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1995 Fiat Punto failed NCT - lambda high

  • 16-09-2017 7:54pm
    #1
    selfdiy
    Registered Users, Registered Users 2 Posts: 183 ✭✭


    Hi Folks,

    I'm looking for some advice on a 1995 Fiat Punto which failed the NCT on emissions with the following readings.

    High Idle
    Lambda 1.31 should be between 0.97 and 1.03 -- fail
    CO 0.04% Not above 30% -- pass
    HC 40 ppm Not above 200 ppm -- pass

    So it only failed on the lambda.

    I bought a cable and connected the ecu to my laptop.
    No error codes were stored.

    The live data for "Lambda Probe Correction" goes up and down on the graph
    The live data for "Lambda Sensor in Closed Loop" graph also goes up and down when the engine is revved.

    All tests pass, coils, injectors etc.

    Car runs great, I'm at a loss with what todo with it next?
    Any advice would be greatly appreciated.


Comments

  • #2
    jca
    Closed Accounts Posts: 8,585 ✭✭✭jca


    Have you a leak in the exhaust somewhere? Maybe there's a leak around the manifold somewhere.


  • #3
    scannerd
    Registered Users, Registered Users 2 Posts: 236 ✭✭scannerd


    High reading is normally down to 02 sensor faulty, the mixture may be too weak or there may be a hole in the exhaust.

    exhaust hole is simplest to check for - start there, even very small blow will impact

    02 sensors soft fail and still go up and down on the scan tool, they may be too slow or not moving enough, but yours sound alive at least.

    check you long and short term fuel trims, if staying high all the time then check fuel pressure


  • #4
    selfdiy
    Registered Users, Registered Users 2 Posts: 183 ✭✭selfdiy


    Thanks for the replys, I'll check more thoroughly for leaks but I'm pretty sure there are none.

    I have some screen shots the lambda sensor graph will try to post

    Photo%2016-09-2017%2C%2015%2010%2058.jpg?raw=1


  • #5
    jca
    Closed Accounts Posts: 8,585 ✭✭✭jca


    Lambda as stated on the sheet means how rich or lean the mixture is at the exhaust tailpipe. 1.00 is perfect anything below that is rich and anything above 1.00 is too lean, as your CO figures are within the pass parameters it means the O2 sensor is doing its job. Air is entering the exhaust system somewhere and leaning the exhaust gases.


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