In the spirit of a horribly annoying, current meme subject going around, I am once again asking for your Subaru troubleshooting advice. Haha. Picked up a Forester for the wife last summer. 160k-ish, na/5spd. Nothing special, just a decent daily. Had a misfire and sluggish low end when we got it but that was fixed with a tune-up (plugs, wires, coil). Found carbon tracking on the plug that had the misfire. Ran considerably better afterwards. Wife says she's had a P0420 sporadically a while ago but nothing recent. Now she's complaining about a rotten egg smell when she gets out of it. This is leading me to believe the cat(s) are bad/clogged? How does one tell without just replacing them? If they need replacing, I'd be more inclined to go catless and cheat the system with a resistor (is this possible on an na car?) due to how obnoxious cat prices are going for currently. One other thing worth noting, is we both start our cars and let them warm up for a minute or two in the garage in the morning. My car is totally catless (03 WRX) and her car is all stock. I swear the exhaust coming from hers is way more "potent" than mine. I kinda dig the almost "sweet" smell of catless premium burning. Hers just makes your eyes and nose hurt. Haha. Would this also be "bad" cat related? Thanks for any assistance!
In my experience, sulphur odors are more likely to be when the car is running rich and the cats are working overtime converting the unburnt fuel. This will kill the cats given time, but replacing them is generally not the main fix. It's likely the O2 sensor is giving bad readings causing the car to run rich. If this was a Nissan I'd suggest that there was a bad injector as well, but I dunno about the Subaru failure modes for injectors.
While probably expensive, a new OEM O2 sensor is probably considerably cheaper than new cats. I feel like it could easily be running rich due to the fuel smell in the exhaust.
If the O2 sensor is the same as a 2002 wrx I have a spare I could part with. I had replaced mine thinking it was bad and then shortly after found out my injector seals turned to plastic.
To check cats, check temp pre and post on the exhaust. If its "dramatically" different, then there is a restriction.P0420 can be caused by lots of things, bad cats, o2 going out, leaky injector, plugs / coil, burning oil, blah blah blah. If the car is due for some basic maintenance, it probably wouldn't hurt to check off some of the cheaper items on the list. If it needs cats, you can get aftermarket exhaust parts pretty reasonably actually.
Is there a set price point needed to achieve decent functionality? I've looked on Rock Auto and they range from roughly $200-$700+... Reason I bring this thread back up is we've still got an issue with this thing. Still has an intermittent P0420 code and that's after I replaced the front O2 sensor (don't even remember when exactly, but it was sometime this past summer. Monday night my wife filled it up before coming home. I took it to St Paul that night with a stop to Robbinsdale both on the way and back home (had to pick up/drop off a friend). I put in almost exactly 100 miles that night and the thing hauled through half a tank of gas in the process. Something is definitely wrong... I'm gonna have to locate an infrared thermometer to check temps, and also found that you can monitor O2 sensor voltages front and back as well. Are there any other surefire ways to troubleshoot these things? In most cases I would just chop these damn things apart and replace the cats with pipe, but I don't really have unlimited time right now and this unfortunately is our primary vehicle currently given that it's AWD with snow tires. That said, I'm probably looking at popping a cat in and out in hopes of saving time at least, and hopefully not going broke in the process.
I'm gonna go back to what I said about injectors. If you had a bad cat, it could cause excess fuel consumption if it was clogged, but it would combine with a huge loss of power. I think you've got a stuck injector that's dumping way too much fuel.
Vector has a point here. Depending on mileage, maybe do some general maintenance/inspection on the car before condemning the exhaust(Check plugs, wire, coil, check for leaky valve cover gaskets putting oil in the spark plug hole, air filter, clean the maf, etc). If you have a injector thats sticking you may be able to find it by the plugs, and doing an oil sample to check for excess fuel in the oil. Clogged cats primarily have low power symptoms, easiest way to diag is FLIR or laser temp gun(many of these are very inaccurate) to see temp differential pre/mid/post cat.
Maybe you can learn something by connecting the green test connectors and watching/listening to the injectors cycling?
When I worked at Subaru, the majority of the cars that we put aftermarket cats on came back in a month or so with the P0420 back and ended up with OEM. We had better luck with the ones listed legal for sale in California. I agree that that is likely not the issue. I would start with watching live data fuel trims and AF/O2 signals. If the short term trim is all over the place, and/or the long term is trending more than a few percent either way, you've likely got a fuel issue. Stuck or leaking injector, or leaking fuel pressure regulator. If you're getting way too much fuel, the cat will be glowing red after driving it. What brand coil/plugs/wires did you use?
That sounds good. I don't think my scan tool is good enough to do fuel trim stuff, unfortunately. I'll have to pop the hood tonight and check the wires. I wanna say the plugs were NGK, of whatever variety was stock. If it ends up being injector related, is there a specific brand I should shoot for? Thanks everyone for the suggestions!
Bluetooth dongle to tether to a smartphone is only about $15. I use a combination of "ActiveOBD" and "Piston" Android apps (both free). You are going to need to look at live data to properly diagnose this. Maybe you can find a shop to test/clean the injectors? I know one of the local garages up here can do that, there must be something down there. Pull the vacuum hose off the regulator after running and see if there's fuel in it. Was there any oil on the spark plug boots? It's not uncommon for the tube seals to leak on these. Usually causes a misfire, but maybe you've caught it early. P0420 diagnostic process is considerable.....
