Misfire/backfire

Discussion in 'Generation 4 - Maintenance & Troubleshooting' started by TomahawkSHO, Aug 15, 2019.

  1. TomahawkSHO

    TomahawkSHO SHO Member

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    2014 non-PP. LMS 93 3 bar perf tune, catless DP. 82K miles.

    Went to pass someone last night and as I got up to higher RPMs and about 70mph the car backfired enough to where the check engine light flashed for about 10 seconds. The car has had some "hesitation" at highway speeds when accelerating at WOT. On WOT starts I've had some backfire/misfire type behavior, but never had the check engine light flash during an event like that. I've been wanting to change to colder plugs and I mat do that first to see if I discover the problem in the process. Any input would be appreciated.
     
  2. krewat

    krewat SHO Member

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    You're running stock plugs? And while you're in there, clean the MAP sensor, and the sensor on/before the throttle body (it's a 3bar MAP, but it's called something else by Ford, and I forget what it is) ;)
     
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  3. TomahawkSHO

    TomahawkSHO SHO Member

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    Yep stock plugs. It's pretty dirty under the hood right now as well. Will do!
     
  4. Lostneye

    Lostneye SHO Member

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    LMS recommends stock plugs but change every year of 20k miles IIRC. These motors are sensitive to plugs. How many miles on them? Agree with krewat to clean the MAP sensors. Also what LMS tune? Their V11 has issues and is downright dangerous in colder weather. Personally I would, and have switched to a different tuner.
     
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  5. TomahawkSHO

    TomahawkSHO SHO Member

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    Original plugs so those are being changed. I do believe I'm running the V11 tune. What issues have people been having? I did briefly look into the gearhead tunes but the money to switch hasn't been in the cards.
     
  6. Lostneye

    Lostneye SHO Member

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    Clean the MAP sensors while you are there.

    LMS likes to run rich so fuel pressure can be an issue, dangerously so in the cold. I have a log with fuel rail pressure dropping to 800 PSI. If you have hesitation issues or missed 2-3 shift keep your foot our of it until you can switch tunes. A lot of people also have missed 1-2 shift unless you turn traction control off. LMS has updated tunes howver they make less power to keep fuel pressure safe. I am very happy with Gearhead, no fuel pressure or missed shifts.
     
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  7. TomahawkSHO

    TomahawkSHO SHO Member

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    I have an occasional hesitation issue when accelerating hard from 60+. What power are you making with the gearhead tune?
     
  8. Lostneye

    Lostneye SHO Member

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    I would see if you can datalog, either a friend with an SCT you can borrow, I know forscan can log but never tried it. The highway is where I noticed hesitation and after seeing some issues on here decided I couldn't take the chance. From a dig I never felt hesitation including my last pull with LMS that I logged before switching tunes that showed dangerously low fuel pressure. I haven't been to the track with the GH tune, someone on here dynoed both LMS 93 tune and GH AO tunes and GH made slightly more power.
     
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  9. TomahawkSHO

    TomahawkSHO SHO Member

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    I did about 8 runs at an 1/8 mile track last weekend. After the first two i didn't have any issues with mis/backfires.
     
  10. SM105K

    SM105K Land Yacht Pilot Supporting Member

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    GET RID OF V11! There are numerous posts on this site about how junk that tune is. Fuel pressure problems, back fires, miss shifts ect.
     
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  11. SHOdded

    SHOdded SHO Member Supporting Member

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    For misfires, it is usually plugs or injectors. Tuned, you gotta watch the plugs like a hawk, as mentioned above. When you pull the old ones out, be sure to take good pics and post them in this thread. Hopefully all are burning correctly, and there are no fuel or oil telltale signs.

    If you see oil, it is either a leaky valve cover gasket or the PCV system.
     
  12. shoblock

    shoblock SHO Member

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    V11 was my problem, 100%. I was convinced the engine or transmission was going to blow from driveability issues. Went to Gearhead auto-octane in January and have not had a single issue since.
     
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  13. twobitcoder

    twobitcoder Member

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    If your tuned boosted car backfired then your engine is already damaged due to air fuel ratio failure. A backfire on such an engine is not just a "oops" situation. It's a "stop driving immediately" situ, as in, equal to a pegged heat gauge.
     
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  14. yaycandy

    yaycandy SHO Member Supporting Member

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    Yea man i dont know. I dont want to point fingers at V11 but i had my own issues with it before i blew my engine so maybe try GH or brad for a tune and see if it still happens. Either that or install their HPFP and get a redid tune with them.
     
  15. TomahawkSHO

    TomahawkSHO SHO Member

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    Update: Changed the plugs and LMS sent me an updated tune to address any possible low fuel pressure issues. I've had zero issues since these changes. Car is running as well as I've ever felt it run in every situation. The new plugs are gapped at .030. I had about 40,000 tuned miles on the original plugs. Fuel mileage has gone up a bit. So far so good.
     

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  16. SHOdded

    SHOdded SHO Member Supporting Member

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    Plug condition looks pretty decent. Enjoy :)
     
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  17. yaycandy

    yaycandy SHO Member Supporting Member

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    New plugs and .030 gap should be right on the money with your tune. I have an upgraded fuel pump and it was best at .026-.028 for me but with your stock pump and lms actually toning it down for you, .030 should be great

    .030 was the sweet spot for me with lms v11 without a HPFP last year.
     
    Last edited: Sep 3, 2019
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  18. FiveLeeter918

    FiveLeeter918 Ortiz Performance Sales Supporting Member

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    Definitely change the plugs, sounds like you cracked the porcelain and it's arching against the head. Jump up to SP-542s gapped to 0.026" and you'll be set.
     
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  19. Rick Steinard

    Rick Steinard New Member

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    Gentlemen, I have the standard SHO with a Diablo tuner. I run the 93 tune. I did nothing else to the car. Put it in new at 4k miles. She has 126k on it now. She just started with the misfire getting on the freeway. I took the tune out and the problem went away. Put it back in and its back. So, from this thread, I am hearing spark plug change. This is my daily driver and work car. (outside sales it a 2016). The stock stuff worked before, any reason not to use it again?
    Thanks
    Rick
     
  20. SM105K

    SM105K Land Yacht Pilot Supporting Member

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    First things first, change the plugs and throw the Diablo tuner in the trash. Get a proper tuner and tune, and your car will run a lot better.
     
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