Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie
Please note that it is not permitted to have referral links posted in your signature. Keep these links contained in the appropriate forum. Thank you.

https://www.boards.ie/discussion/2055940817/signature-rules
Hi there,
There is an issue with role permissions that is being worked on at the moment.
If you are having trouble with access or permissions on regional forums please post here to get access: https://www.boards.ie/discussion/2058365403/you-do-not-have-permission-for-that#latest

NCT fail ? Really ?

  • 09-03-2015 11:23am
    #1
    Mar4ix
    Registered Users, Registered Users 2 Posts: 2,352 ✭✭✭


    Hi folks, just a quick question.

    My friend has car, Audi A4 , 1.8 T , petrol, 02, failed NCT on lambda/oxigen sensor value too high (1.12 ) , However emissions are spot on , low revs 0.08, high revs 0.01 .

    Cant understand that, if lambda shows wrong numbers, how does it affect pollution or safety ???

    Sorry, bit angry ...


Comments

  • #2
    CiniO
    Registered Users, Registered Users 2 Posts: 16,069 ✭✭✭✭CiniO


    Emissions of what are 0.08 and 0.01?

    Lambda like that indicated there's something wrong.
    It's either lambda sensor itself or just car is running on too rich mixture.
    Too rich mixture would cause extra pollution and possibly will damage cat converter fairly soon.
    Something definitely should be looked up and it's good it's an NCT fail.

    EDIT: My mistake.
    Lambda above 1 indicates leax mixutre, not rich.


  • #3
    Mar4ix
    Registered Users, Registered Users 2 Posts: 2,352 ✭✭✭Mar4ix


    car idles and drives without any issues. Last year passed nct without issues. this year only lambda value is out of expected 0.98-1.03, meanwhile emissions are spot on.

    My friend have put second (used one) oxygen sensor, which also failed NCT , still good emissions, only value was better for a very little bit.

    CiniO , you think there is something wrong with engine ? Unburnt gases passes catalytic converter , which does the job, so second lambda keep quiet ? No faults shown about first lambda either. No misfire or smoke.

    I have done diagnostics with wag-com, and all lambda values was within acceptable scope , no faults in engine management, MAF is spot on.

    I dont know what to think off.


  • #4
    wonski
    Registered Users, Registered Users 2 Posts: 13,685 ✭✭✭✭wonski


    CiniO wrote: »
    Emissions of what are 0.08 and 0.01?

    Lambda like that indicated there's something wrong.
    It's either lambda sensor itself or just car is running on too rich mixture.
    Too rich mixture would cause extra pollution and possibly will damage cat converter fairly soon.
    Something definitely should be looked up and it's good it's an NCT fail.

    CO I guess.

    OP - there is something wrong, just because the other values are within limits doesn't mean you should pass.


  • #5
    Mar4ix
    Registered Users, Registered Users 2 Posts: 2,352 ✭✭✭Mar4ix


    wonski wrote: »
    CO I guess.

    OP - there is something wrong, just because the other values are within limits doesn't mean you should pass.


    obviously CO yes.

    Just one thing, would a small hole down to exhaust would affect lambda ? Really doubt it. .. it is turbocharged engine, and less back pressure (after turbocharge) even better, (not shown in fault list about leaking exhaust) ...

    usually naturally aspirated engines are sensitive to leaks in exhaust .


  • #6
    kona
    Registered Users, Registered Users 2 Posts: 7,525 ✭✭✭kona


    You mates car is running lean, sounds like it's a leak in the exhaust downstream of 1st lambda.

    First lambda is what the ECU uses the control the fuelling.


  • Advertisement
  • #7
    Eric Cartman
    Registered Users, Registered Users 2 Posts: 26,280 ✭✭✭✭Eric Cartman


    Mar4ix wrote: »
    obviously CO yes.

    Just one thing, would a small hole down to exhaust would affect lambda ? Really doubt it. .. it is turbocharged engine, and less back pressure (after turbocharge) even better, (not shown in fault list about leaking exhaust) ...

    usually naturally aspirated engines are sensitive to leaks in exhaust .

    Hole in exhaust would mess up lambda values if its before the sensor. Could potentially cause the car to run rich


  • #8
    wonski
    Registered Users, Registered Users 2 Posts: 13,685 ✭✭✭✭wonski


    Mar4ix wrote: »
    obviously CO yes.

    Just one thing, would a small hole down to exhaust would affect lambda ? Really doubt it. .. it is turbocharged engine, and less back pressure (after turbocharge) even better, (not shown in fault list about leaking exhaust) ...

    usually naturally aspirated engines are sensitive to leaks in exhaust .

    Wouldn't do any harm to do a bit of welding if it is small enough.

    My lambda failed due to leaking exhaust, it was a big hole though ( started a thread 2 years ago on that i think found it: http://www.boards.ie/vbulletin/showpost.php?p=78175191&postcount=1


  • #9
    neasyerac
    Registered Users, Registered Users 2 Posts: 245 ✭✭neasyerac


    Mar4ix wrote: »
    obviously CO yes.

    Just one thing, would a small hole down to exhaust would affect lambda ? Really doubt it. .. it is turbocharged engine, and less back pressure (after turbocharge) even better, (not shown in fault list about leaking exhaust) ...

    usually naturally aspirated engines are sensitive to leaks in exhaust .

    My Subaru legacy 2.0 TT failed on lambda last year, Emissions were spot on though turns out there was a little hole along the exhaust and was messing up lambda results. Quick fix for the mechanic and passed on my retest.


Advertisement