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Discussion Starter #1
Hi all,

I recently purchased a 2013 Forester and after about 600 miles of driving I got a check engine light for cylinder 4 misfiring. The light came on after a hard acceleration / high RPMs.

Steps taken so far:
  • Swapped the coil packs and no changes to the codes
    • I tried to clear the codes and there were no changes to the check engine light, so I suspect it was misfiring pretty consistently on cylinder 4 or the reader was no clearing properly
    • Looking back now I don't think I revved it high enough to really test the coil pack
  • Replaced the spark plugs - Cylinder 4 spark plug looked really bad so I really thought this would fix it
  • 95% sure cylinder 4 coil pack is on a different cylinder now. Might need to revisit
  • Cleared the codes after the spark plugs
  • Took it for a test drive and when I revved it high again (6k) the light came back on for cylinder 4 misfire
  • Cleared the codes again and revved the engine up to 4k in the garage and the light came back on for cylinder 4 misfire
  • Guy at Autozone said it might be bad gas (Arco 87) - I doubt this would just effect cylinder 4 though
Any advice on next steps?
  • I might swap coil packs again just to double check
  • I tried to follow the wiring but it seems to merge up with other wiring? How hard is it to replace the wiring to the coil packs?
  • Might try better gas and injector cleaner?
Thanks for any help!
 

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1999 "L" - 231,000 mi. AT
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Guy at Autozone said it might be bad gas (Arco 87) - I doubt this would just effect cylinder 4 though

Thanks for any help!
Absolutely try better gas, that's a cheap test. Don't think ARCO is really up there in quality; try toping off your current tank with Shell Premium.

But the check engine light, only? ... can you feel that it's missfiring?
 

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Discussion Starter #3
@UhOh Thanks for the suggestion I'll try Shell Premium. Maybe run some injector cleaner through as well?

I didn't notice the misfiring - no power pulsing while driving and no heavy smell of unburnt fuel
It did seam to be idling rough at low RPM but assumed this was due to ECU reset after having the battery disconnected for awhile
Any other telltale signs for misfire?
 

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Discussion Starter #4
Posting a picture of the spark plug from cylinder 4 for reference and if anything can be diagnosed from it.
Have a new theory - maybe the injector is not delivering a enough fuel? Spark looks like it might be running lean in this cylinder?
Added some shell premium fuel but haven't really driven it around yet to see if it keeps misfiring.
PXL_20201019_220541179.jpg
 

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2012 Forester 4 speed auto
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Do a compression check on cylinder #4. If it reads normal, do a running compression check which should read one half the static compression check pressure. This will eliminate an expensive mechanical cause of the misfire.
 

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Discussion Starter #6
I swapped the injectors today to see if it would move the code from cylinder 4, will see what happens the next time the check engine light comes on.
I'll check the compression next, I think I read one of your other posts saying anything under 100 is a huge problem.
 

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Discussion Starter #7
Engine light came back on and it's still cylinder 4 so don't think it is the injectors. Checking compression next
 

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Discussion Starter #8
Do a compression check on cylinder #4. If it reads normal, do a running compression check which should read one half the static compression check pressure. This will eliminate an expensive mechanical cause of the misfire.
Cylinder 4 is reading low at 90 PSI - I am assuming a leak down test is next?
 

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2011 Forester
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Yup, I had the same problem with my 2011 Forester in cylinder two. Ended up needing to have the cylinder shaved even and new gaskets. Solved my misfire and the cel.
 

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Discussion Starter #10
@toommm Thanks for the input, were you able to diagnosis the cylinder issue with a leak down test? How much did it end up costing?
 
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