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Discussion Starter #1
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/1x8WN3DOAwjPOgtBNBqh6CO58M1AhZChQ/view?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!
 

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Discussion Starter #3 (Edited)
Well being that your car is still like brand new, I would take it to the dealer instead of trying to fix it.

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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.
 

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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
 

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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?
 

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Discussion Starter #8 (Edited)
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).
 

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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?
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.
 

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Discussion Starter #10
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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I would still check the plugs myself. I've seem the stealerships they test drive your car everything seems fine they call it good and don't even check anything else.
 

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Plugs are a good maybe, like was said above, I would just check them, it's pretty quick and easy which is good because these cars go through plugs more often than others.

What kind of MPG are you getting? Any fluctuations since this problem?

I've had an unplugged coil before that made it run like crap but it was constant instead of intermittent so I doubt that is it......I'm stuck on spark plugs right now. These cars are awesome but are picky on plug gap and fuel as I have found out personally. Hope you find the problem fast so you can enjoy your ST!
 

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Discussion Starter #13
Checked the gaps as follows:

Plug 1: 0.036
Plug 2: 0.034
Plug 3: 0.035
Plug 4: 0.037

Re-gapped them all to 0.032

Also notices they were fairly black around the rim, not sure if that is normal or not.
I will take the car out for a drive later to make sure it at least runs ok with this change. And if it does then I will monitor for any improvements. As mentioned before this was very random so it might be a while till I see the issue if its still there.
 

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Checked the gaps as follows:

Plug 1: 0.036
Plug 2: 0.034
Plug 3: 0.035
Plug 4: 0.037

Re-gapped them all to 0.032

Also notices they were fairly black around the rim, not sure if that is normal or not.
I will take the car out for a drive later to make sure it at least runs ok with this change. And if it does then I will monitor for any improvements. As mentioned before this was very random so it might be a while till I see the issue if its still there.

I'm pretty sure even on a stock vehicle you can close up the Gap a little and run a step colder plug. I gap my plugs to .026. but I am stage 3. Since you have the AP why not throw a green filter on and run a stage 1 tune. Or even throw on and fmic. Which of these cars really need anyway. And go stage 2? Anyhow I'm pretty sure you'll see an improvement.
 

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Discussion Starter #16
I'm pretty sure even on a stock vehicle you can close up the Gap a little and run a step colder plug. I gap my plugs to .026. but I am stage 3. Since you have the AP why not throw a green filter on and run a stage 1 tune. Or even throw on and fmic. Which of these cars really need anyway. And go stage 2? Anyhow I'm pretty sure you'll see an improvement.
I was planning on getting the mouttune mp275 package (and in the future probably more) but wanted to solve this problem before adding more confusion into the mix. I figured it was better to upgrade after I know the car is running optimally.
 

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I'm pretty sure even on a stock vehicle you can close up the Gap a little and run a step colder plug. I gap my plugs to .026. but I am stage 3. Since you have the AP why not throw a green filter on and run a stage 1 tune. Or even throw on and fmic. Which of these cars really need anyway. And go stage 2? Anyhow I'm pretty sure you'll see an improvement.
I was planning on getting the mouttune mp275 package (and in the future probably more) but wanted to solve this problem before adding more confusion into the mix. I figured it was better to upgrade after I know the car is running optimally.

That's understandable.
 

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Those plugs were fairly clean, but those gaps before you re-gapped were atrocious.

Let us know how it's running since then.
 
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