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Thread: Mystery misfire

  1. #1
    Member RuLEoF2's Avatar
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    Default Mystery misfire

    So, I'm persistently getting misfires on cylinder 6 which is #5 being 6th in the firing order. I've already ruled out the plug, plug wire and coil by way of swapping the coil and replacing all of the plugs and wires with brand new. I checked compression and compared with neighboring cylinders. 110 PSI on #1, 135 on #3 and 125 on #5. I've never done a compression check before so I asked an experienced DIY mechanic buddy and he said that those were good numbers. Finally, I bought a 2-pack of those plug testers and put one on #5 and #1.

    #1 has a strong and consistent pulse. #5 not so much. That one will occasionally only flicker or skip altogether. These occurrences seem completely random and sometimes come in tightly grouped waves of random combinations lasting about 5 seconds. Time between individual occurrences or waves is anywhere from 15 seconds to over a minute.

    I suppose the next target is the coil connector and it's wires. My DIY buddy has been doing research for me and found stuff about bad crank shaft sensors potentially being the cause. I'm running out of ideas so any thoughts or suggestions would be greatly appreciated.

    Thanks for reading.
    2009 G8 GT
    Passion Red
    Sport Package
    Vararam CAI
    Borla Exhaust

  2. #2
    Member RuLEoF2's Avatar
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    Default

    I've been busy trying to figure this out. Since I started this saga, I've learned that the P0306 reference to the sixth in the firing order is not correct as it was stated in the article where I read it and it is in fact referring to cylinder #6. I then switched back to focusing on #6 and still no luck to date.

    So, I figured that I should post a summary of all the troubleshooting I've done to bring it all together. This is what I've done so far.

    * Swapped coils between 4 and 6
    * Swapped coils between 3 and 5
    * New B2/S2 oxygen sensor
    * All new spark plugs
    * All new plug wires
    * Verified coil discharge with inline tools on #'s 1, 3, 4, 5 and 6
    * Checked cylinder compression on: #6 = 130 psi, #5 = 125 psi, #3 = 130 psi, #1 = 110 psi
    * Checked resistance on injector 6 = 12.7 ohms
    * Checked resistance on injector 5 = 12.8 ohms
    * Checked accessory power voltage on all 4-pin coil connectors = 12.16v
    * Checked accessory power voltage on p-side injector connectors = 12.4v
    * Swapped fuel injectors 6 and 2
    * Cleaned all injector and coil connectors with contact cleaner
    * Vacuum leak test with unlit MAPP gas torch (no effect)
    * Vacuum leak test with intake/throttle cleaner (inconclusive)
    * Swapped coils between 6 and 1
    * Vacuum leak test with unlit propane torch (extensively, no effect)
    * Removed right valve cover and inspected rockers and springs
    * Rechecked compression on #6 = 175 psi

    Anything else I can try? Below are a couple videos of what I'm seeing.

    Suggestions, guides or advice would be greatly appreciated. Thank you.


    http://<a href="https://youtu.be/mJP...JPBTEf1aLM</a>

    http://<a href="https://youtu.be/dlq...lqRMbwR_zs</a>
    Last edited by RuLEoF2; 07-13-2019 at 05:58 AM.
    2009 G8 GT
    Passion Red
    Sport Package
    Vararam CAI
    Borla Exhaust

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