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MoT query - not classic

Here's another MoT test query for those in the know, before I query with the garage...

The wife's '99 Clio 1.4 failed today due to

"Rear silencer blowing" - OK "Emissions above limits due to rear silencer (lambda sensor)" - ????

The lambda sensors (I think there are two) are ahead and behind the cat on this car, measuring O levels downstream of the engine. The rear box is downstream of this - how can a blowing rear silencer alter the emissions reading, especially "higher". When my wife (she's a canny sod) asked the mechanic for the emissions test printout he said there wasn't one "'cos it had failed".

I'm guessing he didn't even do the emissions incorrectly (perhaps?) assuming all was lost due to the rear silencer.

Gentlefolk, your opinions are valued...

-- Ken Davidson

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Reply to
DocDelete
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She should have got a print out even if it had failed, but that`s something to take up with the garage in question. A blowing exhaust can cause emmissions test failure. Even thought he sensors are before the blow, the analyser senses what comes out of the exhaust. The blow will cause an inncorrect mixture at the tailpipe. It is usually the HC measurement that is the one that fails and not the CO, CO2 etc. I`ve known this happen with newly fitted exhausts that haven`t had time to seal or not been sealed correctly. So to answer your question, yes a blowing exhaust will cause an emmision test failure, but you should have had a print out. 2 printouts of every test are manadatory.

Reply to
robby

The lack of backpressure will confuse the system.

MrCheerful

Reply to
MrCheerful

Well if it's blowing then the air that gets sucked in the exhaust will confuse the lambda sensor on his emissions tester. Still new exhuast box is easy & only £25+Vat

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Reply to
Duncan Wood

A pal of mine took his car for an MOT once and was told it had failed on the emmissions. When he queried the lact of a printout and insisted on getting one, the tester went away for a bit, came back and said sorry no printout but the car hadn't failed after all ?????

If they can't give you the printout theres a fair chance they were pulling a fast one.

Reply to
Doug

The MOT as well as measuring CO also measures O. Any leaks in the exhaust system will suck extra O in pushing the limit over. A lot of people have changed Lamdda sensors when they've just got dodgy joints in their exhaust.

John

Reply to
John Greystrong

the exhaust what comes out of the tailpipe will not be the same as comes out of the engine ...... the MOT testers machine doesnt know this and if the reading is out side the prescribed limits , you fail . steve the grease

Reply to
R L Driver

Thanks again all - I can see also see why a lack of exhaust pressure from the proper hole (tailpipe) due to a large blow can fail to pump the probe too. I guess my main quibble was the lack of emissions test print out - maybe I'm too suspicious / cynical for my own good.

Anyway, it'll be sorted - and thanks to Duncan Wood for the link to BuyPartsBy.

-- Ken Davidson DocDelete

Reply to
DocDelete

Wow didn't know about the parts website at the bottom. Got some great prices on exhaust system parts.

Cheers.

Reply to
David Cawkwell

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