on going cylinder 4 misfire

Discussion in 'Mazdaspeed 3/6 Engine' started by jesus, Apr 2, 2021.

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  1. jesus

    jesus Greenie N00B Member

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    For the longest now ive been having a cylinder 4 misfire that will come and go out of random. Ive gone through and replaced a ton of hardware( spark plugs/coil packs/wiring harness/fuel injectors and seals/ fuel rail and injector harness/) only time I've noticed a difference of the problem becoming less frequent is when gaping cylinder 4 to around .23-.25 anything higher then that and it seems to just hate it and starts acting up. At a loss here and any info or advice would be greatly appreciated. Data logs can be provided as well if needed.
     
  2. Raider

    Raider Administraider Administrator Platinum Member

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    Compression and leak down test is next.
     
    Raider, via an iPhone, Apr 2, 2021
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  3. Awafrican

    Awafrican Moderator Gold Member

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    As raider said.

    But why are your gaps .23-.25" they should be 026-.028"
     
    Awafrican, via a mobile device, Apr 2, 2021
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  4. Easter Bunny

    Easter Bunny Professional Engineer Platinum Member

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    I hope that was a typo
     
    Easter Bunny, via a mobile device, Apr 2, 2021
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  5. jdr767

    jdr767 Platinum Member

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    You've done the "bunny hop" with the plugs and boots and kept track? ie: plug from 4 goes into cylinder 2, boot goes on cylinder 3 and make sure the problem stays on cylinder 4?
     
  6. Awafrican

    Awafrican Moderator Gold Member

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    Me too
     
    Awafrican, via a mobile device, Apr 6, 2021
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  7. jesus

    jesus Greenie N00B Member

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    Finally got some free time and was able to find, after a some diag the root of the issue, the ground wire pin for cylinder 4 was completely pushed into the connector causing it to short out the spark. I went ahead and changed out the engine harness with one i had laying around and it hasn't misfired yet ever since then. Also in response to the plug gap i meant .26

    Compression 165-150
    1 - 160
    2 - 165
    3 - 150
    4 - 150
    Leak down 5-15%
    1 - 10
    2 - 5
    3 - 15
    4 - 10
     
    Last edited: Apr 12, 2021
  8. Awafrican

    Awafrican Moderator Gold Member

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    .26" is waay to big, should be .026-.028"

    Glad the misfire is gone, engine seems to have had better days
     
    Awafrican, via a mobile device, Apr 12, 2021
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