lose. I've ran it both ways and there's more to gain on your tune (a lot more) by changing the torque management around a bit

    Nice truck you got goin, bet it sounds right running that dual setup!

    PM me if you got any questions on the idle stuff.

    Here's a good thread on dialing in gen IV idle https://forum.hptuners.com/showthrea...=sierra+denali

    Same process should work on your gen V.

    Good luck!
    Last edited by bzpharmer; 07-04-2019 at 01:00 PM.

  4. #4
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    I moved some of the adaptive idle stuff to or toward stock and was able to lower my idle and smooth it out a bit, but it still has a bit of a shake to it. My next round will attempt to back off the idle over/underspeed values to kill the oscillating idle speed i'm getting when in gear.


    The truck is a daily driver. As far as I know, traction control is on (I can toggle it with the button on my dash). The Speed Engineering exhaust sounds pretty rowdy at 3k+, but drones in the 1500-2000 range. I will be trying a different muffler in the near future (a magnaflow selected by the local exhaust shop based on my complaints and current setup.

    Any idea why the computer picked up 8 misfires while driving? I don't remeber feeling anything severe, and it looks like it picked up all 8 right in a row.
    Attached Files Attached Files
    Last edited by jnnewton; 07-07-2019 at 01:09 AM.

  5. #5
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    Meant to get back to ya way sooner on this man. Idle's looking better...

    I'm not gonna say those 8 misfires didn't happen, but I'm calling bs.

    Couple things:
    - Have you adjusted for tire size and gear?

    - Checked for exhaust/intake leaks? Double check. Triple check.
    - LS3 car intake manifold or truck style? Throttle body?

    Aight, enough questions lol.

    I've got a couple ideas of what's going on, but gotta get a good log with the right scanner setup otherwise I just got ideas.


    Shoot me a PM and I'll help ya out on the scanner layout that should be able to help ya get it figured out. 10-4 on the magnaflow, 22"canister on mine sounds GOOD.