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NCT Lambda

  • 11-01-2015 2:11pm
    #1
    Deenie123
    Closed Accounts Posts: 481 ✭✭


    Passed NCT this morning. All fine, but noticed last year's lambda 1.01, this year 1.02.

    Is there anything I can do over the next year to improve that or is it just a case of change the sensor? Or something else?


Comments

  • #2
    Atlantic Dawn
    Registered Users, Registered Users 2 Posts: 84,703 ✭✭✭✭Atlantic Dawn
    M


    Tiny margin of an increase, could be car left idling too long pre test. Car could be cooled down below normal operating temperature. Nothing to worry about.


  • #3
    mickdw
    Registered Users, Registered Users 2 Posts: 23,684 ✭✭✭✭mickdw


    Atlantic Dawn wrote: »
    Tiny margin of an increase, could be car left idling too long pre test. Car could be cooled down below normal operating temperature. Nothing to worry about.

    I wouldnt say it's entirely nothing to worry about. Should be 1.
    .97 to 1.03 is the pass range.


  • #4
    CiniO
    Registered Users, Registered Users 2 Posts: 16,069 ✭✭✭✭CiniO


    IMO absolutely nothing to worry about.
    Most lambda reads I had on NCT were between 0.98 and 1.02.
    Fact that today it was 1.02 doesn't mean that next year it won't be 1.01 or 1.00 or 0.99.
    I'll bet if the tester tested it once again today you could get different result.


  • #5
    Deenie123
    Closed Accounts Posts: 481 ✭✭Deenie123


    For context, the Good Little Car is an 02 Clio. 74,500 miles on it. I was early for the test (having come basically the length of the M50 and then some) so had to do a bit of waiting around with the engine running cos there was zero traffic at all, whatsoever on the way over. I also know of someone with an 01 Clio who had to replace their exhaust recently.

    So I've been frowning at my test report trying to figure out of it's just the drive over followed by sitting with the engine running for ages to keep it warm, or if the exhaust is going, or the sensor.

    By my understanding of it, lambda is the ratio of O2 to exhaust gasses? If so, does that mean my air:fuel ratio is not rich enough?


  • #6
    mickdw
    Registered Users, Registered Users 2 Posts: 23,684 ✭✭✭✭mickdw


    Yep running lean.


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  • #7
    John T Carroll
    Closed Accounts Posts: 757 ✭✭✭John T Carroll


    mickdw wrote: »
    Yep running lean.

    2000 Bora 1.4 with > 180K miles failed (first NCT failure ever) on a Lambda of 1.06, hole in original exhaust suspected, tiny pinholes found in rear silencer so renewed it. Passed retest on a Lambda of 1.02 (CO & HC were OK on all tests). This car highest NCT Lambda since new was 1.006. After renewing the exhaust I measured the average O2 sensor voltage with a VCDS and the average was 0.4027 volts and a fuel trim of minus 1.69%, this with a new O2 sensor fitted which I have had for years and with the new rear silencer fitted. I also took a test with the original (16 year old) O2 sensor and before renewing the rear box and got 0.4065 volts with a fuel trim of minus 1.8%, these readings are almost identical and indicate that the 16 year old O2 sensor is still pretty good, however I will force myself to let the new one in place! as it is probably more reactive under driving conditions.
    What is puzzling me is the fact that the ECU is not increasing the fuel trim to get the average voltage up to 0.45 volt which is a Lambda of 1.0. I carried out an almost identical test on a 2005 Polo and got an analyser average voltage of 0.4543 which is what I would have expected (fuel trim of minus 1.1%) so the only explaination that I can come up with is that either I am reading a slightly lower voltage at the diagnostic plug (on the Bora) or else the ECU is not doing its job as it can increase the trim to at least plus or minus 10% as far as I know, after that I think it flags a emission fault code.


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