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Passed mot with decat

Discussion in 'A4/S4 forum(B5 Chassis)' started by jamie226bhp, Jul 19, 2011.

  1. jamie226bhp
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    jamie226bhp Member

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    [Jul 19, 2011]
    Just a random post but just mot my car and it passed the emissions even with a decat fitted anyone else had this as I was sure it would fail and I'd have to refit it
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  3. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Jul 19, 2011]
    Mince.

    Tester has let it slip, or shoved the probe up something else.
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  4. Oranoco
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    Oranoco Well-Known Member

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    [Jul 19, 2011]
    It has been known when testing emissions for the probe to end up in the wrong cars tailpipe. It is an accident and simply down to the number of cars and MOTs performed.








    *snigger*
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  5. B5NUT
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    B5NUT Well-Known Member VCDS Map User

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    [Jul 19, 2011]
    My 1.8T also passed with a decat (unknown to me) I was told the emissions were high and the tester said the cat must have been on it's way out. When I got around to fitting a new cat I found the guts had been nocked out of the old one.
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  6. gary3306
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    gary3306 Member VCDS Map User

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    [Jul 19, 2011]
    I am an authorised examiner and on an MOT test, the exhaust is only checked for structural integrity, security and for severe leakage (a minor blow is an advisory). It will NOT be a failure in itself if the cat has been removed. If the car can come within the limits set on the emissions or smoke test, then it will pass, simple as that. If it fails the emission/smoke test on excessive output, then it will fail on that alone as the tester can not say whether it is the omission of the cat that has caused the high emissions/excess smoke, or another factor (say faulty engine temp sensor for instance). On my forum it has come up time and time again, members asking will my car fail its MOT if the cat isn't on. The definitive answer; If it can pass the emissions/smoke test, then NO it will not fail.
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  7. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Jul 19, 2011]
    Theres simply no way a petrol engined car can pass the cat emissions test without a catalytic converter.

    To get the CO below 0.3% without a cat, you'd need to lean the mixture out to such at extent that it would fail due to too much O2 in the exhaust instead plus modern engines all have lambda sensors keeping the engine at lambda 1 anyway, so you cant lean it out at all.

    Most engines when running at lambda 1 without a cat will emit between 0.5 and 0.7% CO, and as such, will fail.
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  8. B5NUT
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    B5NUT Well-Known Member VCDS Map User

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    [Jul 19, 2011]
    Well my car passed. The tester did not stick probe up another car, he would have just failed the car. I only found the decat after I removed the old cat as I purchased a new one when I was told the emissions were almost at the level of failure.
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  9. gary3306
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    gary3306 Member VCDS Map User

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    [Jul 19, 2011]
    well its not impossible for them to pass, but its rare. I'm just making the basic point that a 'missing cat' is not a reason for failure in itself.
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  10. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Jul 19, 2011]
    Our old A4 was exactly the same when we baught it. Failed emissions with 0.49% CO but perfect lambda value. I assumed the cat was just worn out. Took it off and the old one had been gutted.

    B5NUT: You got the emissions test printout from the so called marginal test?
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  11. B5NUT
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    B5NUT Well-Known Member VCDS Map User

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    [Jul 20, 2011]
    Yes, it will be filled away will try and find it tomorrow. When I bought the car I had no idea someone had taken a hammer to the cat as there was no external evidence of someone bashing the stuffing out of it.
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  12. jamie226bhp
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    jamie226bhp Member

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    [Jul 20, 2011]
    I always throw my emission test paper wish I'd kept it now to post it up here
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  13. ScottD3
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    ScottD3 I want your faulty electronics

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    [Jul 20, 2011]
    My BMW past 2 MOTs with no cats, no mods, no nothing.
    Cats removed and mot past.
    I don't think its as clean cut as you say it is.

    I all ways thought cars after a set year had to have a cat (or what looks like a cat) in place to pass and emissions was just another test.
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  14. Oranoco
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    Oranoco Well-Known Member

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    [Jul 20, 2011]
    Nope, there is no rule that says a cat must be present. Only that it has to pass a strict emmision test. Without a cat it is unlikely you will pass, but not impossible
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