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Old 08-11-2015, 06:24 PM   #1
mit9550
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Subaru Banner Misfire code help

I am new to the group and have a question about my daughters 2008 Impreza 2.5l. When pulling away from a stop the engine stutters and is also idling slightly rough though not terribly bad. Code showing are P-0420, dealing witht the catalytic converter and P-0303 a misfire in cylinder 3. Where should I start to diagnose the issue. The car has 92, 000 and was bought used about 3 years ago and has had no issues. But, I dont know anything about the maintenance history. Should I start with plugs, wires and coil or coul the catalytic converter be the cause of the misfire code?
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Old 08-11-2015, 06:39 PM   #2
Loyale93
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I doubt the Cat would be the cause of the misfire, but it's also a surefire fix to just replcae the cat. And also fairly easy to do yourself with a few hand tools, jack/stands/lift, and some time.

Please fill in your profile and we can direct you to a local shop if this is not something you can/want to do yourself.

Points and time-out to the first person who asks for pictures of his daughter.
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Old 08-11-2015, 07:00 PM   #3
Gallo2011
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Quote:
Originally Posted by Loyale93 View Post
I doubt the Cat would be the cause of the misfire, but it's also a surefire fix to just replcae the cat. And also fairly easy to do yourself with a few hand tools, jack/stands/lift, and some time.

Please fill in your profile and we can direct you to a local shop if this is not something you can/want to do yourself.

Points and time-out to the first person who asks for pictures of his daughter.
What about his other daughter? Apparently he has more than one.

The rear O2 sensor is also a suspect for the p0420. You should really have the sensor and the cat tested to rule one or the other out. The spark plugs are a fairly cheap replacement, so try replacing them to see if the p0303 goes away.
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Old 08-18-2015, 12:09 PM   #4
mit9550
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Thanks for the advice. I'll start with the plugs and the catalystic converter. And yes, I have to daughters and I am a very overly protective law enforcement officer.
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Old 08-18-2015, 02:29 PM   #5
Gallo2011
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Thanks for the advice. I'll start with the plugs and the catalystic converter. And yes, I have to daughters and I am a very overly protective law enforcement officer.
So you had them, but didn't really want to?

Plugs, wires, fuel filter first. Catalytic converter last, as it's more expensive to replace.
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