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2016 Subaru WRX
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Discussion Starter · #1 ·
Hey!

TLDR question: After replacing the spark plugs, O2 sensors, air filter, and cleaning the MAF... IS there anything else left to do before replacing the catalytic converter? Would it seriously fail after only 120,000 miles?! Oh, and anyone else had head gasket issues? I might be experiencing those... exhaust smells fruity.



So, I'm going to preface this by saying I am a fairly experienced mechanic (I've even successfully fully rebuilt an automatic transmission for funsies), I just am not very experienced with this specific system. I've never had a cat fail on me before, or even get the codes indicating it is.

I've been getting the P0420 code for the last few months, and every time, I've done the "next repair" to try to avoid replacing the cat.

First, I replaced the spark plugs and cleaned my K&N filter (just the filter, nothing aftermarket)
P0420

Then, I replaced both O2 sensors
P0420

So I cleaned the MAF sensor
P0420
P0420
P0420

It's getting more and more common. The last two iterations were 250 and 350 miles between code clearings, which is making me understandably nervous.

I am finding very conflicting information on catalytic converters. Some say they last 50,000-100,000 miles (Doubtful, my Xterra has over 150,000 miles on it; never had a cat issue)
Some say they only fail if something makes them fail, and that you shouldn't replace them until whatever issue has been addressed.


As far as I know, my engine is running great, accelerates fine, and runs efficiently.

The only two things that MAY be indicating an issue are a burning oil smell (it seems my driver's side valve cover is leaking onto the exhaust pipe, I thought it was the passenger side, but I have since replaced that gasket, and the burning oil continues).

The other thing is one that I'm kinda smacking myself in the head on... I've noticed a few times that my exhaust smells almost fruity... finally did some research...
Do these seriously STILL have head gasket issues?!?! I thought Subaru fixed that like 10 years ago!


Any help would be greatly appreciated.

122,000 miles, M/T. No performance mods, no mapping, all 100% stock.
Bought it second hand after someone had it leased (and apparently had a moron servicing it at the dealership... don't even get me started on what #@!$ I've already fixed...)

Thanks in advance!!!
 

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No, they generally don't have head gasket issues. That doesn't mean a head gasket failure is impossible.

As far as cat life. There is no defined life for one, it depends on the design and the driving style of the owner. It wouldn't surprise me it needs replaced at 100k.

Are you 100% for sure there are no performance modifications?
 

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2016 Subaru WRX
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Discussion Starter · #3 ·
I suppose I would be ignorant to say I know 100% no mods, but there isn't evidence of any.
It went from the leasing dealership to Subaru to be repaired/sold off to the third party dealership I bought it from. I replaced the clutch pretty much immediately, and there was no indication of any kind of performance parts added as I did that repair. It was the stock Exedy clutch.

The air filter was stock (and amazingly clogged, like maybe never changed), and I would assume that would be a first item to change if you were doing any mods.

The average MPG when I got it was 17, so it was driven not too delicately, especially considering how many miles they had on it when they turned it in. (Approx 21k per year. Either tons of city driving, or pushing it hard on the highway to get that low of an average. I'm averaging 28, and I enjoy punching it regularly with my 30 mile commute)

I got the Car Fax before I bought it, and it was at the dealership faithfully every few months for maintenance, up until right before they traded it in, so I would be surprised if they had put any mods on it.

It also has the standard WRX turbo lag, as well as the Suby Stumble, both of which I would think would be modded out.
Exhaust is bone stock, another thing I'd expect to be modded if someone was looking for a few more ponies.

The car is from Arizona, and shows it (the Suby logo on the steering wheel is even slightly melted hah). I suppose now that I'm thinking about it, I know for sure the car has seen more than a few super hot days, and there were at least a few maintenance items ignored, so it's possible that overheating happened once or twice. I've personally never had it come even close though, but my temperatures rarely even hit 100 where I live.

Is there any way to figure out why the cat may have failed without digging too deeply into the engine? I don't want to buy a new one only to have it die due to some other issue I've missed.

Thanks for your reply!
 

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You can temp it. I'm not 100% sure the results you are supposed to see but in general I know that you can check the temperature pre and post cat and that can give you an indication of it's condition. It's been 20 or so years since I was shown that trick but can't remember if temps are supposed to be equal or not.

Can you get a photo of the jpipe? I know the va chassis isn't as easy to photograph as the old ej engines but I want to be sure that the jpipe isn't swapped because that's a common first modification. Many times people will trade in cars and just unmarry the tuner and sell it separately.
 

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Discussion Starter · #5 ·
Here are the pictures.

Aaand... It's the cat.. Temps were roughly 70 degrees colder behind than in front, which is the opposite of what it should be.
327834
327835
327836
 

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BooSTIng
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I don't know a lot about the newer wrx's and the fa20. But I have dealt with a lot of stock Subaru exhaust components before, and that sure looks to be aftermarket.
 

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BooSTIng
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Maybe its my eyes playing tricks on me, but the diameter looks like 3 inch to me. Again, I may be wrong. And the cat before the flange in your first picture looks completely different than the one on the diagram.
 

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BooSTIng
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Actually now that I examine it more, the cat does look the same. The larger part to the side as seen in the diagram is indeed there in the picture. Its just darkened and harder to see. So I stand corrected.
 

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Discussion Starter · #10 ·
Actually now that I examine it more, the cat does look the same. The larger part to the side as seen in the diagram is indeed there in the picture. Its just darkened and harder to see. So I stand corrected.
I was wondering... it's hard to see; it's got some gunk on it.
No issue, I'm legitimately trying to figure out if it's all stock, I appreciate the second set of eyes.
 

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BooSTIng
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I was wondering... it's hard to see; it's got some gunk on it.
No issue, I'm legitimately trying to figure out if it's all stock, I appreciate the second set of eyes.
That's what forums are here for! And it does seem like you may indeed have a clogged cat with that much of a variation in temp before and after the cat.
 

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Discussion Starter · #12 ·
Alright, so similarly related question...
Because I need to replace it...
Any experience with high flow cats? I'm looking at Magnaflow specifically.

I'm not looking for crazy high HP/torque gains, this is my daily driver, and I'm keeping it tame (for now).

Do you get any kind of gain from one of those over an OEM pipe?

Any other brand suggestions for high flow?
To me, if the engine can breathe better, it runs better...
 

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BooSTIng
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I am assuming you mean to buy just a cat, cut out the old/clogged one, and have a new one welded in?

That is a lot of work. A high flow cat itself will do nothing for performance. What I would suggest is replacing the "J" pipe, or more well known as the downpipe, with an aftermarket one with a high flow cat. However, in doing this the car must be tuned. The cobb accessport is a plug and play tuner that will allow you use a off the shelf tune/map for the aftermarket J pipe. This will give you a noticeable power gain, but nothing crazy.

If doing this and tuning the car is not something you want to do right now, then your original idea of just replacing the cat would work, or even buying a used stock J pipe. They can be found pretty easy as that is a common aftermarket piece most people replace.
 

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Discussion Starter · #14 · (Edited)
I think my late night brain was playing tricks hah. What I was looking at (and purchased) was an OEM style mid-pipe with cat, direct bolt on. Not wanting to mess around... I just want my car back :) Thanks again for the help. Now the next bit is to determine if it was age, or something else, that spelled the end of life for my cat.
 

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Discussion Starter · #15 ·
Now I feel dumb. Somehow I didn't click that there are TWO on the car. Now I'm waiting for the front cat to ship.
I was tipped off mainly by the lack of O2 sensors on what I thought was the only catalytic converter... -1 to INT for only ever working on exhaust on cars from the 80s and 90s...
Kinda feel like my WRX just stuck a straw into my wallet...
 

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Discussion Starter · #16 · (Edited)
OK... coming back with yet another question I feel almost ashamed to ask... @WRX-maniac , you mentioned that I would need a tune with a catted downpipe. I bought one because it was the lowest priced direct fit option ($250 for a cat is pretty good), not fully realizing that was what I was buying(the second one, the one I bought today, not the very much OEM rear cat, except for missing the resonator, that I got in the mail a few days ago)

I really really don't want to do a tune. I'm not looking for performance upgrades, and I have an extended engine/transmission warranty on my WRX (the company I work for sells them, and I have had excellent personal experiences with this particular company with other vehicles I own, they really are different than most warranty companies), and an ECU tune will void my warranty, wasting the $1800 I spent on it.

I am also a total weirdo that bought this car for it's fuel economy (I wanted something that was AWD, fun to drive, had good acceleration when I wanted it, and got around 30mpg highway when I wanted that). I am also concerned doing a tune will lower that. I regularly get around 28-31 on the way to work, and usually over 32, sometimes over 35 on the way home from work (rural highways, around 30 miles. It's uphill to work, which is why I get lower on the way there).

I have been searching the internet (including this forum) for the last three or so hours, and I am NOT finding conclusive responses on any forum, website, etc... Everyone who says you "need" a tune is saying that "you won't get performance increases without them" - but no one is really addressing what happens if you DON'T do a tune, especially for the FA20 engine, other than a vague "it may not run as well as you would like" - does that mean lower than stock, or just not a performance gain? More backfires? A piston out the side of the block? A check engine light? (already there!)

Other places have said it's just fine to do it, nothing bad will come of it, you just won't get as much of an HP boost out of it versus if it was tuned.

I live in an area without emissions testing of any kind, so that's really not a concern if that is the main reason.

The main problem here is that I can't find the stock/OEM cat without paying over $1,000 for it. I can find catted downpipes for under $300 pretty easily (the Turbo XS is the one I ordered, again, not realizing what I was buying), and I am concerned buying a used cat will just land me in the same situation I am in currently, and will be a waste of money.

The only other thing I can find is a company which sells through RockAuto who says they will attempt to "prototype" your cat and send you a new one, but it takes a few weeks for the whole process, IF they can actually do it. Otherwise, you're just out the shipping, and back to square one... which doesn't sound great to me.

Sorry for the super long post... I just have seen that this question seems to aggravate those who like tunes on their WRXs, and wanted to explain my "why" behind the question.
 

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If you bought an aftermarket downpipe, which you did, it 100% percent needs to be tuned directly after install. I understand the voided warranty sucks. But buying the cobb accessport and tuning the car will be a ton cheaper than a new engine not covered under warranty when your car goes boom for having mods untuned for.

The fa20 in the wrx has been around for a minute now and cobb knows what they are doing. A stage 2 map from the accessport is a pretty safe tune.
 

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Discussion Starter · #18 ·
If you bought an aftermarket downpipe, which you did, it 100% percent needs to be tuned directly after install. I understand the voided warranty sucks. But buying the cobb accessport and tuning the car will be a ton cheaper than a new engine not covered under warranty when your car goes boom for having mods untuned for.

The fa20 in the wrx has been around for a minute now and cobb knows what they are doing. A stage 2 map from the accessport is a pretty safe tune.
Thank you.

So actual engine damage is a strong potential. Well, I'll be calling my warranty company tomorrow and seeing about getting at least a partial refund. I talked to my wife about it all today, and she's actually pretty sold on the AP tune, since it's so hard to buy OEM style aftermarket parts for our awesome cars.
I was able to cancel the downpipe order, but depending on how the conversation with Route66 (my warranty company) goes, I may be going for a stage 2 tune after all.

I like the idea of smoother acceleration and better pedal response, along with other benefits more control over the ECU will bring, and who knows... Maybe I'll start down the modding rabbit hole and end up at 400whp (probably not lol, but we will see).

Hopefully I can continue to get good MPG with the tune and new parts... Provided I can keep my right foot off the gas hah.

Thanks again!
 

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Thank you.

So actual engine damage is a strong potential. Well, I'll be calling my warranty company tomorrow and seeing about getting at least a partial refund. I talked to my wife about it all today, and she's actually pretty sold on the AP tune, since it's so hard to buy OEM style aftermarket parts for our awesome cars.
I was able to cancel the downpipe order, but depending on how the conversation with Route66 (my warranty company) goes, I may be going for a stage 2 tune after all.

I like the idea of smoother acceleration and better pedal response, along with other benefits more control over the ECU will bring, and who knows... Maybe I'll start down the modding rabbit hole and end up at 400whp (probably not lol, but we will see).

Hopefully I can continue to get good MPG with the tune and new parts... Provided I can keep my right foot off the gas hah.

Thanks again!
Oem replacements are the most abundant on the market, by a absolutely mamoth proportion.
 

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Discussion Starter · #20 ·
Oem replacements are the most abundant on the market, by a absolutely mamoth proportion.
Really? I've been having the opposite experience, at least for what I've needed to replace so far.

I guess I technically CAN buy a catalytic converter that is OEM fairly easily, but it's more cost effective to buy a downpipe + cat & do a tune. ($1200+ for one, not including shipping. Dealers seem to be the only ones who carry that particular part)



What are some good websites?

Rockauto is out of stock on like everything 15+ WRX, and that is who I've faithfully used for 10+ years.
 
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