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Thread: Part Throttle Misfire Cammed LQ4

  1. #1
    Junior Member
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    Oct 2011
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    Default Part Throttle Misfire Cammed LQ4

    Takes a lot for me to get stumped but I'm getting there quickly on this one. Vehicle is an 07 Avalanche with an LQ4 swap, 227/234 111lsa camshaft, shorty headers, the rest is pretty much stock. Has GM Truck 36lb Flex Fuel injectors in it. The truck runs perfect, idles great but has a part throttle medium load pop through the exhaust that will not go away. Happens around 20% throttle area at 2500-3300rpm, start popping out the exhaust, give it more throttle goes away. The only way I've been able to get rid of it is to bring PE in WAY early like 12-14% throttle area, which in the past 10+ years of tuning vehicles I've never had to do. If its in closed loop and running 14.5~ AFR it will pop, if I fatten it up in PE or take it out of CL and command 13.5 or less the pop will clear up. Ive moved timing around in the area from 15 to 27* nothing changes it. Tried running SD with the VVE only, still does it. Tried running full MAF mode with the high speed air calc pid set to 1000rpm, still happens. Happens around 75-85kpa of MAP. Seemed mechanical to me so we swapped injectors, coil, plugs, wires, no change. Pulled the truck intake off to make sure no one rolled a gasket, re gasketed it no change. Did a compression test and leak down, all looks ok.

    As a test I temporarily turned misfire detection back on above 2000 rpm and the PCM did show misfire on cyl 3 when the issue is happening.

    The customer is insisting its the tune but I just don't see it but I'm not completely closing my mind to anything at this point.

    Would love if anyone has any input or any suggestions, I have the customers vehicle here now so I can go data log and post if need be.

    Tune file is attached.BLT_2109_1_0004.ctz

    Thanks in advance!

  2. #2
    Joe (Moderator) joecar's Avatar
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    Default

    Post log files.

  3. #3
    Joe (Moderator) joecar's Avatar
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    Is rail pressure within spec?
    If FPR is at rail (i.e. return system), is it leaking (ruptured)?

    Are spark plugs good and at correct gap?
    Are plug wires good/new?

  4. #4
    Senior Member
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    Jan 2010
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    Default

    You know, I recently had an issue with a LS1B where the file was some how corrupted. I used an updated OS setup for a 6.0L swap. Everything seemed normal but the thing would bog Under WOT and start leaning out. We made all sorts of changes and could not figure it out. Finally we tried a different file with a full flash and made the necessary changes and it worked. Not Sure how the other file was corrupted but that is all we can figure.

  5. #5
    Joe (Moderator) joecar's Avatar
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    Did a full flash fix it?

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