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Misfires under hard acceleration

This is a discussion on Misfires under hard acceleration within the Focus RS TroubleShooting forums, part of the Focus RS Garage category; 45k KM, '16 w/ cat back exhaust, RMM, FMIC, turbo smart BOV and WGA, Iridium step colder plugs, tuned by Adam/Tune+. Plugs were purchased from ...

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Thread: Misfires under hard acceleration

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    Misfires under hard acceleration

    45k KM, '16 w/ cat back exhaust, RMM, FMIC, turbo smart BOV and WGA, Iridium step colder plugs, tuned by Adam/Tune+. Plugs were purchased from Tune+ and gapped properly.

    I've been monitoring the misfire count through the Cobb AP. Before installing the plugs I'd see much more frequent misfires usually when idling or just normal operation, now they occur very occasionally. However, it's always been pretty typical for 3-7 misfires to occur under hard acceleration (either instant peddle mash WOT, or rolling into WOT over about a half a second). This happens only about a third of the time though, usually there's zero misfires. More common in 2nd gear than 3rd.

    First, this is bad, right? I'm not being over paranoid, this is a mechanical defect?

    If yes, then what/where should I check first? No code has ever been thrown, but when it does misfire under hard acceleration it sucks, seems like the car is hesitating. When it doesn't happen the acceleration and torque is insane.

    I'm sorry if there's already similar threads but I haven't read any resolutions for a non-CEL occasional issue like what I'm experiencing.

    The car was tuned during the winter and now it's getting warmer, Andy had asked for another batch of logs once it warmed up, how likely is it related to the temperature?



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    Mayhem2.3RS likes this.

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    Quote Originally Posted by ariens.ca View Post
    45k KM, '16 w/ cat back exhaust, RMM, FMIC, turbo smart BOV and WGA, Iridium step colder plugs, tuned by Adam/Tune+. Plugs were purchased from Tune+ and gapped properly.

    I've been monitoring the misfire count through the Cobb AP. Before installing the plugs I'd see much more frequent misfires usually when idling or just normal operation, now they occur very occasionally. However, it's always been pretty typical for 3-7 misfires to occur under hard acceleration (either instant peddle mash WOT, or rolling into WOT over about a half a second). This happens only about a third of the time though, usually there's zero misfires. More common in 2nd gear than 3rd.

    First, this is bad, right? I'm not being over paranoid, this is a mechanical defect?

    If yes, then what/where should I check first? No code has ever been thrown, but when it does misfire under hard acceleration it sucks, seems like the car is hesitating. When it doesn't happen the acceleration and torque is insane.

    I'm sorry if there's already similar threads but I haven't read any resolutions for a non-CEL occasional issue like what I'm experiencing.

    The car was tuned during the winter and now it's getting warmer, Andy had asked for another batch of logs once it warmed up, how likely is it related to the temperature?



    Sent from my Pixel 3 XL using Tapatalk
    Check your gap on your plugs.


    Sent from my iPhone using Tapatalk

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    Quote Originally Posted by Mayhem2.3RS View Post
    Check your gap on your plugs.


    Sent from my iPhone using Tapatalk
    I know you said gapped properly. But just double check


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    Quote Originally Posted by Mayhem2.3RS View Post
    I know you said gapped properly. But just double check


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    What should they be gapped at?

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    Quote Originally Posted by ariens.ca View Post
    45k KM, '16 w/ cat back exhaust, RMM, FMIC, turbo smart BOV and WGA, Iridium step colder plugs, tuned by Adam/Tune+. Plugs were purchased from Tune+ and gapped properly.

    I've been monitoring the misfire count through the Cobb AP. Before installing the plugs I'd see much more frequent misfires usually when idling or just normal operation, now they occur very occasionally. However, it's always been pretty typical for 3-7 misfires to occur under hard acceleration (either instant peddle mash WOT, or rolling into WOT over about a half a second). This happens only about a third of the time though, usually there's zero misfires. More common in 2nd gear than 3rd.

    First, this is bad, right? I'm not being over paranoid, this is a mechanical defect?

    If yes, then what/where should I check first? No code has ever been thrown, but when it does misfire under hard acceleration it sucks, seems like the car is hesitating. When it doesn't happen the acceleration and torque is insane.

    I'm sorry if there's already similar threads but I haven't read any resolutions for a non-CEL occasional issue like what I'm experiencing.

    The car was tuned during the winter and now it's getting warmer, Andy had asked for another batch of logs once it warmed up, how likely is it related to the temperature?



    Sent from my Pixel 3 XL using Tapatalk
    The Ford system is quite sophisticated and from what I understand is as follows. Even a totally healthy engine will misfire at times. If the misfire count exceeds a critical threshold that Ford deems unsatisfactory the it throws a CEL. So if no CEL then the misfire count is within whats expected from a healthy engine.
    Sometimes you can have too much information and for some people the expectation will be that perfection is the norm. I don't think that's reality. Obviously the less the better but if you're not "feeling" misfires and its not throwing a CEL then I'd say you're good.

    Ciao
    Last edited by lucky phil; 05-08-2019 at 10:29 PM.
    If you're not living on the edge you're taking up too much space.

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    RS Senior Member stvjeep's Avatar
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    Last edited by stvjeep; 05-08-2019 at 11:58 PM. Reason: Added 2nd article

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    I've read those but didn't attribute my misfires to "normal operation" given that I can actually feel the car stutter for that split second.

    Are you suggesting this is normal? Do all of ours have that occasional few misfires on hard acceleration that can be felt?

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    Possibly like what every buddy else said, sparkplug gap, possibly bad fuel, if you've filled up multiple times, it most likely isnt bad fuel, it could be fuel pressure dip. But if you arent getting a cel, it is most likely a badly gapped plug, dirty, or too cold of plug. The reason why it is most likely that, is the system only sees pre detonation, misfires, and backfires. If the fuel burned but horribly it wont care.

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    You have the NGKs?
    How many miles have they been used?
    As others have stated, have you taken the spark plugs out recently after the misfire?
    Have you ever put any oil additives in?

    Here are the recommendations from tune+ website

    0275 for 91/93/E30 and .0245" for E85

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    Supporting Member DeanHart's Avatar
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    The RS eats plugs

    Stuttering at 4k RPMs in 4th gear resolves with NEW plugs at .026
    2017 Stealth RS

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