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Discussion Starter · #1 ·
I have a 2012 skyactiv. I'm getting this code which suggests a cylinder 2 misfire was detected. 95k miles. NGK Plugs have maybe 10k on them. I never got this code before doing the plug change, but now it comes and goes from time to time. I'm noticing no performance issues. If I clear the code manually it might go away for a month, or a week, then come back. When I first got the code I swapped coils between cylinder 2 and 3. Code still came back as being on cylinder 2. Eventually I bought a brand new plug, replaced cylinder 2, and again swapped the coils just for the hell of it, between 2 and 4. I used dielectric grease in the boot each time I pulled it. Any advice as to what to look at next?

I've found this TSB (https://www.cars.com/articles/2012-2013-mazda3-misfire-issue-1420683403725/), I'm out of both the powertrain and emissions warranty at this point. Would spraying intake cleaner be useful?
 

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You eliminated the chance it could be spark by swapping coils and plugs. It could be a lack of compression. But probably not. It could be a lack of air. But probably not. It could be a lack of fuel. Hmmm. As a matter of fact, I had a P0302 on an old Chevy 4.3L V6. It turned out to be the injector.

What do the long and short term fuel trims look like? Is the O2 sensor cycling properly? How many misfires?

If cyl 2's injector is not squirting, the engine will run lean. The O2 sensor will detect it. It send the too lean signal to the computer. The computer knows to add fuel when it get the too lean signal. I don't think a single cylinder can be enriched so it tries to dump more fuel into all the cylinders. That will cause a rich condition. And the cycle repeats.

When the computer turns the check engine light on it also stores a freeze frame of the data when the error was generated.

Here's a report from my Mazda3 when it was only a few months old:
http://lvhost2.com/car/OBDLinkdiagMz.html

Here's a report from my Chevy with a P0302:
http://lvhost2.com/car/Diagnostic%20Report%202017-07-22.html
Notice how the fuel trims are out of whack.

The reports were generated with the android app that comes with the ODBLink odbii adapter. It also comes with windows software that is more thorough but its a pain to take the laptop out to the car.
 

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Discussion Starter · #4 ·
Thank you, I just ordered an ODB bluetooth reader, I had been meaning to get one as my handheld unit only tells me the CEL codes and nothing more. This gives me some great ideas for what to look for next.
 

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Thank you, I just ordered an ODB bluetooth reader, I had been meaning to get one as my handheld unit only tells me the CEL codes and nothing more. This gives me some great ideas for what to look for next.
I think that is money well spent. Let us know what it finds.
 
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