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My wife's 96 Outback threw code P0304 (Cylinder #4 Misfire) last night after sitting at the airport for 2 days. The light went off by itself today. I ran the code when I got home this afternoon. It has also been throwing code P0420 (Catalyst below efficiency) about once every 4 weeks also after sitting for extended periods.

 

Is this anything to be overly concerned about?

 

Thanks,

 

John

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The cylinder misfire code could be as simple as moisture in the gas - if it reoccurs, more diagnosis is required. The catalyst below eff. code could be the oxy sensor after the cat converter (there is 2 on your car - 1 b4 the cat and 1 after). How many miles on the car and have the oxy sensor(s) ever been replaced?

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The car has 110K and to the best of my knowledge has never had the O2 sensors replaced. She bought the car in 98 with 67k

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Ignore the converter code for now. First you need to determine the misfire code. I would suspect plug wires or a failing valve/guide. It is easiest and cheapest to simply replace #4 plug wire. If you have access to a leak-down tester you should check #4 cylinder.

 

As far as the converter is concerned it is common for failure. Yet you have more pressing concerns with the mis-fire.

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Ordered some new wires and plugs. So far the code has not re-emerged. I put in a bottle of fuel system cleaner as well. I'll swap out and see what happens. Car seems strong, so it may have been an anomoly.

 

Thanks for all the input.

 

John

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