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Random misfire and Misfire cylinder 8

Discussion in '5.0L Coyote V8 Engine Modification/Discussion' started by Voidedwarranty, Dec 13, 2016.

  1. Voidedwarranty

    Voidedwarranty New Member

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    Dec 13, 2016
    2016 Mustang GT with 11,000miles.

    Get ready for the facepalm. I am not proud of this, but looking to hopefully get an answer.

    I was running my 93 tune and a friend had convinced me that running 5gallons of e15 along with 11gallons of 93 would be good enough to feel a slight power increase. I was skeptical at first, but I ran it anyways.

    I ran the tank down to nearly a quarter tank and I received my first code the next morning when the motor was cold. Continued to run the tank down to nearly empty and refilled with 93 completely after seeing the misfire code.

    Clear code and car runs normal, no loss of power for the entire day. Park it over night, begin my journey to work and on a decel the code comes back. I am at about a half tank now from refilling completely with 93. Clear the code and the car runs normal. Runs normal when the code is present as well.

    Pulled #8 spark plug this morning and did not notice any oil on the threads. Pulled the next plug up which I believe is #7 and found that it looks exactly the same as 8 did. So I swapped coils hoping the misfire would follow the coil. I had done this several hours ago and will more than likely have to wait until the morning to see if the car will misfire again, because like I said once the car has gotten its morning out of the way, the problem is absolutely nonexistent.

    Is this a fuel related issue and its working its way out, or is the cylinder getting ready to throw the code every chance it can, causing me to get ready to whip out the check book.

    Again, not proud of this so please keep the comments on the knowledgeable side.
     
  2. Swetrid

    Swetrid Member Established Member

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    Reading Pa
    Technicians on the Ford message boards have been reporting broken intake manifold runner controls causing P0300 and P0308. I assume the butterfly part in the intake is the problem.
     
  3. Voidedwarranty

    Voidedwarranty New Member

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    Thank you Swetrid. Is this something that only requires dismantling the intake manifold or would I need to dig further?

    Those are the exact codes I'm getting. This morning on my way into work, I did not get the codes because I never let the car cruise in 6th gear at whatever rpm the 3.73's put down.

    Is the intake manifold a serviceable part or would it be better off being replaced by an aftermarket at this point?
     
  4. daustin

    daustin Member Established Member

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    If it is the manifold/IMRC's, you can buy complete new take off 2015+ manifolds (with IMRC actuators) from shelbyauctions (Shelby) on eBay for $20-30. Sometimes they will also throw in the TB for the same price as well. I paid $19.99 total (plus tax as I'm local to Shelby) for the complete manifold assembly including all vacuum lines and TB back in October. I bought it for my father-in-law's friend that wanted to take his Roush off to sell his car and he no longer had the stocker.
     
  5. Voidedwarranty

    Voidedwarranty New Member

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    Thank you daustin. Its good to know these types of things. Frustrating to say the least because I dont want to damage the engine, but the code isnt persistent enough for me to think I've done anything past the manifold.
     
  6. Vantango

    Vantango New Member

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    Jul 26, 2017
    i'm have same problem, P0300, P308 codes. dealer has had car 4 days, finally replacing intake manifold, is what service writer said.


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  7. Vantango

    Vantango New Member

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    if anyone has any thoughts let me know, hope this solves problem. still under warranty.


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  8. whatsup62

    whatsup62 Member Established Member

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    Iowa
    Did the same thing..had the same codes...fill it up with 93 NOW.
     
  9. Vantango

    Vantango New Member

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    i run ethanol free fuel 93 , so here is verdict.... ended up replacing intake manifold runner control along with new manifold gaskets....apparently it broke.


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  10. Vantango

    Vantango New Member

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    and for the long version..The intake manifold runner control is an engine management component that is found on newer intake manifold designs. It is usually a motorized or vacuum actuated unit attached to the intake manifold, that controls the opening and closing of butterfly valves inside of the intake manifold runners. The unit will open and close the butterfly valves in order to provide maximum manifold pressure and flow at all engine speeds.

    While an intake manifold runner is not necessary for engine operation, it does provide the engine with increased performance and efficiency, particularly at low engine speeds. When the intake manifold runner control fails, it can leave the engine without the increased performance, and in some cases even reduce performance. Usually a faulty intake manifold runner control will produce a few symptoms that can alert the driver of a potential issue.


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  11. Mariolow11

    Mariolow11 New Member

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    I have a 2017 GT with 34K miles. It is at the dealer now with the same codes thrown(P0300, P0308). Apparently, my number 2, 4, & 8 cylinders are burnt, and they need to replace the head. They are still not sure what caused it though. They are waiting on Ford to verify before fixing.
     
  12. MastaAce03

    MastaAce03 Active Member Established Member

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    Seattle
    All stock? That's crazy. They should be replacing both heads/ a whole new long block considering you had cylinder damage on both side of your block.


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  13. Mariolow11

    Mariolow11 New Member

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    Ya, completely stock. All I have is a catback. If I had it my way, they would just replace the whole engine.

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  14. MastaAce03

    MastaAce03 Active Member Established Member

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    They definitely should be considering they don't know why or how it happened. Stay firm and respectful and you have a hell of a argument to replace the whole thing.


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  15. Mariolow11

    Mariolow11 New Member

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  16. Mariolow11

    Mariolow11 New Member

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    Got my car back today. It was the intake manifold runner control on the secondaries. the control unit was broken, allowing more/less air into the cylinder, causing said cylinder to misfire.
     

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