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Discussion Starter #1
My old ship passed another MOT but I noticed that his emissions were on the high side (just inside the MOT Test limit).

I reckon one of these years it'll go just over and fail.

What sorts of thing(s) can I do to get the reading down next year (other than replace my valve guides/piston rings/ECU/Catalyst/engine etc.) ?

I only came up with "New air filter".

Ralf S.
 
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Discussion Starter #2
The dreaded lambda probe can be replaced eek!

Marlon
 
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Discussion Starter #3
You can try a general service before hand & checking the fuel pressure\fueling. Oh & checking there are no air leaks into your vaccum hoses as this also can affect emission\fueling.
 
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Discussion Starter #4
Also take it for a good run, about 10-20 mins down a dual carriageway before the test. Not too fast though eek!

wrinx
 
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Discussion Starter #5
Fuel Injector cleaner worked for mine. It failed on emmisions two years ago and once the injector cleaner was added to the fuel and run for a few minutes it passed. It also passed the following year so I wouldn't be to worried about it.
I have also been told about a Subaru WRX without a Cat that passes the MOT. It has an MOT setting on the ECU which enables it to pass the MOT, but it only produces about 21 BHP.
Ian.
 
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Discussion Starter #6
Would've thought they'd fail the car simply for not having a Cat as its standard equipment???

wrinx
 
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Discussion Starter #7
No.. the standard is tighter for (originally) Cat-equipped cars but if they can pass without one then it's no bother not actually having it.

Ralf S.
 

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I enquired about the cat/mot issue from Adrian of Alfa Aid (recommended) when I wanted to decat my RZ. He says that any vehicle has to have a cat if it was registered on August 1992 or later to pass an MOT irrespective of it meeting emissions without one. Adrian is a registered MOT tester.

Regards

Phil
 
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Discussion Starter #9
thats true, unless you can prove its got an older engine in it that doesnt need cat testing.
 
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Discussion Starter #10
What about the Cat' itself?

Do they wear out (get less efficient) with age, or is it a case that if the emissions are too high for the MOT then a new Cat' isn't going to help?

I like the idea that changing the lambda probe can give me reduced emissions (how much is it?) but if I have to replace engine bits and catalysts then that'll need budgeting for beforehand.

Ralf S.
 
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Discussion Starter #11
Cats where origonally supposed to last 60k miles, there were lots of stories about how fragile and sensitive they are. However, I've only ever heard of them being replaced due to the casing corroding, not the internals failing (unless they get contaminated!).

Usual problem, especially on 155's, seems to be the lambda probe.

wrinx
 
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Discussion Starter #12
Ralf, the probe from an Alfa dealer is ~£65.
You can get cheaper universal ones but you have to cut and join wires. I personally replaced mine with an Alfa part, although some people here have used Uni parts and found them no problem.

Marlon
 
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Discussion Starter #13
the insides of cats also fall apart and rattle around inside.a faulty cat cant increase emissions.!
 
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Discussion Starter #14
jimybob:
the insides of cats also fall apart and rattle around inside.a faulty cat cant increase emissions.!
Hows that then? The cat changes the exhaust gases by chemical reaction to produce carbon dioxide (think thats the one!), if its knackered then the emissions would be higher.........surely? Or, is it that the cat only cleans the gases more but emissions would still be in range 'cos of the lambda action?

wrinx
 
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Discussion Starter #15
How Catalytic Converters Reduce Pollution

Most modern cars are equipped with three-way catalytic converters. "Three-way" refers to the three regulated emissions it helps to reduce -- carbon monoxide, VOCs and NOx molecules. The converter uses two different types of catalysts, a reduction catalyst and an oxidization catalyst. Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium. The idea is to create a structure that exposes the maximum surface area of catalyst to the exhaust stream, while also minimizing the amount of catalyst required (they are very expensive).

There are two main types of structures used in catalytic converters -- honeycomb and ceramic beads. Most cars today use a honeycomb structure.

The Reduction Catalyst

The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2. For example:

2NO => N2 + O2 or 2NO2 => N2 + 2O2

The Oxidization Catalyst

The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. For example:

2CO + O2 => 2CO2

But where did this oxygen come from?

The Control System

The third stage is a control system that monitors the exhaust stream, and uses this information to control the fuel injection system. There is an oxygen sensor mounted upstream of the catalytic converter, meaning it is closer to the engine than the converter is. This sensor tells the engine computer how much oxygen is in the exhaust. The engine computer can increase or decrease the amount of oxygen in the exhaust by adjusting the air-to-fuel ratio. This control scheme allows the engine computer to make sure that the engine is running at close to the stoichiometric point, and also to make sure that there is enough oxygen in the exhaust to allow the oxidization catalyst to burn the unburned hydrocarbons and CO.

So I think if the cat isn't working, the Carbon Dioxide (CO2) level won't be too high in an MOT test. Don't think they test for Carbon Monoxide do they ???

Marlon
 
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Discussion Starter #16
That's cleared up then. My NOx is okay - it was the CO2 readings that were pushing the limit.

Funny that they don't measure CO - that's the poisonous one, isn't it?

Ralf S.
 
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Discussion Starter #17
eerrr co/hc and lambda are the only things measured not co2...wrinx a faulty cat can't increase emissions beyond what it would be if one were not fitted..marlon where did your info come from. :)
 
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Discussion Starter #19
Mine has just scraped through the MOT and took three attempts for the emissions to be acceptable.
About 6 months ago the engine temp. sensor failed, the resultant effect being a misfire upon application of the throtle and then gradualy becoming much worse, to a point where it would stall if the revs dropped to below 3000 nessecatating a few high speed bump starts. Not good for the Cat.
Once the sensor was fixed the emissions were way to high for the MOT, but over the past 6 months the cat has had time to purge itself and come back to life.
This Cat has done 165000 miles and is still functioning.
This leads me to one of two possible conclusions which are
1)These Cats are very robust and can take a lot of abuse.
2)They're not needed.
 
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Discussion Starter #20
Hi I'm new to this group!

Anyway

If the MOT station thinks you have a cat fitted will they fail you i.e. a straight through pipe made to look like a cat?
Also how much bhp as a percentage do they rob from the output?
If they are full of expensive(?)metals do they have a high scrap value?(i.e can you offset this price against a new one or sell it to a matal recycler yourself?)

Hope you can answer my query
Funkin Go-nut
 
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