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02 Subaru Forester Catalytic Converter Issues?

  1. MAKE: Subaru
    MODEL: Forester
    YEAR: 2002
    MILES: 160,000
    ENGINE: 4-cyl 2.2

    Trouble Code: P0420

    Losing approximately 1 quart of oil/month (every 2k miles)
    No driveway stains - confident we're not leaking much if any

    Some dark exhaust staining on the tailpipe exit

    KICKER: When I drive the car up to about 3,000 feet elevation, the trouble code goes away and the car maybe even seems less sluggish (could be my imagination on the performance)

    I don't know where to go with this other than a CC problem. Any ideas?

  2. sure its a 2.2L? maybe a 2.5L?

    ANYWAY that's a lot of oil consumption.....you might look at that- 2002 I think is before the problematic ring issue.
    If applicable the turbo when the seals go they consume big time- How do plugs look? do not use a K&N type filter. Use correct T'stat. Check PVC.
    you would want to use scanner and check FT's, MAP and ECT - ALSO LOOK AT THE ACTUAL O2 VOLTAGES...
    maybe do an exhaust system back pressure test- would look at that sluggish issue...
  3. No turbo on this one.
    Plugs are clean.
    I'll put the scanner on it and report back.
  4. Sadly, with a high oil consumption like this you may have clogged the cat. But, black smoke usually means the car is leaning out due to a possible exhaust leak and the ECM is enriching, hence the black smoke.

    I see only a 2.5l non turbo. No 2.2l available for this car. Turbo for this model started in 2004 and still in 2.5l.

    Are you having any idle issues or stalling?

    Do you have any exhaust leaks?

    Do you know how to do a back pressure test as Kev2 suggested to confirm cat blockage?

    Are there any other code present?

    When you clear code/s, is it only the P0420 that comes back?

    I do not see any TSB's of note for this code on this model.

    Check, as said before, for any leaks in exhaust system.

    Do you know what fuel trims are? And if so, do you have a way to check them?


  5. Yep. 2.5 and non-turbo. There was a TSB about heads, head gaskets, if I remember. Repair was done by a dealer just before the time or miles ran out, around 80,000-Miles again if I remember. Just seems to me that things like the Valve Guide Seals should be "low mileage" at least thinking they were changed on the TSB repair.
    Have any Sensors been replaced? Knock Sensor, O2 Sensor(s)? Others? I remember a misfire on one cylinder, burned coil terminal and associated cable terminal. Changed Coil and Ignition Cables. And Plugs... All looked alike and none oily.
    What was the Ring Issue about?
  6. check the PCV and hose for evidence of excess oil.
    As for the ring issue -Try google "Subaru ring problem" that will get you some info and years affected.
    for back pressure - there is a gauge that is swapped into an o2 sensor for testing OR a vacuum gauge can be used- maybe available as rentals or loaners at parts storws.
  7. Doesn't seem it's new enough for the ring problems described in the gOOgle search, Lawsuit, TSB's etc. The oil consumption's a relatively recent development with this 2002 Forester. Seems to me that the "boxer" style engine layout makes it easier for crankcase oil to get to the pistons. Anyhow, can it burn that much oil and not have it show on the plugs? I can see how the converter could burn the oil so completely that the exhaust didn't smoke, but the burning oil not show on the plugs???
  8. Yes, an engine can gobble oil and not have it show on the plugs or affect emissions. The S-series Saturns that I love so much are notorious for using lots of oil, but there are no problems from that unless you don't check the oil level regularly and run the engine without lube.. Subaru is not the only flat-opposed engine, don't blame high oil use on that. Ha, at one time there was even BS about pistons wearing rapidly with anything other than vertical cylinders!
  9. Yes it is the 2.5L sorry for the typo.

    I put the scanner on looking for the O2 sensor data etc. and could only get one sensor to report. I have Bluetooth OBDII with Torque lite. Anyone know if the full version of Torque will let me see data on all sensors or is this an issue with the car?
    Also, a particularly strange phenomenon is that after I clear the code, the car usually stalls on the next startup, but at no other time.
    I think I could perform the back pressure test but I don't have the vacuum gage. I'll see if the local parts place lends them out.
    We have replaced O2 sensors at various points to get it to pass emissions but not the knock sensor.

    Thanks all,
  10. stall after clearing code- I would not worry if it corrects on second start- erasing a code dumps the code and much data including - so called adaptive's, learned settings, monitors etc...
    You mention 3000 feet that's rare - Colorado? You are not using that 83 octane -
    do not give up on her without testing at least the fast inexpensive testing.
    look at the PCV system....noticeable wet with oil in tubing?
    Again I ask is it reaching temp what is ECT?
    which sensor reported and what was voltage?
    why are you now questioning KS knock sensor?

    you need to talk with scanner manufacturer tech support - what each brand will do is always different- one question you should ask will this scanner read ALL codes the manufacturer specific?
  11. If you have the OBD2 bluetooth dongle, scrap that torque lite app, the torque pro is no really any better a thing for your I phone app.

    Go for something like proscan or something similar. What is your OS? Windows version #???

    Is your dongle a canadian based ELM device? It was originally a canadian based company but was soon copied by the chinese which swamped the market. So if buying those inferior elm's, highly suggest to buy a few. A 10-20$ a pop, not a huge loss if one does not work out of the box. Also, make sure you have the 5.5 proscan version and elm 1.4 dongle version. From what I gather, the 2.2 version is for the android app shyte and I have no use for that. I use strictly laptop or PC based.

    You probably own a laptop, right?

    Try this link for free software. Many of them work great with a proper setup. A phone is still just a phone and cannot have the processing power of a good laptop and high baud rates needed to see live data switching.


    You need something that will read PID data. Torque lite and the pro versions are still just glorified code readers and a app gadget to see what fuel mileage you are getting and some fake dyno results etc. Don't get me wrong, for a free app, it can help. But not for in depth diagnostics.

    I am not allowed to give cracked software links here, so check out on your own. They are readily available and will work with a good interface. Some of the software state they will only work in older versions of windows. They can be run in compatibility mode.

    Linux is more stable across the board, but restricted in software abundance compared to windows OS's.
  12. So, from this I am gathering no other codes are present when check light comes back. Am I correct in this assumption?

    Screenshot (520).png Screenshot (521).png
  13. Especially check step # 2 of the above flow chart. I have seen a lot of guy's just say, ahh, it can't just be that!!


    That black smoke is TELLING you something!! That is why I asked for fuel trims, which a torque app will not give you.

    Raw fuel is being dumped in there for a reason and the cat could be cooked already. Most likely already a done deal. The coating of the honeycombs could be already beyond its capability to perform. I check this out often when I get a dreaded P0420 code with a laser temp gauge.

    How is acceleration and engine performance? Is it sluggish. If so, does it improve with the pre o2 sensors removed? It may sound like a nascar, but subbie's are loud off the lot anyway. That's why I don't like them. Those cars sound like a sick cow farting when they drive away. But they do make for fun driving. :p
  14. why are you now questioning KS knock sensor?
    @kev2, I think he mentioned this cuz JD asked him this above question.
  15. Hmm.... Fuel... Doesn't run all that badly, right? But poor gas mileage for a car that size, way lower than three other 2.5L Subies that've been in the family. Fuel trim isn't a term I understand, but... Raw gas washing oil off the cylinder walls and out the exhaust?
  16. @jd, fuel trims are a neat thing to look at for this type of code.

    Since you wrote that it is a term you don't understand. I thought maybe you would like to know what that term means.

    Fuel trims are a measurement that the ECM needs to lean out or the enrichment of the fuel to air ratio to maintain a balance. I think maybe this video will do more justice than me and my sloppy wording.

  17. "Fuel trims" are how much the PCM modifies the injector pulses, either rich or lean, from the programmed values. The PCM is altering fueling from the programmed value in response to what the upstream O2 sensor is reporting on how the air-fuel mixture (AFR) has burned. That's why getting live-data readings on the O2 sensors is so important here, we are just guessing without that info.

    There are both "long-term" and "short-term" fuel trims. Long-term account for gradual changes in things, like a fuel-pressure regulator slowly drifting with age, or compression changing due to ring wear or carbon build-up in the cylinder. Short-term is in response to intermittent issues, like a vacuum leak in a hose that only occurs when the engine moves to a certain position. I'm kind of generalizing, but I hope you get the idea...

    Excess fuel can wash oil off the cylinder walls, but generally is not much of an issue if the engine will run, even pretty rich. The excess fuel is mostly vaporized and little really gets onto the oiled surfaces to dilute the oil film. Especially since most of the oil film is below the piston rings, not very exposed to the air-fuel mixture, whether it is too-rich or not.

    Edit: added not!
  18. Yeah, what Bill said. He has a better way of saying things than I do.

    I will repeat myself, BLACK smoke is raw un-burned fuel. When a cat goes south, the chemical reaction can no longer get hot enough to burn the NOX's and such. Hence the in-efficiency of the cat/s.

    In a region like mine, this would be a moot issue, we don't have emission testing up here.

    When the programmed algorythm is not seen and under or over valued, a P0420 code will set and this is basically the ECM/PCM asking(begging) you to check the exhaust system in its entirety. Most often a cooked cat.

    Now, the question is why did it get cooked??

    That is the 800$ new cat question.

    So this is why fuel trim and o2 switching readings are so important.

    Who wants to spend so much money on a cat when possibly it is only a 2$ gasket leak?
  19. I downloaded the OBD Auto Doctor software and got the trial version going to test. I have it connected to the vehiclee, but the Oxygen Sensor Monitors tab says that it is "Not supported by the Electronic Control Unit". It does have fuel trims, but they're not available in the trial. I'm trying to decide if it will be worth it to pay the $50 for the software without the O2 sensor info.
    I'm going to check the PCV and exhaust system today - will report back.

  20. MikeD, you are a trooper. Keep at it. I can't wait to see your result after exhaust inspection.

  21. Thanks nickb2! I'm a total newb but I'm going to keep on going at it. I appreciate the support from everyone here.
    Rear of the car is to the left. Catalytic converter on the right of the pic.

    Also found an oil leak in vicinity of the oil filter. The oil filter let me tighten it by hand about 1/4 turn. Looks like the oil loss is unrelated to the P0420 code.

  22. Update on that little Subaru Forester Biter: This is the one I just spent hours on with Headlight Wiring...

    It had been running "OK", about Average, Uses more gas than it should (did that on my 8,000 mile trip back from Alaska in 2011, too, but no Check Engine or Oil Loss), black sooty tailpipe end.

    Till last Saturday. Started up extremely rough. Check Engine Light FLASHING. Overheated! Engine Hot, Radiator Cool, Coolant FULL. MikeD took it to a shop. Shop's a good one, but couldn't duplicate the condition. Wrote an estimate for miscellaneous fluid leaks and power steering rack problems bu nothing addressed what happened Saturday. Ran OK to and from the Shop.

    Sure seems like a Sticking Thermostat. Replaced Thermostat and made up the little bit of coolant it lost. Ran OK. Saw evidence of the oil filter leak MikeD noted above. Also noticed oil was full, which it's rarely been.

    Till Tuesday. I'd warmed it up, checked for leaks, all OK. Pulled out into the neighborhood, Bad Shakes, Flashing CEL... Mike told me I'm not allowed to drive it any more and we parked it. I hope he'll take it back to the shop.

    We were swapping cars. Leaving our Ford Aerostar (1997 with 75000 miles) and taking the Forester the 700+ miles back home. We made the trip yesterday in a 2017 Hyundai Accent rented from Budget.

    Shop tested some engine management/emissions items, said both O2 Sensors were Good.

    I doubt I'll ever see that Forester again...
  23. Wow, update from 2016. Glad you fixed it??
  24. BTW, whatever happened to MikeD? Still around or dead?
  25. My daughter's husband. Alive and well. Hasn't changed the CAT or done much beside tighten the filter. Planning to sell the Forester.
  26. Good, cuz for the few times he came here to BAT, I found he was solid. He must be cuz he is family now for you. In french we say "beau fiston" slang for son in law, I think. The Innu use a different term. "Innuatsh" The innu language is quite complete when you start to listen.

    I mostly will miss the elders and there easy way of just being/existing. Very wise ppl. Hats off to them for sure.
  27. Solid Indeed, My Friend! We're blessed that our daughters have married stand-up men, and that they freely include us in their lives.
  28. It's been awhile, but MikeD started the Suby up today with one of our cheesy OBD senders and TorqueLite. It shivered and shook like I'd experienced, and threw Codes P301 and P302, Misfire #1 and Misfire #2.

    I think that ignition uses "waste spark" where 1 and 2 are actually connected to one coil in the pack, and 3 and 4 are connected to the other. When 1 is on power stroke it gets spark but so does 2 even though not on power stroke, from one of the only two coils in a four-cylinder pack. Firing order is 1-3-2-4 so no spark to 1 and 2 would produce an engine running on Miss 1==>Fire 3==>Miss 2==>Fire 4. A relatively smooth running two-banger like an ONAN welder engine, just with no power.

    I also found that only one timing belt drives cams, oil pump, and water pump plus a few idlers. That tells me the overheat we had must have been a sticking thermostat. That, since coolant stayed full, none was lost, and overheat never came back.

    I conveyed all this to MikeD, but whatcha'all think?
  29. If no presence of overheating, a t belt kit is fine for these horizontal engines. The heads on those are very durable.
  30. If your getting repeat codes as stated before, after repair, then you need to investigate the wiring
  31. While your at it, a t stat is always a good idea since there very inexpensive.
  32. It overheated that once, and I thought it could be related to the missing condition that MikeD didn't get codes for yesterday. But yes, I already changed the T'Stat. It ran normally. Then next day, the apparent loss (intermittent of course!) of those two cylinders flagged by the codes. It's like you and Quebec, about 750 miles north of me now.

    I forget how the Coil Pack connects. Could be a very good step, to check that connector!
  33. :fixed:SITREP 33 and Final. MikeD replaced the coil, Suby ran OK again, listed on Craig's and and sold on 20JUN17. Editorial remark: I'll miss that car! Probably driven it 10,000 miles myself over the years. CASE CLOSED:fixed: