rough running, cyl 1&2 misfire

[myribitsbroke]

2007 Forester 4-cyl manual NA



CEL and flashing cruise came on, figured it was because it was overdue
for an oil change. Off and on, but most of the time on. Went off when
changed the oil but came back a day or two later. Suddenly begins to run
very rough and CEL begins to flash on way home.

Codes:

p0420 (cat efficiency low)

P0301 (cyl 1 misfire)

P0302 (cyl 2 misfire)

and the MIL readings:

Misfire

Fuel

Comp

Cat

Evap

O2 Sensor

O2 HTR

EGR



quite a list. where to start? are some of these codes being thrown on
account of the more serious codes (ie misfire causing o2 sensor reading
to be funky, etc)

[Fairtax4me]

Those are emissions monitors that are set as part of the emissions testing readiness checks. Nothing to worry about there.

P0420 is probably on because of the misfires. Probably just needs new spark plugs. How many miles on the engine, and when were the plugs changed last, if they've ever been changed?

[myribitsbroke]

the engine has about 128k bought it in august with 115k not sure if/when last time plugs were changed but will start there.

[Fairtax4me]

Yeah, start with NGK plugs, and either Subaru or NGK spark plug wires if it isnt coil-on-plug. Might do some other basic tune-up stuff too like fuel and air filters and change the PCV valve.

[myribitsbroke]

put new spark plugs in today. the old ones didn't look that bad although the passenger side rear plug (sry, i'm new to subarus, don't know which cylinder that is) had a little bit of oil on it. the gap didn't look noticeably out of spec. once installed i started the car again and it still runs like garbage.

[Fairtax4me]

That would be number 3.

 

3------4

1------2

Front

 

The valve cover grommet is leaking and will need to be replaced fairly soon or it will short that spark plug and cause misfires. That could possibly be a cause of the current misfiring.

 

Does that engine have spark plug wires or individual coils mounted directly on the plugs?

[myribitsbroke]

FairTax-

 

it has spark plug wires. i found a video that advised turning the wires almost 180 degrees before removing in order to keep the metal contact in tact so i did that. how are you sure that the valve cover grommet is leaking?

[Fairtax4me]

That's the only source of oil in spark plug wells. If it were another leak it would make a huge mess all over the engine before getting into the plug well.

 

Have never heard of twisting plug wires. Kinda sounds like bird to me.

Swap the plug wires front to rear and see if the misfire codes follow them. Or if they look old just replace them.