Need help with a misfire/stuttering issue.
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  1. #1
    FST Member clickst's Avatar
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    Need help with a misfire/stuttering issue.

    Car:
    2018 Focus ST 3
    Mods:
    Borla Catback exhaust
    Miles:
    ~6000-7000
    Fuel:
    91 Octane from Mobil
    Cobb AP Tune:
    Stage 0 (stock)


    The problem:
    For the last 2-3 months my car has been displaying a random misfire/stutter. The car will lose power, stutter badly (to the point where I can barely get moving), and make strange noises. It doesn't matter if its a hot/cold day, car is cold or warm, fuel is full or empty, AC is on or off, gear, could happen multiple times in a day, could go a week with no issue. I have been paying very careful attention to try pin point something to identify the issue by. Only thing I have managed to see is that it tends to happen more frequently after cruising on the highway for a while, take the exit and sit at a light for a minute or two, then pulling off again it will sometimes stutter (as I mentioned this could happen everyday, or not at all for a week). Additionally when it does stutter my throttle input seems to matter very little. After taking it Ford a few times and them not being able to reproduce the issue (annoying randomness) I decided to get a Cobb AP to do some data logging.

    I am not entirely sure what to look for or what to monitor so I have the default monitor list with the addition of the "Misfire" counter(easy to see the time it spikes up). I have it plugged in and would wait for it to stutter and try recording at the next light (If it stuttered at the previous light the chances for it to stutter again briefly afterwards is high). I managed to get one of these recently and would like to ask if anyone could help look at this, tell me what I should be logging, and what the issue is. Its been very frustrating for me.

    Here is a link to the logs I took: https://drive.google.com/file/d/1x8W...ew?usp=sharing
    Special notes on logs:
    • Example where the misfire jumps from 70-80.
    • Not WOT (i can't get WOT in this situation and I am afraid of the damage it could cause if I force it)



    Thanks!

  2. #2
    FST Member jalv91's Avatar
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    I guess let the dealer have for a few days if you can manage.
    Last edited by jalv91; 05-09-2019 at 10:43 PM. Reason: Ohh you already tried dealer.

  3. #3
    FST Member clickst's Avatar
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    Quote Originally Posted by jalv91 View Post
    Well being that your car is still like brand new, I would take it to the dealer instead of trying to fix it.

    Sent from my ONEPLUS A6013 using Tapatalk
    As I mentioned, I did, but they cannot reproduce the issue due to how random it is (sent it to them 3 times now for multiple days). Since they cannot see any issues during the time they send the car back to me saying everything is fine.

    If these logs can point me to something I can take it back to them and ask them to look at something more specific.
    Last edited by clickst; 05-09-2019 at 10:48 PM.

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  5. #4
    FST Member jalv91's Avatar
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    Weird that there is no check engine light on.

    Sent from my ONEPLUS A6013 using Tapatalk

  6. #5
    FST Member clickst's Avatar
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    Quote Originally Posted by jalv91 View Post
    Weird that there is no check engine light on.

    Sent from my ONEPLUS A6013 using Tapatalk
    No check engine light, and no error codes. Its very confusing because in the car it feels very very wrong.

  7. #6
    FST Member jalv91's Avatar
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    Well if it was a misfire a cell should pop up. Maybe bad gas ? Hopefully other members Input, I'm just as stumped as you.

    Sent from my ONEPLUS A6013 using Tapatalk

  8. #7
    I spend too much of my life on FST! xTheMan42's Avatar
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    Specific gears you notice this more in? Have you checked the plugs for potential gap issues? Does the stuttering occur during gear shifts, or well after you've been driving in a selected gear?

  9. #8
    FST Member clickst's Avatar
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    Quote Originally Posted by xTheMan42 View Post
    Specific gears you notice this more in? Have you checked the plugs for potential gap issues? Does the stuttering occur during gear shifts, or well after you've been driving in a selected gear?
    Usually in 1st,2nd,3rd gear after shifting, while trying to pick up speed (usually no to very low boost), not sure if that's just due to using them more frequently between lights. Once the car is moving (30mph+) it only sometimes stutters if I ask for a lot of power, I have had it stutter on the freeway in 4th and 5th when over taking. As for the spark plugs I explicitly had the dealership check and replace them on the 2nd visit since that seems to be the most common issue. It seemed to help for a week or so before it stuttered again (this could just be luck).
    Last edited by clickst; 05-10-2019 at 10:54 AM.

  10. #9
    I spend too much of my life on FST! xTheMan42's Avatar
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    Quote Originally Posted by clickst View Post
    Quote Originally Posted by xTheMan42 View Post
    Specific gears you notice this more in? Have you checked the plugs for potential gap issues? Does the stuttering occur during gear shifts, or well after you've been driving in a selected gear?
    Usually in 1st,2nd,3rd gear after shifting, while trying to pick up speed (usually no to very low boost), not sure if that's just due to using them more frequently between lights. Once the car is moving (30mph+) it only sometimes stutters if I ask for a lot of power, I have had it stutter on the freeway in 4th and 5th when over taking. As for the spark plugs I explicitly had the dealership check and replace them on the 2nd visit since that seems to be the most common issue. It seemed to help for a week or so before it stuttered again (this could just be luck).
    When you shift into, say 2nd, what speed are you accelerating? You said no boost, so I assume it isn't hard accel. What speed for 3rd?

    Sorry, I'm just trying to picture your driving style to see how it all makes sense in my head as to what could cause stutter.

  11. #10
    FST Member clickst's Avatar
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    Quote Originally Posted by xTheMan42 View Post
    When you shift into, say 2nd, what speed are you accelerating? You said no boost, so I assume it isn't hard accel. What speed for 3rd?

    Sorry, I'm just trying to picture your driving style to see how it all makes sense in my head as to what could cause stutter.
    Very casual, shift gears around 3000 rpm, throttle not more than maybe 40%, not dropping the clutch or riding it excessively.

 

 
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