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Thread: "Breaking up" when in boost?

  1. #1
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    Default "Breaking up" when in boost?

    Engine is running nice and smooth idling or cruising, but when I get into boost it wants to break up badly. No misfires logged. Taking a look at this log I think this corresponds to intermittent AFR dips into the 9's on WO2AFR1 which I think is actually on bank 2. Not that I trust the accuracy of the dual LC1s, but it looks like there is a correlation here. A free air cal was done immediately prior to this log.

    Motor has fresh coils, wires, plugs which definitely improved how it runs otherwise, but didn't help with this issue. Injectors are also new this year - ID1000 high Z. Current plugs are 8's gapped at .025. Any ideas? Take a look the spots where I give it some throttle and check out the WO2 traces. Didn't have this issue last year before the rebuild.
    Attached Files Attached Files
    2017 Camaro SS, 2014 Ram 2500 4x4 Cummins 6.7L, 2004 Chevy Avalanche Z71 4̶X̶4̶(now 2WD), 5870lb race weight, 10.93@ 124, Twin TVS1900s, Twin Throttle, 429 LSX, 4L80E, custom 14 bolt rear, V2, R̶o̶a̶d̶R̶u̶n̶n̶e̶r̶(dead), COS3......
    Gettin' the Groceries

  2. #2
    Joe (Moderator) joecar's Avatar
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    Hi DrX,

    Not only does measured AFR dip excessively rich, but ignition timing pretty much goes to zero.

    I can tell by DYNCYLAIR that the VE table is off, I think this is the problem, correcting the VE will get the AFR correct and ignition timing correct.

    Can you log SPARKADV...?

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    I will get that(base spark) next log - deleted it to make room for state00. It was basically identical to run spark except in boost where I am pulling around 4* with A0010. Started tuning with VE scaled 50% and spark tables shifted accordingly from where I was last year. Didn't need scaling last year due to higher FP in boost with the dual FPR fuel system I was running. If VE is off now, one or both widebands are screwed up. To make it even more intersting, in today's log that wide band was dropping to 9 intermittently just cruising!
    Attached Files Attached Files
    2017 Camaro SS, 2014 Ram 2500 4x4 Cummins 6.7L, 2004 Chevy Avalanche Z71 4̶X̶4̶(now 2WD), 5870lb race weight, 10.93@ 124, Twin TVS1900s, Twin Throttle, 429 LSX, 4L80E, custom 14 bolt rear, V2, R̶o̶a̶d̶R̶u̶n̶n̶e̶r̶(dead), COS3......
    Gettin' the Groceries

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    Here is a new log with A0010 zeroed out. Still get the "popping" from the exhaust in boost (actually sounds more like rapid fire shotgun blasts).
    Attached Files Attached Files
    2017 Camaro SS, 2014 Ram 2500 4x4 Cummins 6.7L, 2004 Chevy Avalanche Z71 4̶X̶4̶(now 2WD), 5870lb race weight, 10.93@ 124, Twin TVS1900s, Twin Throttle, 429 LSX, 4L80E, custom 14 bolt rear, V2, R̶o̶a̶d̶R̶u̶n̶n̶e̶r̶(dead), COS3......
    Gettin' the Groceries

  5. #5
    Joe (Moderator) joecar's Avatar
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    Spark timing is being pulled down alot during boost... do any of the EST_xxxx_DMA pids show the reason...?

  6. #6
    Lifetime Member swingtan's Avatar
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    Any chance you have a loose plug lead? looks like the rich spikes occur even when cruising.

    Simon.

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    Were the spark plug wires melted? It seems to be a re-occurring issue with mine.
    E85 is NOT flex fuel.

    2003 Chevy S10 4.3L LU3 LS1B Auto
    48 LB injectors
    Race Proven Motors 2114 intake
    T70 turbo.

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    The timing appears to be exactly what is being commanded by the High Octane table.

    I replaced the plug wires without any improvement. No misfires logged even though it is obvious.
    Attached Files Attached Files
    2017 Camaro SS, 2014 Ram 2500 4x4 Cummins 6.7L, 2004 Chevy Avalanche Z71 4̶X̶4̶(now 2WD), 5870lb race weight, 10.93@ 124, Twin TVS1900s, Twin Throttle, 429 LSX, 4L80E, custom 14 bolt rear, V2, R̶o̶a̶d̶R̶u̶n̶n̶e̶r̶(dead), COS3......
    Gettin' the Groceries

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    Looking at the rich spikes logged on WB1 which occur both cruising(more so at MAP values below 60 kPa) and always when into boost(multiple spikes at short intervals- .1 -.3 sec), what could cause this?

    1. A bad wideband
    2. A sticky injector
    3. Intermittent loss of spark on 1 or more cylinders
    Any others?

    Now which is most likely and why would it get worse in boost?

    Injectors, plugs, coils, wires are new. Plugs are gapped at .025"
    2017 Camaro SS, 2014 Ram 2500 4x4 Cummins 6.7L, 2004 Chevy Avalanche Z71 4̶X̶4̶(now 2WD), 5870lb race weight, 10.93@ 124, Twin TVS1900s, Twin Throttle, 429 LSX, 4L80E, custom 14 bolt rear, V2, R̶o̶a̶d̶R̶u̶n̶n̶e̶r̶(dead), COS3......
    Gettin' the Groceries

  10. #10
    Lifetime Member swingtan's Avatar
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    The sound described sounds very much like a misfire. If it's accompanied by a distinct lack of power, then I'd say it's dropping one or more cylinders. You may not get a misfire DTC though....

    My thinking is that the ECM needs to know what a misfire is before it can detect one. In stock form, this is done on the stock tune with a CASE learn, the basics of which are that the ECM causes a deliberate misfire so it knows what it looks like on the crank angle sensor. If you go and change the motor and tune a lot, then the learnt misfire data is no longer valid. Unless a CASE relearn is performed, you may not detect a misfire. This is all theory by the way, I haven't really tested it.

    I'd recheck the leads and plugs. You may need to perform and old time "plug reading" by pushing the motor to the point that sustained misses occur and then shuting off the motor straight away. Then pull the plugs to look for obvious differences.

    I'd also do a "black" test on the leads. Run the car in the dark and look at the engine bay. In the dark, you'll be more likely to see any ignition spark leaks from the wires and coils.

    0.025" may be a little narrow on the plug gaps and not allowing sufficient mixture between the electrodes to fire the mixture. Going along with this is the "8" reference for the plugs. Is that the heat range for them? If so, that's a pretty cold plug and may be causing issues. Most people I know that are running boost run a "6", or at the most a "7". You may be fouling the plugs as they are too cold to keep clean. A read of the plugs should tell the story, but I'd try a "6" heat range plug gapped at 0.035"

    Simon.

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