Join Date: Jun 2010
Location: Boston, MA
Car Year: 2010
Car Model: Forester
Feedback Score: 0 reviews
Since the code has returned, take a look at the freeze frame data, specifically, the short term/long term fuel trim numbers (Both banks) as well as the rpm & load numbers.
If the STFT and LTFT numbers are OK (for both cylinder banks, but especially bank 1), then the problem is less likely to be ignition related and probably air/fuel or compression. LTFT numbers should be within +/- 10 to 15%.
If outside of this range, then the PCM is correcting for an overly rich/lean condition -- what you're looking for here is an indication if the misfire is being caused by a rich or lean problem which have different troubleshooting approaches. E.g., excessively rich could be a bad fuel pressure regulator, leaky fuel injector, etc. Excessively lean could be an intake leak, etc.
A mechanical condition may exist (e.g., burnt exhaust valve), so in addition to the compression test, do a leak down test on the cylinder. If your shop has an oscilloscope, they can do a relative compression test. Good luck.
10 Forester X Prem AT, 07 Boxster S, 03 MB E320