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Thread: Misfire issue on stock 4.8 with external FP setup.

  1. 01-23-2017 #21
    GN_Drake
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    Well, had the engine picked up and taken to Triple Edge Performance today. Going to have them look it over, install my Triple 12, studs, melling 10295, and all new gaskets. Then freight it to me with my 4L80e and Precision TC. Anything I am missing? Trunion setup?

    For now I wait... And I am going to try a new crank sensor on the 4.8 to see if that helps. Time is hard to come by, so hoping to have that done by the weekend.

    Also chasing some current draw from an unknown source. Radio fuse is already pulled, but I am going to hookup the DMM to the battery and start pulling fuses until I can find the source. Then I will try to rectify that issue as well. Seems like im always moving backwards, never in the right direction

    DW also called me back today about my suspect DW350iL issue I had. They are going to warranty out the pump and send me a brand new one. Even though I already bought one local, I will either keep this for future use, or sell it for some other random parts.

    Staying the course, wasting the money, enjoying the hate.
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  2. 01-24-2017 #22
    steve smith
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    pay close attention to wires connecting to fuse box.. wire gauge was to small from factory causes all sorts of crazy problems..
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  3. 01-24-2017 #23
    GN_Drake
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    Exactly which wires are you referring to? I have never heard of any wires going into fuse box as being too small. I have spent many hours reading up on issues, but never heard that one.
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  4. 01-29-2017 #24
    GN_Drake
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    And the plot thickens...

    Was out scanning and messing with closed loop/trims. I wanted to leave the truck running long enough to hit 200* to make sure my e-fans would turn on like they should (never verified after adding them and tuning). All worked as planned.

    Put the truck in gear and footbraked it to see if the missing remained, it did not. So I took it for a short drive, everything felt and acted normal without misfiring. Park it in driveway, and have misfires again. So it is only when the truck is in Park/Neutral that it is having bad misfires. Not really sure what this tells me, thoughts?

    Here is the log for your viewing pleasure. I am....perplexed03 Sierra 01292017 drive.hpl
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  5. 01-29-2017 #25
    Earwax
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    Is it actually missing that you feel or is it just showing missfires on the scanner?
    Did you do the crank relearn procedure?
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  6. 01-31-2017 #26
    GN_Drake
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    It actually misses that you can hear and feel. I have done crank relearn a couple times. Truck has oddly been running fine while in gear, just missing when if park. I may try another relearn on this PCM to see if it helps anything, but I am even more curious on what is happening now that is drives in gear.

    I was just unplugging sensors to check things over, added a zip tie to PCV, and did some foot brake tests, then it all the sudden started acting much better....
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  7. 01-31-2017 #27
    Earwax
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    Vacuum brakes? If so, try disconnecting and plugging the booster hose.Also try pumping the brake pedal while it misses and watch the fuel trims.I would also check any grounds and move the harness/connectors while its missing. Had a truck at work that ate 2 cats on the same side, I found a loose pin in the coil connector for the same bank.As said before you need to verify spark and inj pulse while it misses.Just a few ideas to try?
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  8. 01-31-2017 #28
    GN_Drake
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    I have changed out all coils, wires, and plugs. Added/checked the grounds. Now have an extra 4ga going to bottom of the block. None of this changed anything. Verified spark and spark command via probing the PCM with an O-scope. Same for injectors commands. I have an extra set of injectors I can install, just havent tried them yet while chasing other items.

    I will look at trims while on brakes, not sure it effects it at all since when it is in drive there are no misses... But something to look at nonetheless.
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  9. 02-02-2017 #29
    GHuggins
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    Only misfires hot without load is more than likely cylinder leakage or carbon. Use the scanner controls to increase the rpms while the problem is present to see what rpms it goes away at.
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  10. 02-03-2017 #30
    GN_Drake
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    Once the truck warms up, misfires now pretty much go away. If I try to drive it before it is warmed up, it has a similar misfire problem. Once warmed up, drive nearly perfectly.

    However, now it appears to be a lean condition like my FPR isnt doing its job. I do not have a FP gauge to watch while driving, so I am going to go out and watch while the wife revs the engine. See scan:
    03 Sierra 02032017 lean.hpl
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