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Discussion Starter · #1 ·
I recently purchased a used 2015 focus st to replace my problematic bmw 335i. It came from the dealership with about 39k miles on it. I’ve absolutely loved the car and am up to 41k on it already.
On the way to work today I noticed a flashing cel while cruising in 6th. Although there wasn’t a solid light present on the dash, I have been scarred from how unreliable my bmw was. I immediately got my ecu scanned to try and prevent any further damage. Autozones scanner read a cylinder 2 misfire. The first thing I did was change out the spark plugs. After doing that, I rescanned the car and the ecu no longer displayed a misfire. However I can still feel and hear slight misfires in the low rpm range in reverse and first gear.
I added a photo of the old spark plugs. I will say that the plugs I pulled were NGK Iridium LTR7IX-11 plugs (I think these are one step colder plugs) and I reinstalled NGK Iridium LTR6IX plugs. Should I be worried? And what other steps can i take in fixing my slight misfires?
 

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  • Those old plugs are heavily fouled
  • As above, what did you gap them to?
  • What mods are on this ST? Are you tuned?
These engines are reliable when treated properly and maintained. User education, however, is the problem point. Lots of the issues that occur with these vehicles are lack of knowledge or proper care.
 

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Discussion Starter · #5 ·
  • Those old plugs are heavily fouled
  • As above, what did you gap them to?
  • What mods are on this ST? Are you tuned?
These engines are reliable when treated properly and maintained. User education, however, is the problem point. Lots of the issues that occur with these vehicles are lack of knowledge or proper care.
The gap on the new plugs were .027. I do not have a tune, but the previous owner had a Cobb intake and awe exhaust installed. The sound symposer was still there when I bought the car and I didn’t really like the cabin sound, so I put in a delete kit a few days afterwards. The cars quite new to me so I haven’t checked for an upgraded motor mount, but the car is stock other than that. Should I assume from the intake and spark plugs that the previous owner tuned the car?
 

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The gap on the new plugs were .027. I do not have a tune, but the previous owner had a Cobb intake and awe exhaust installed. The sound symposer was still there when I bought the car and I didn’t really like the cabin sound, so I put in a delete kit a few days afterwards. The cars quite new to me so I haven’t checked for an upgraded motor mount, but the car is stock other than that. Should I assume from the intake and spark plugs that the previous owner tuned the car?
Plugs, maybe. Intake? No. Technically you can run either without a tune. Intake won't do anything for performance.

Generally for tuned setups, plug gap is recommended to be .026.

Another note, cold start misfires are normal to a degree. Is it misfiring all the time, or just before it's warmed up?
 

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Discussion Starter · #7 ·
Plugs, maybe. Intake? No. Technically you can run either without a tune. Intake won't do anything for performance.

Generally for tuned setups, plug gap is recommended to be .026.

Another note, cold start misfires are normal to a degree. Is it misfiring all the time, or just before it's warmed up?
The car seems to be misfiring at a low rpm range upon acceleration in first and while in reverse. It almost sounds like the car is backfiring, but it’s a subtle sound, You can hear it more clearly with the windows open. It happens when the car is cold and continued after the car warmed up.

What should I be gapping my plugs at for running the car stock?
 

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That gap should be fine and normally it will only miss under high boost with a big gap on the plugs. Yours doing this at low rpm and boost, is not gap related. Maybe coils?
 

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I recently purchased a used 2015 focus st to replace my problematic bmw 335i. It came from the dealership with about 39k miles on it. I’ve absolutely loved the car and am up to 41k on it already.
On the way to work today I noticed a flashing cel while cruising in 6th. Although there wasn’t a solid light present on the dash, I have been scarred from how unreliable my bmw was. I immediately got my ecu scanned to try and prevent any further damage. Autozones scanner read a cylinder 2 misfire. The first thing I did was change out the spark plugs. After doing that, I rescanned the car and the ecu no longer displayed a misfire. However I can still feel and hear slight misfires in the low rpm range in reverse and first gear.
I added a photo of the old spark plugs. I will say that the plugs I pulled were NGK Iridium LTR7IX-11 plugs (I think these are one step colder plugs) and I reinstalled NGK Iridium LTR6IX plugs. Should I be worried? And what other steps can i take in fixing my slight misfires?
I have a similar issue with my 17 but mines only on start up for a few seconds and mine's cyl 4 all my plugs look the same as yours. Ive changed all my coil packs, and all my plugs. I dont wanna dig to deep, in fear of making it worse. Im taking it in to have some maintenance done and that looked at. If they can find the issue ill let you know what it was, it may help you with yours.
 

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Discussion Starter · #10 ·
I have a similar issue with my 17 but mines only on start up for a few seconds and mine's cyl 4 all my plugs look the same as yours. Ive changed all my coil packs, and all my plugs. I dont wanna dig to deep, in fear of making it worse. Im taking it in to have some maintenance done and that looked at. If they can find the issue ill let you know what it was, it may help you with yours.
Hey man, sorry, I’m just seeing this but what i found out was the factory spark plug gap on the NGKs are a bit too wide for the st. I regapped them down to .027 and haven’t noticed an issue since. I also went ahead and replaced my second cylinder coil preventatively since I was having a misfire there.
 

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Discussion Starter · #11 ·
And to clear up any confusion, I was incorrect above about the plugs coming from the factory with .027 gap. When I pulled the plugs to check them again the gap on the NGKs were actually more around .031
 

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And to clear up any confusion, I was incorrect above about the plugs coming from the factory with .027 gap. When I pulled the plugs to check them again the gap on the NGKs were actually more around .031
That is the Ford gap recommendation...not good!
 
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