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Thread: Exhaust pops under acceleration.

  1. #1

    Default Exhaust pops under acceleration.

    LS3, HP EFI, no issues until new header back exhaust. Old system was Magnaflow with H-pipe. New system, Borla no H-pipe. Both 2.5". Now under hard acceleration in 2nd gear I hear some pretty consistent exhaust pops on just the passenger side exhaust. Looking at the AFR it seems to be more rich than lean.
    Settings:
    Idle: 14.0
    Cruise: 13.5
    WOT: 12.5
    Any ideas?

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,973

    Default

    I went through a slight retuning process many years ago, when I custom built my dual 3" exhaust system with Magnaflow mufflers (LINK) for my Bronco. Simply put, if the engine makes more power, it'll need more fuel (Base Fuel Table, not necessarily Target A/F Ratio table). Pay special attention to the center paragraph in blue print:

    Originally Posted by Danny Cabral
    Quick Datalogger Information:
    Always provide data, not just symptoms. Is the AFR & ignition timing optimized? Overlay the datalog onto your Global File.
    Ensure the Target A/F Ratio table is properly programmed for your engine. Ensure the ECU is "Learning" (Learn Table LINK).
    Scroll through the datalog to the problem area. Then look exactly where this happens on the Base Fuel & Timing Tables. Scrutinize:
    RPM, MAP, MAT, TPS, CTS, IAC, Target AFR, AFR Left, CL Comp, Ignition Timing, Duty Cycle, Fuel Flow, Fuel Pressure & Battery.

    Using the Holley EFI software (LINK), look at where the live cursor moves to during this occurrence, and
    manually tune that area of the Base Fuel Table (enrich or lean) & Base Timing Table (optimize ignition timing).


    I find the most helpful datalog function, is overlaying the datalog on your Global File.
    I'm in the habit of using the datalog Overlay feature every time I review a datalog.
    Click on "Datalog" (on the top Toolbar), "Activate Overlay", then "Open Data Log".
    You can literally "playback" a recorded event, and watch it as it happened on any screen.
    Minimize (shrink) the datalog window, and move it to the bottom of any Global File screen.
    Then click & scroll anywhere on the datalog, and watch it playback on your Global File (EFI software).
    http://documents.holley.com/techlibr...9r10543rev.pdf (Holley EFI Datalogger Instructions)
    https://forums.holley.com/showthread...s-amp-Datalogs (Datalog & System Log Information - Read "NOTES")
    https://www.youtube.com/watch?v=iqHO...C6FEA0BB99AF17 (How To Record & Email A Datalog)
    https://www.youtube.com/watch?v=q7OZUXLRS1Q (How To Record A System Log & Diagnose A No-Start Condition)
    https://forums.holley.com/showthread...7531#post77531 (Closed Loop Datalog Tuning - Posts #2, #4 & #6)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #3
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
    Posts
    1,580

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    Quote Originally Posted by another69 View Post
    Old system was Magnaflow with H-pipe. New system, Borla no H-pipe. Both 2.5".
    Why run a dual exhaust without a crossover? Even an H-pipe crossover it better than nothing, albeit old school. An X-pipe crossover is the go. Gary
    Regards, Gary

  4. #4

    Default

    Thanks for the link & info Danny. I thought about doing a datalog, but I'm not sure how it would see the "pops". The car doesn't seem to lose any power or stumble, just some exhaust noise. Only seems to be hard acceleration 2nd gear. I'm trying to keep an eye on the AFR when it does it, and it seems to be rich, like 11:1 or so while making the noise. What actually makes the noise? A lean condition, rich condition, or either? Could eliminating the H-pipe make that much of a difference? Or Borlas flow that much differently than Magnaflow? I only got rid of the H-pipe due to the new torque arm suspension. Not much room for one, unless it's a smaller diameter.

  5. #5
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
    1,431

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    Are you using ACDelco plugs? I had a problem with them being dead right out of the box. They were giving me a popping in the exhaust under hard acceleration. Did you measure the resistance of each plug & wire?

  6. #6
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,973

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    Good point. I only use NGK Iridium IX spark plugs.
    https://forums.holley.com/showthread...4896#post54896 (Additional Spark Plug Information)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  7. #7

    Default

    The LS3 I have has about 3000 miles on it (crate engine), but I went ahead and checked the plugs & wires on the right bank (where the problem occurs):
    Plugs:
    #2= 4.26K
    #4= 4.69K
    #6= 5.35K
    #8= 5.03K
    Wires:
    #2= .802K
    #4= .774K
    #6= .759K
    #8= .789K
    Not sure where they should be, but they appear somewhat consistent. Stock ACDelco plugs & wires.

  8. #8

    Default

    If it's not ignition related, could it be timing related or an AFR mixture issue? It doesn't seem to lose any power.

  9. #9

    Default

    Did a datalog today, and nothing really stands out, except maybe the ignition timing which may not be right on for an LS3. Both banks have very similar AFR readings, low 12s when the exhaust is backfiring under load. Only on the passenger side. Can an exhaust change really do this?

  10. #10
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,973

    Default

    Quote Originally Posted by another69 View Post
    Can an exhaust change really do this?
    Yeah, maybe it's something else.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

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