I know that individually the P0301,P0303 & P0305 are cylinder misfire codes. But what would cause all three in one bank of cylinders to register a misfire at the same time?
Thanks in advance.

bad would be head gaskets. maybe a fuel rail issue though. or a o2 sensor.

ever overheat ?

 

No signs of a head gaskets issue. Never overheats. Which O2 sensor should I check, pre or post cat?

 

pre-cat but possibly post cat.

o2 sensors failing can retard things causing misfires.

others will post up batter ideas:
but you can check these out

Subaru Factory Service Manuals (FSM) - Every Model - USDM/EU

A home for die hard Subaru Legacy, Outback and Baja fans!

sl-i.net

 

Could also be a throttle body issue.

 

How so?

 

Fuel pressure regulator. It's on the rail on one side, and if it is leaking, the cylinders on that side will be seeing different fueling than on the other side, leading to misfires on one side or the other, depending on how the ECU attempts to correct the AF ratio.

 

So there's only one fuel regulator?

 

vvt solenoids passenger side. fuel pressure regulator is in the fuel tank. All recent subaru h6 are sequential multi port fuel injection and have 1 injector per cylinder

 

Mine is a 2010 though.

 

Depending upon which platform you prefer to use, this: Amazon.com: OBDLink LX OBD2 Bluetooth Scanner for Android and Windows: Automotive

Or this:

Amazon.com: OBDLink MX+ OBD2 Bluetooth Scanner for iPhone, Android, and Windows : Automotive

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smile.amazon.com

 

the OBD link XX series are bad. their software does not properly shut down the adapter and I am constantly having to hit the reset button... also their limitation to 4 graphable items at once sucks

 

you will most likely get a p420 or fueling error code or a heater circuit problem. Misfires on one bank are typically VVT solenoids. I did mine at 160K and it cleaned my idle right up on my 3.6R. no matter the miles on your oil change, Subaru and other manufacturers state to change oil with VVT solenoids. I did just that.