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I got this car for free in May, from a friend who lost the timing belt at about 60 mph. He didn't want to pay for the repairs, so I got it. I pulled the head, all 4 exhaust valves were bent. Had the head rebuilt, new exhaust valves, intake valves cleaned up, new seals etc. Anyway, put it back together and it runs like a top. Car has 84000 miles. Anyway, about 70 miles into the rebuild, check engine light came on, with a DTC of P0133. Searching these forums, I found it was either my upstream O2 sensor, or a leak in the flex pipe. I crawled underneath the car and did not readily see any cracks in pipe. So I replaced the sensor, and after 70 more miles or so, the light came back on. Same (and only the one) code, so I reset the light and drove it some more. Anyway, this cycle went on, for close to 800 miles, resetting the light every 70 miles or so, until I finally got to borrow a lift and get under the car to properly inspect the exhaust! Well, sure enough (as the TSB I read on this forum stated) the flex pipe was cracked on top, making the car throw the P0133 code. So I ordered a new flex pipe, installed it, no leaks or anything. Cleared the codes, and thought that was the end of it. But about 30 miles after that fix, my check engine light again came on, this time throwing a P0422 code, saying the catalytic converter isn't working efficiently. I re set the code, and it reappeared about 25 miles later, did the same again and this time it took about 65 miles to reappear. I drove around, with my scanner hooked up and looked at live date from both the upstream (new) O2 sensor and the downstream (original) O2 sensor. The upstream would switch values, anywhere from .035V to .740V, and the downstream would be anywhere from .070V to .750V. I read somewhere on this forum that the upstream should read anywhere from 0-1 volt, and the downstream should be .4-.6 volts. So could the problem be the downstream sensor? Or is it just telling me the oxygen content is way off, and the cat isn't doing it's job? I'm not one to throw parts at a vehicle, I want a correct diagnosis. I've read elsewhere on this forum that people have changed the cat and both O2 sensors, and continue to get the P0422 code.

Any help greatly appreciated! Thanx!
Steve
 

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Discussion Starter #2 (Edited)
update

I see there are quite a few views of this thread, but no replies, so thought I'd update, not only to keep this thread alive, but to help others that may have the same problem.

I certainly appreciate all the info I gathered on this site concerning the P0133 code I was getting, then replacing the leaking flex pipe as this was the fix (as the TSB stated) I needed to clear that code. I feel the P0422 code cropped up after the fix, as the integrity of pipe was compromised before with the leak between the two O2 sensors, and now, closed up, the second O2 sensor got a more accurate reading, and threw the code. After all, that's pretty much the function of the second sensor. But I'm not convinced that sensor is good, and I don't throw parts and money at vehicles, until I'm sure of the problem!

So I plan to swap the second sensor with a known good one, and re measure. If it's the same story, by reading the voltages and seeing if the CEL lights, I'll probably go ahead and change the cat. I don't think the problem is a badly plugged cat, as the car seems to run pretty smoothly..however, I do have a bit of a stutter sometimes when accelerating, so it may be part of the problem. It may be the cat has broken down and no longer does it's job (my best guess). If that's the case, there's no emission tests here, and I could just leave the CEL on, but I can't stand anything not working like it should! I won't stand for a dome light not functioning, or a burnt out instrument panel light!!

Anyway, if any others are having this problem, I will report my progress in the near future in hopes that it helps any others having similar problems.
 

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telling him to see a 'pro' is a complete waste of his time and everyone else's. furthermore, his codes aren't the charcoal canister. try harder.

i'll take a look at this for you steveinyak, but it'll have to wait till wendsday...i'm on night shifts at the moment so i'm a little whacked.
 

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a day late, but as promised here's some thoughts. unfortunately, that's about all i can offer. i find that sometimes random thoughts lead me to the answer though.

for starters let's get to the basics - i'd check the flex pipe and rest of the exhaust again. once done that, i'd check it again. with the engine running, you can usually hear or even see an exhaust leak. just make sure it's tight before you go any further.

if my memory is right there is a TSB to have the ECU reprogrammed for ....you guessed it....faulty O2 sensor codes. if unsure if ECU is up to date, wouldn't hurt to check that. my local dealer checked for free couple years ago since its a TSB and i was having the o2 sensor code.

cat isn't cheap....really not cheap in these cars. if it comes to it, i see 2 possible answers:

1. find a shop that has an exhaust test tool, **** even talk to a shop that does emissions testing. if the cat has failed, would be nice to confirm by getting a sniffer on the exhaust. if its fine, replace o2 sensor. if its still throwing code, forget about it.

2. hate to say it, but replacing the o2 sensor is an option. i'd recommend disconnecting battery to clear ECU first. this can solve the problem on rare occasions. very rare....you'd need to drive for a bit to see if it comes back.

hope that gives you a few ideas at least. let me know how it goes.
 

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Discussion Starter #5
Thanx Zero, I certainly appreciate your response! I have gone over the exhaust again and again after replacing the flex pipe, and like I said, the TSB concerning the P0133 code was right on. That code disappeared. I think the P0422 appeared because the second O2 sensor was able to measure better when the exhaust system no longer leaked. I did change the second O2 sensor with a known good sensor with the same results. After talking to cat "experts" it makes sense the cat went bad after the previous owners continued to drive the vehicle with a rotted flex pipe, with a check engine light (they admitted to this) as the computer would read this as a lean condition and run rich. Extra fuel over time will ruin a cat. So I have ordered one (not a bad price really, for what I see some cats go for) and I will report back when I change it.

As for taking it to a shop, or such, it's not an option for me. I live in a bush Alaska village with no roads in. All vehicles are barged in, and shipping one out to have it serviced costs as much as the repairs, or sometimes, the vehicle. That's how I became a mechanic 40 years ago, not only for the love of it, but for necessity. As I have stated in my earlier posts, i just will not throw parts at a vehicle unless I'm sure what the problem is. I'm pretty sure I have it right here, just looking for validation from others that have the problem.

Also, I checked my scanner on other O2 sensors, like my Silverado, and it tested correctly on the downstream sensor(s). The upstream sensor(s) were all over the scale as they should be and the downstream sensors were pretty stable, measuring .400 to .500V or so. The Hyundai downstream sensor matched the upstream sensor, showing a failure of the cat.

Anyway, thanks again..I will let you know the results when the cat arrives in the mail, and I install it.

Best Regards,
Steve
 

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sorry to hear the cat is dead. i like my cats, fluffy little ba$tards.

if i had known about it running rich...****. thats a dead giveaway right there.
 

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Discussion Starter #7
yep zero..it was the cat..got the new one, installed it and checked the O2 sensors. Front one switching as normal, rear almost steady. It's great when you research, and check the net, and ask questions to reaffirm what you suspect. And as I stated earlier, I will not throw money at parts if it "could be" the problem. It may take some time, but you can eventually narrow it down!

Thank you for your input, and thanks to this forum. I hope my post and results help someone else!
 
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