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2004 Forester XT 5MT
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Discussion Starter #1
Long time stalker first time poster.

I've got a stock 04 FXT MT with a 154k miles. It recently threw the P0420 engine code. I took it to a local Meineke to see what was up. They checked out the cats and 02 sensors and found the front cat is dead and the rear 02 sensor is heat seized in so they couldn't check it out but given what their readings were he's guessing that cat is likely at 40%. At 15 and a half years old and over 150k not surprised with the cats going out to pasture. My fuel economy has been going down a couple mpg (I'm obsessive enough I track it in Fuel Log on my phone).

The problem:
He can't find a replacement front cat. Of the six suppliers he called none of them have an OEM front cat. Magnaflow has it listed as "coming soon" but with them saying it's fitment is for the 04-05' XTs and no other makes or models I can read between the lines and hazard a guess on how soon "soon" will be. He even reached out to one of the local Subaru Dealers and they quoted him like 4 grand. I live in North Carolina outside Raleigh so I'll have to pass emissions inspections yearly. If I just went with a catted downpipe from Cobb or TurboXS then I'd be looking at needing to tune it etc to pass emissions, right? I also reached out to my old mechanic outside Chicago and she said, they've had "crap luck" (her exact words) with basically any original equipment replacement cats on this age of Subaru other than Magnaflow.


My question:
How much hassle is it to actually tune the exhaust to pass emissions. I'm not looking to cheat the system I'd keep a front and rear cat. I'm assuming I could mate either a Cobb or TurboXS catted down pipe to say a Magnaflow rear cat and be okay. Would I need different 02 sensors, are there other parts I'd need to make it work? If the cost of the aftermarket equipment and tuning is going to get up into what Subaru wants for the job then I'd likely just have Subaru parts put on and sell my first born. I'm starting to feel even though I love the FXT and it's been a great daily driver for popping around town it might be easier to sell it to someone whose looking for one to mod or doesn't have the emissions inspections to deal with. I'm both mechanically and electronically savvy so I'm not too worried about getting in over my head. I'm just facing a scenario I've never dealt with before, so really looking for advice and guidance.

Thanks in advance!
 

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2018 X3 M40i / 2016 X3 xDrive35i
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1,622 Posts
Did they replace the front o2 sensor? The P0420 is usally resolved with the upstream sensor replaced.

As far as downpipes, used OEM downpipes are all over the place and cheap. I bought one from an 07 STI take off that was removed before the donor car had its first oil changed. I bought it and a new rear o2 sensor for around 150 for both with gaskets.

Your mechanics are making this way harder than it needs to be.

Check out local subaru facebook groups, auto recyclers, craigslist, etc.

But before you do that replace the front o2 sensor.
 

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Registered
2004 Forester XT 5MT
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2 Posts
Discussion Starter #3
Did they replace the front o2 sensor? The P0420 is usally resolved with the upstream sensor replaced.

As far as downpipes, used OEM downpipes are all over the place and cheap. I bought one from an 07 STI take off that was removed before the donor car had its first oil changed. I bought it and a new rear o2 sensor for around 150 for both with gaskets.

Your mechanics are making this way harder than it needs to be.

Check out local subaru facebook groups, auto recyclers, craigslist, etc.

But before you do that replace the front o2 sensor.
Interesting, good to know about finding a used downpipe.

He didn't replace the front sensor. I'll talk to him about that.
 

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2004 FXT / 2020 Outback Onyx XT
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1,663 Posts
I’ve had a p420 off and on and have passed state inspection when it was off after clearing the code.
 
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