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Thread: 1.4 TSI ACT Failed Emissions - Help

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  1. Re: 1.4 TSI ACT Failed Emissions - Help 
    #31
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    I too believed it's the testers machine when the MOT failed. But since then 2 other garages I've taken it too have confirmed the same levels of CO, consistent with MOT readings.

    So yes I asked the same question to the technicians as to why the post-CAT lambda sensor wasn't picking this high percentage and they didn't have a clue ?

    Where about are you based, in case I can potentially drive it to yourself and hope for an answer.
     
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  2. Re: 1.4 TSI ACT Failed Emissions - Help 
    #32
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    What a turnaround - Took the car to Audi today for Service (oil change + MOT) and had already made them aware that it has failed MOT due to high emissions. They did some diagnostics and came back saying the pre-CAT lambda is faulty. I told them it has been changed just 2 weeks ago by a VAG specialist and that hasn't really helped.

    They took the car for MOT and it just flew through the MOT with no issues at all and a 0.01% CO emission. Couldn't believe it when they showed me the test results. Although they insisted the sensor that VAG specialist have put is not a genuine Audi part and they have not set up the lambda sensor correctly - something called Basic Ageing setting is not done.

    So, I went back to my local VAG with the Audi report and they said there's no setting for Ageing or anything like that and they did another exhaust check for me and it went flying through with 0% emissions. They were insinuating thought that Audi might have done some software tweak or reset something in ECU to lower the emissions, although I don't think they would have done that without telling me or charging for the same.

    I am still keen to understand what had happened and how did the whole thing just magically fix within a week after putting the new lambda sensor. Even though the emissions were still high when VAG tested after putting the new sensor. Does it take time for the sensor to regulate and fix the emissions ?

    Still confused 😕 as before but much relieved after the MOT pass. 😌
     
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  3. Re: 1.4 TSI ACT Failed Emissions - Help 
    #33
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    It's almost like they did something to help it lower the emissions while being tested ...
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  4. Re: 1.4 TSI ACT Failed Emissions - Help 
    #34
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    I had just been doing some research when I came across this thread.
    There seems to be an awful lot of misinformation within this thread which will unfortunately lead people astray who are trying to solve problems with their own cars.
    There’s far too much to respond to it all but let me add this information as I am a qualified professional mechanic and this info will help folks.

    Firstly, there are hundreds of faults that can occur without illuminating a warning lamp or setting fault codes. This is often but not always due to sensors creating a signal that’s within the normal range of operation but is in actual fact an incorrect signal/value.

    Next the idea that a car fuel injection system and more so the lambda sensors are more technical or complex than an MOT station gas analyser is ridiculous and some what funny. A lambda sensor senses oxygen and nothing else. It cannot detect co/co2 etc. The MOT station gas analyser can detect co/co2/lambda and hc is detected in parts per million.

    The most common reason why a garage cannot find a problem or cannot find a fault is because they don’t know what they are doing with diagnostic machines or how to interpret the live data, to put it simply they aren’t trained or experienced enough. Turning sockets and spanner’s is very easy and most can do this with a manual or some training. It takes a lot more brains to understand how it all works and how to interpret the systems sensor outputs.

    Co is basically unburned fuel or oil.
    In my experience the most common causes of high co emissions are the following;
    Bad pre cat o2 sensor.
    Ignition system misfires.
    Bad pcv valve.
    Excessive crank case pressure.
    Boost leaks.
    Leaky evap purge valve.
    MAF sensor fault.
    Catalyst deficiency. (Bad cat)
    The list does go on, anything that can upset a/f ratio is also suspect.
    Another common cause of cars failing the mot on co only is due to MOT testers not heating the engine and cat up enough for the cat to work properly.

    When diagnosing a high co condition all the other info from the MOT emissions print out are taken into consideration as all gases are indicators to combustion quality. Other factors are included when making decisions too. For example if co is high and hc is high but within limits then you know you have excessive unburnt fuel or a lack of air. All the clues lead you in the diagnostic one step at a time.

    I’m a member of a bunch of forums and have been for years. I don’t mind helping folks out when I have time by giving advice for free. I’ll pop back over here at some point and see if anyones stuck.

    Cheers
     
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