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Failed mot on emissions

Discussion in 'Car Repairs / Maintenance' started by Phil78, 11 Jul 2014.

  1. Phil78

    Phil78

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    Hi all, i have a 94 sportrak with 93k on the clock, took it for its test and it needs a few jobs, the one im unsure of is emissions, the fail sheets states "exhaust emissions lambda reading after 2nd fast idle outside limits, LIMIT 1.030 / READING 1.930" i assume 1.930 is very very high considering what the limit is, anyone any suggestions to what the cause could be as im a little unsure.

    Ta Phil
     
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  3. Belle427

    Belle427

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    If all the other readings look ok then i would suspect an exhaust leak of some kind downstream of the lambda sensor. It may not be that apparent but it does not take a lot to alter the readings.
     
  4. Agile

    Agile

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    Why would a leak downstream have any significant effect on the sensor reading?

    Can anyone explain what the Lamda sensor actually reads? My MOT place guy did not seem to have any idea!
     
  5. gregers

    gregers

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    i was offered some advice from a mot tester at my local bus station,prior to any mot drive your car like you stole it,that way everything is up to temperature prior to them doing the test.
     
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  6. chainsaw_masochist

    chainsaw_masochist

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    A Lambda sensor measures the air/fuel ratio present in exhaust gases and should be 14.7 to 1 at normal working temperature. That's why greger's point about "drive it like you stole it" is worth following when you hand it over to the MOT bod.
     
  7. Stivino

    Stivino

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    From Wikipedia;
    An oxygen sensor (or lambda sensor) is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analysed.

    http://tinyurl.com/ydlmy2a
     
  8. Whitespirit66

    Whitespirit66

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    Good advice.

    Another tip for MOTs, is always have your MOT done as the last MOT on a Friday/Saturday afternoon, never first thing on a Monday morning.

    I've always reckoned that human nature being what it is, an MOT inspector will be in a good mood last thing on a Fri/Sat afternoon, as it's the end of the week feeling and poss not long before he goes out with his mates for a few jars. He's more likely to look favourably on any minor faults and put them as advisories. Instead, on a Mon morning, that advisory may be put down as a fail.

    It's not fool proof, but sometimes a bit of psychology can tip the scales in your favour. Rarely lets me down.
     
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  10. xr4x4

    xr4x4

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    Need more info on rest of results.
     
  11. Avocet

    Avocet

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    A high lambda reading means the gas analyser thinks its running very weak. In your case, incredibly so! If the car is running OK and there are no engine management warning lights, I'd start looking for an air leak in the exhaust.

    Because the gas comes out of the cylinders in pulses, there are pressure waves down the exhaust. In the low pressure areas, outside air is sucked into the exhaust, diluting the gas in there. As the MOT gas analyser probe is stuck up the tailpipe, any kind of air leak between the engine and the tailpipe will make the analyser think the mixture is weak (because it has been diluted by atmospheric air).

    It's not the only reason you could have a problem, but it's certainly the first one I'd look for.
     
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  12. Georgereid

    Georgereid

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    Hi Phil,

    Do you have a diagnostic scanner? You can get all the emission data that way.

    If you know anyone that has a USB lead you can try the free version of this software:

    www.obd2software.co.uk
     
  13. Avocet

    Avocet

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    I'm guessing a 1994 car won't have much by way of fault codes to display, though?
     
  14. Georgereid

    Georgereid

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    Sorry about that. After reading all the comments I completely forgot it was 94.

    If I think of anything that can help you, I'll let you know.
     
  15. Agile

    Agile

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    Nearly a month on and what was the outcome Phil ?

    Or are you still on the push bike?
     
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