2001 Subaru Forester -- make an expensive repair, or pack it in?

If it were mine, I loved the car, and I could afford to do the repair, I'd repair it. Not from financial analysis or any of that logical stuff, but because a car you like is worth keeping. Maybe (probably [ok, definitely]) I'm pickier than most about my cars, but almost every time I've replaced a car I loved, I've regretted it (and that's when the replacements were ostensibly big upgrades). You don't say how much you like it, and hopefully you're not as crazy as I am, but that's what I'd do.

It is really helpful if you state the codes you got. I believe when you had the two-cylinders misfire you should have been getting P030x and P030(x+1). If it is P030x and P030(x+2) it is indicative of a head gasket failing. This could make a short-term problem with the cat, but given the quick resolution in the linked thread, everything around 18 December, I doubt it. What makes you think the cat is the problem, especially since the new cat is only two years old? If you have the codes, please so state. Alternators and cats are orthogonal (neither has anything to do with the other. You were unlucky with your alternator. None of my Subarus has had that problem.) Fear not, if the car is as described I will buy it from you. Foresters of that era are very solid machines and at 135k for $4k I'll chance the head gasket possibility.

Random data point, but my dad has this generation of forester and put another 100k miles on it compared to yours. I drive it once or twice a week, it still runs pretty well. The head gasket is FINALLY failing again(it was done right smack dab at 100k and a tiny bit of change) but it has been for... a year now, with no real ill effects or it even throwing a code. It's survived almost entirely on cheap repairs. A few expensive things have been perpetually put off for 50-70k miles with no real serious problems arising from it(the rear diff started having a very slow leak around 150). The biggest recurring problems were oxygen sensors until the parts got better or... something, and they stopped failing. My dad is planning on driving it until it fails in some way that costs more than 1k to fix. That's been the plan for well, the past 5 years at least. We both haul around heavy stuff in it and use it as a cargo hauler in general. It's the most bulletproof car any of us have owned. That smell you described has happened for years, and it's on ours it was a tiny oil leak onto the exhaust manifold/cat area. Our solution was to always set the fan to recirculate and crack the windows if the windshield gets foggy.(seriously) A similarly trusted shop said "well you could do x and y and z and it would stop it, or just ignore it and check the oil occasionally". I'm on board with the downstream cheap parts theory. When it's seriously acted up like this, it was just a cheap sensor or two. It's thrown this code, and changing the sensor got rid of the code returning after we'd clear it and it didn't come back. It did eat sensors every year or two for well... a lot of the late 2000s.

Having one, much less two, catalytic converters fail like that is intensely suspicious. I think there's some underlying problem at work that was not solved originally. Whether it was related to the issue in your previous AskMe, it's hard to say. I would get a second opinion, no matter how much you trust the garage. There's just too much money at stake, and even if the shop isn't consciously ripping you off, it doesn't seem like they necessarily know what the issue is, either. Cars do not just "lose their mind" temporarily. That's somebody saying "I have no clue" without coming right out about the fact that they have no clue. Anyway, I'd probably work my way through various sensors before replacing the converter, and do it only as a last resort and only if you are really sure it's dead. (And unless you are 100% sure you've fixed the underlying issue I'd certainly not stick a new one in there, I'd be putting a junkyard part in from a wrecked vehicle obtained from your friendly local pick-n-pull for sure. And then only to get it through emissions testing.) On very little basis at all, one thing I'd check, or have someone check for you, is the fuel system. It is possible in some cars for a failing or otherwise underperforming fuel pump, or clogged fuel filter, or any number of other things on that side of the engine, to starve the engine, causing it to run lean, and that this can damage a converter over time. I've never actually had it happen to me personally, but it's certainly theoretically possible and depending on the design of the car can sometimes not trigger the idiot light until it's too late. Anyway, just something to consider in addition to the "running rich" failure scenario. Whether this is something you want to deal with vs. sell, I can't really tell you. I wouldn't fault you if you did some sensor swapping, and if that didn't correct the problem you just took the car down to CarMax and got rid of it and got a different used one, taking a bet that you won't get another one with the same problem. The buy/sell spread on a similar used car might not be that much higher than what you're looking at for the converter repair. And going through a converter every two years is not something I'd tolerate.

P0420 is a crazy common code across almost all manufacturers, but especially Japanese car makers for some reason. Your mechanic is simply telling you what the reference book says the problem is. He doesn't actually know with any certainty. If you replaced the cat two years ago, the problem is pretty likely not the cat. I'm betting you didn't need to replace the cat back then, either. The P0420 code is based on what one of the O2 sensors in the exhaust line is telling the computer, vs. what the computer thinks it should be expecting from that sensor. If things don't match, the computer throws the P0420 error. I had a 2001 Nissan Maxima that had what I called an eternal check engine light for exactly the same code. It started throwing the code within the first year after I bought it new. Since I live in a state without car inspection, I opted to let it go. It never affected performance. A lot of people report that installing a spacer where the particular O2 sensor mounts, in order to move the sensor out of the exhaust stream, solves the issue. I'd do something like that before I spent money for a new cat. You have relatively low miles on the car. And Subarus are mode for the long-haul. Keep it.

2 years is really short for a cat converter. Did you install an after market one or an OEM last time? Regardless, I would keep her, but I drive my vehicles into the ground. Got a truck with 135,000 on it and I am expecting at least 200,000. For me, it is not so much what it is worth, as it is what is the replacement cost and why get rid of something that still works and has value. You can buy a new car in a few days if this and your toyota were to crap out. I would take the risk of having to rent a car for a week. YMMV (pun intended).

Answers to a few questions raised: Current code is P0420. (I'm not sure how they know the problem is the catalytic converter and not the O2 sensor. Both are new as of January 2013.) Codes for the two cylinders were P0303 and P0304, so x and x+1 as you say. I've been using this garage for 10 years and trust them. The catalytic converter they installed in January 2013 was original from the manufacturer, not aftermarket.

The cylinder failure is a very plausible explanation for a catalytic converter problem especially since, when the cylinders were acting up and you "parked at my son's school, [you] could smell a kind of burned rubber smell in the back of the car." I would guess that enough unburned fuel was dumped into the catalytic converter then that it overheated to the point that it cooked a rubber vibration damper that is often a component of exhaust system mounts, and so much heat can seriously compromise a catalytic converter.

I'm trying to understand what diagnosis leads you to believe that you need a new catalytic converter. Is your check engine light on? Does the car run poorly? It's really difficult to believe that an OEM converter would last 12k miles. My answer to your first question is that it's doubtful there's some other serious problem contributing to the early failure. Realizing you've been with the same mechanic for a while, I'd still strongly suggest getting a second opinion. If the location on your profile is accurate, there should be at least one other Subaru specialist shop in your area. Is it time to buy a new car? That's bit more complicated to answer. I've owned two Subarus in the past, and have replaced them at about the same mileage where yours is at. The running gear (AWD and transmission) are pretty bullet-proof, so you shouldn't have many issues there. On the other hand, many Subarus tend to develop leaky head gaskets, and oil consumption goes up as they get older. But since you only put 6k miles on a year, you might well get a few more good years out of your car. Have you considered what you would replace your car with? I no longer drive a Subaru for a few reasons: Their cars, especially the Forester, have become bloated and more expensive over time. They have replaced automatic transmissions with CVT, which I'm just not crazy about. And finally, Subaru's interior designs haven't quite kept up with the times, if that sort of thing is important to you.