Engine & Gearbox Driving with possibly faulty cat or o2 sensor

Discussion in '6th Generation (1997-2002)' started by exec, Saturday 31st Jan, 2015.

  1. exec Premium Member Club Supporter

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    So today my EML light came on whilst driving, the obd reader gave the fault code as P0420, so cat/02 sensor related, anyone who read some of my old threads would have read my OEM cat got nicked a while back and I had a cheap crappy after market one installed and an OEM o2 sensor. So I'm guessing the crappy cat has become more crap and sent the o2 sensor into oblivion, can't be arsed getting this fixed, especially going back to the rip off mechanic, as I rather have some custom exhaust fitted at some point or change everything myself for more quality parts, so I'm wondering if I could possibly cause any damage to the car by driving with a faulty cat?

    Cheers
     
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  2. SpeedyGee Administrator Staff Team

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    When the O2 sensor is working, the ECU trims the fuel accordingly, this mode of operation is called "closed loop"
    What happens when you have a fault code thrown for O2 sensor, is that the ECU goes into "open loop", where the ECU uses a fixed single rich fuel map for all conditions.

    So essentially whilst the problem exists, your fuel economy will suffer somewhat.

    It's not detrimental to the engine, just your pocket.
     
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  3. DeviateDefiant Co-Founder Staff Team

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    @SpeedyGee hit out a cracker of an explanation there, just to give some reassurances, my ATR currently has a naff O2 sensor doing the exact same thing - other than running a bit rich and wasting fuel, there's nothing really to worry about. You might also notice a slight knock to power.
     
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  4. Ichiban Founder Staff Team

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    Rich fuel also washes away the oil from the rings and bores which again increases the wear due to lack of lubrication so be mindful of that coked up cat as that rich fuel will end up getting trapped in the cat too.
     
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  5. Chunkylover53 Expert Advisor ★ ★ ★ ★ ★

    Replies above are perfect, have you noticed any effect when driving with the EML?

    Also, do you remember what brand of CAT you had installed? Reason I ask is because I'm supposed to get an aftermarket CAT fitted next weekend so I can sell the genuine one but if these sorts of issues can arise then I won't bother.
     
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  6. SpeedyGee Administrator Staff Team

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    Does your car burn any oil ?
     
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  7. toyracer69 Junior Member ★ ☆ ☆ ☆ ☆

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    Why not just decat it and make sure the secondary O2 sensor has been mounted via an extension piece to stop the MIL from coming on... :Wink:
     
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  8. John Dickson Expert Advisor ★ ★ ★ ★ ★

    @Ichiban is right about rich fuel increasing engine wear. It's like in the days of manual chokes if you ran on the manual choke to long regularly not only did you waste fuel (and stink everyone else out of their cars that were following you) you significantly increased engine wear as you washed the bores clean of the lubricating oil film. Petrol is a solvent so great at removing oil films.

    Not sure about the legalities of a decat.... What happens come MOT time? :Wink:
     
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  9. Harvey Expert Advisor ★ ★ ★ ★ ★

    Think your best bet here would be to go for a stainless system and a 200 cell sports cat, either that or see if you can get a used one from the scrappies, at least to tide you over. However on another not, is your exhaust leaking before or around the o2 sensor?
     
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  10. exec Premium Member Club Supporter

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    Cheers lads, great pieces of info.

    I'm going to continue to drive with it then, i've cleared the code but the problem of course is still there, hopefully should be okay for the short term, but defo don't want to risk engine wear. Going to evaluate in the summer on what to do, I could take it back to the garage that did the work cos the cat should be under warranty, but I rather not since they are a typical rip off merchants like every single other garage.

    I didn't really notice any difference in performance just before the EML came on or after. I was giving the cars some beans when it came on, and stopped immediately on a side road because I thought I must be low on oil, which it sort of was, (so the scummy mechanic probably didn't change the crank seals or the car burns oil cos i :vtec: it a fair amount(?)), topped up with oil, and engine was instantly more smoother afterwards.

    The aftermarket cat brand would have been REACT as it was bought via Euro Car Parts. I would advise you @Chunkylover53 not to sell your OEM one, they are priceless I wish I still had mine :Frown: , the aftermarket cats are dreadful, from the research I did they typically last a year before they need replacing, there is a reason why they cost £60-70 compared to an OEM one which is like £900! You get what you pay for! Annoyingly its probably destroyed the OEM sensor I put on, which i luckily found on ebay for £40, original one is £170!

    @toyracer69 only problem with decat is MOT, getting stopped by police (i don't think its properly legal) and insurance.

    @Harvey I'm seriously considering a custom stainless system with a sports cat, seems like the best route to go and won't cost a bomb, not much more than having it replaced with standard exhausts. But that will need to wait until near insurance renewal time because I will get stung badly with current provider. Not going to put an OEM one on as I know it will get nicked like my last one did. Good point with the leak too, I have a feeling it is leaking somewhere because ever since I got the replacement exhaust fitted on acceleration it makes a whisper noise, was loud at start but has faded a bit, plus point of that is it makes it sound like i have a turbo fitted :Devil: I think I need to go under the car and inspect both the oil and exhaust again, shame the weather has gone cold recently :thumbdown:
     
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  11. Harvey Expert Advisor ★ ★ ★ ★ ★

    One way of finding an exhaust leak is to get a mate to plug the tailpipe briefly, so you can hear the leak much better, as its forcing gasses out of the hole. You are correct, insurers will sting you for declared mods, maybe not such much for an exhaust if its the same size as standard and not a performance one. Or at least tell them that :Smile:. Admittedly I neglected to mention I fitted a spoiler to my car, but it is a genuine honda part and was fitted to hatchbacks as an optional extra.

    your right about the cold though, I had to replace my PSF bottle today after I broke it changing the fluid, wasnt best pleased.
     
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  12. exec Premium Member Club Supporter

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    ^ Yep will do that. The other thing with the current insurer i'm with is that the price that they gave me was ridiculously cheap (compared to old insurers and everyone one else), and they sent me a letter a week later saying it was a mistake on their system but they will honor it, but any changes to the policy would recalculate the premium!

    Personally think its pointless declaring OEM stuff, just claim it was on there when you bought it, it doesn't really make any difference to a car of that age, i don't get why insurers bother, perhaps just another way of fleecing money from customers?

    Going back on the topic of o2 sensor, I thought the sensor that is on the cat doesn't actually really do anything? Isn't the one that is fitted in the manifold that does the job of collecting emissions and regulating etc, and the cat one only monitors health of the cat?
     
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  13. Harvey Expert Advisor ★ ★ ★ ★ ★

    As for insurers, probably for fleecing customers.


    I'm not sure what the second sensor is for, like you said probably for monitoring that the cat is doing its job.
     
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  14. John Dickson Expert Advisor ★ ★ ★ ★ ★

    Good point @Harvey never thought of that!

    I remember I had a K11 Micra once and every MOT it sailed through particularly emissions test it was clean as a clean thing.

    Then one time it failed on emissions test the lambda reading was way off. It was a leak in the exhaust system but it wasn't even a noisy leak so I never noticed it but it was sufficient to send the lambda reading crazy.
     
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  15. Harvey Expert Advisor ★ ★ ★ ★ ★

    It doesn't take much of a leak to set the lambda off. But I know what ya mean, never had that problem though.
     
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  16. John Dickson Expert Advisor ★ ★ ★ ★ ★

    Now I think about it I think it was actually a leaking gasket rather than a section of exhaust pipe.
     
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  17. Harvey Expert Advisor ★ ★ ★ ★ ★

    leaking gaskets are not so bad, though having a cracked manifold is worse, that means even more parts to buy, but the bonus that the leak goes away completely when they both get replaced.
    At least it was like a mate of mine who had an engine light on for a failed cat, but the car was the exhaust manifold as well! nearly £200 just for an aftermarket replacement!
     
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  18. John Dickson Expert Advisor ★ ★ ★ ★ ★

    Yes I was glad it was only a leaking gasket and they managed to separate the two sections, replace the gasket and get it back together. Saved having to replace the exhaust sections.

    Nissan use OEM Calsonic Kansei exhausts. When it came time to replace it I went for Calsonic system again. It only had a 1 year warranty and after market exhaust came with 3 year warranty but the difference in weight between them was amazing. Non-OEM was like it was made of paper and despite the 3 year warranty the Calsonic system was identical to the one I was replacing which had done 9 years so the shorter warranty was immaterial to me as I knew I was getting the better exhaust.
     
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  19. Harvey Expert Advisor ★ ★ ★ ★ ★

    I had to replace the echaust on my Accord when i got it, and i think that might well have been the origonal system, which had done 14 years, The replacement mid section was £60 and the backbox was about the same, and although the back box is a Bosal one which in itselt is not a bad part, the whole lot doesnt sound as sweet as it could. There seems to be alot of undue noise, not from blowing, i can't put my finger on it, but its something an OE system wouldn't do, but the cheap ones do because they are inferior quality, plus the backbox doesnt sit straight because I think the centre section isnt shaped properly.
     
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  20. exec Premium Member Club Supporter

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    ^ I know what you mean with any aftermarket exhausts, I had my exhausts replaced, mid and rear not long after I bought my car by kwik Fit, who I think use bosal parts and there was always this noise to it, actually sounded like it was blowing somewhere, but it wasn't, as I checked it all out and even went back to the kwik fit guys to check it over and they couldn't find any issues.

    Anyway went for a drive yesterday night, and on startup I revved a bit and I can hearing sort of blowing noise from under the front row seat area, so possibly it is leaking, also string smell of petrol, although its done that long before, probably just cold start using petrol.

    Also I came across a very nice S2000 yesterday and had a tussle with it, noticed I still have issue with VTEC where sometimes it drops revs and lunges forward, thought it was fixed when the crank seal was replaced, guess not! Which adds to my suspicions of whether it was really changed, but the issue could be elsewhere.
     
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