29 replies to this topic

[cambiker71]

A couple of questions,
what age is the car?
is this all it failed on?

I'm an MOT tester, and i think the test may have been caried out incorrectly.

[Mrs Emma]

A couple of questions,
what age is the car?
is this all it failed on?

I'm an MOT tester, and i think the test may have been caried out incorrectly.

Sadly not the only thing she failed on!
Split CV gaiter,
Suspension ball joint dodgy
Binding rear brakes
No argument about all the above - it was the replacement of the Cat that I was doubtful about!

94M with carb and cat by the way.

Thanks!

[cambiker71]

A couple of questions,
what age is the car?
is this all it failed on?

I'm an MOT tester, and i think the test may have been caried out incorrectly.

Sadly not the only thing she failed on!
Split CV gaiter,
Suspension ball joint dodgy
Binding rear brakes
No argument about all the above - it was the replacement of the Cat that I was doubtful about!

94M with carb and cat by the way.

Thanks!

The procedure for a car of this age is to do a basic emissions check first, then if it fails it goes to a full vehicle specific catalyst test.
to do this test info from the car i.e. the chassis and/or engine number must be an EXACT match to a vehicle on the VOSA database, not a near match it has to be EXACT, If it has fuel injection there will be a match and the limits are set, if it has a carburettor then there won't be an exact match as the database only includes fuel injection cars with a closed loop catalyst set up and the test should be done at idle speed using the following limits
Idle speed must not be obviously too high
3.5% CO content at idle speed
1200ppm HC at idle
OR
if it cant pass the HC limit at IDLE then the engine should be raised to around 2000 rpm and rechecked, if below 1200 ppm then it passes. but the CO content must only be checked at a normal idle speed

So it looks like the emissions for your vehicle should have passed, you don't need a cat at all either if it's relevant.
hope this makes things clear

[minibob]

A couple of questions,
what age is the car?
is this all it failed on?

I'm an MOT tester, and i think the test may have been caried out incorrectly.

Sadly not the only thing she failed on!
Split CV gaiter,
Suspension ball joint dodgy
Binding rear brakes
No argument about all the above - it was the replacement of the Cat that I was doubtful about!

94M with carb and cat by the way.

Thanks!

The procedure for a car of this age is to do a basic emissions check first, then if it fails it goes to a full vehicle specific catalyst test.
to do this test info from the car i.e. the chassis and/or engine number must be an EXACT match to a vehicle on the VOSA database, not a near match it has to be EXACT, If it has fuel injection there will be a match and the limits are set, if it has a carburettor then there won't be an exact match as the database only includes fuel injection cars with a closed loop catalyst set up and the test should be done at idle speed using the following limits
Idle speed must not be obviously too high
3.5% CO content at idle speed
1200ppm HC at idle
OR
if it cant pass the HC limit at IDLE then the engine should be raised to around 2000 rpm and rechecked, if below 1200 ppm then it passes. but the CO content must only be checked at a normal idle speed

So it looks like the emissions for your vehicle should have passed, you don't need a cat at all either if it's relevant.
hope this makes things clear

I agree with Cambiker71, Should have passes and the cat is irrelevant, I have a '93 carb sprite and have had no problem with emissions on MOT even after replacing the exhaust a couple of years ago and getting rid of the cat in the process. I take it to the local borough council MOT centre every year and the chap there always mumbles about dates and how it unusual to have a carb with that first registered after such a date. I enjoy it as I get to help him with the test by sitting in the car and doing all the controls when he says... anyway hope you get it all sorted.
Nat

[Mrs Emma]

Just a final update - After going to see the garage yesterday, it sounds like it's a case of "computer says no" really. They are adamant that when my min's details were put into the system that it came up as needing the test that they did.

So am biting the bullet and replacing the cat, and then putting it in for a partial retest*

All of your advice has been fantastic though so thanks v. much! It goes without saying that a mini friendly test centre will be used next year!

*And if she fails again there will be trouble!

[mini_kel]

NO NO NO go somewhere else!!!!, Why pay out for a cat when you don`t need one! And i guess you are going to have to pay for retest anyway? There must be another MOT garage nearby??

Did they look through the handbook???

Edited by mini_kel, 08 August 2008 - 09:45 AM.

[Rhyd]

Replacing the cat will make no difference - the mixture's way too weak. You could put 12 cats in series and it still wouldn't work.

Save yourself a few hundred quid and the the mixture adjusting screw / nut turned! Then it WILL past the test they're doing.

As your tester clearly hasn't got a clue what CO, HC and Lambda readings actually mean, go somewhere else. Tell them you need an MOT, but you want them to set the mixture for you first - meaning that either they set the mixture right and it'll pass the emissions test, or they can't get the mixture right and won't do the MOT either.

[cambiker71]

Just a final update - After going to see the garage yesterday, it sounds like it's a case of "computer says no" really. They are adamant that when my min's details were put into the system that it came up as needing the test that they did.

So am biting the bullet and replacing the cat, and then putting it in for a partial retest*

All of your advice has been fantastic though so thanks v. much! It goes without saying that a mini friendly test centre will be used next year!

*And if she fails again there will be trouble!

Seriously, if you have a carburettor and not single point injection, then IT IS NOT on the database, i have overall responsibility for the MOT station i work for, take my word for it. Ask them for a VT17 appeal form and get in touch with VOSA. You don't need a mini friendly test station, just one that knows how to follow simple instructions and can do it's job properly. Sorry if this post sounds blunt, but i spend every day ensuring we do a good and professional job and it really annoys me to read things like the above.

[cambiker71]

Replacing the cat will make no difference - the mixture's way too weak. You could put 12 cats in series and it still wouldn't work.

Save yourself a few hundred quid and the the mixture adjusting screw / nut turned! Then it WILL past the test they're doing.

As your tester clearly hasn't got a clue what CO, HC and Lambda readings actually mean, go somewhere else. Tell them you need an MOT, but you want them to set the mixture for you first - meaning that either they set the mixture right and it'll pass the emissions test, or they can't get the mixture right and won't do the MOT either.

You're part right, but these reading are about right for a carburettor car with a cat, the cat cleans it all up and gives weak looking readings, checking the emissions should really be done pre cat for tuning purposes, there used to be a pipe from exhaust down pipe to beside the engine top tie bar that readings could be taken from to set it up properly.

Fast idle test
CO 0.03% (pass)
HC 0014ppm (pass)
Lambda 1.198 (fail)

2nd Fast idle test
CO 0.04% (pass)
HC 0 023ppm (pass)
Lambda 1.217 (fail)

Natural Idle test
CO 0.05% (pass)

[Sprocket]

Replacing the cat will make no difference - the mixture's way too weak. You could put 12 cats in series and it still wouldn't work.

Save yourself a few hundred quid and the the mixture adjusting screw / nut turned! Then it WILL past the test they're doing.

As your tester clearly hasn't got a clue what CO, HC and Lambda readings actually mean, go somewhere else. Tell them you need an MOT, but you want them to set the mixture for you first - meaning that either they set the mixture right and it'll pass the emissions test, or they can't get the mixture right and won't do the MOT either.

You're part right, but these reading are about right for a carburettor car with a cat, the cat cleans it all up and gives weak looking readings, checking the emissions should really be done pre cat for tuning purposes, there used to be a pipe from exhaust down pipe to beside the engine top tie bar that readings could be taken from to set it up properly.

Fast idle test
CO 0.03% (pass)
HC 0014ppm (pass)
Lambda 1.198 (fail)

2nd Fast idle test
CO 0.04% (pass)
HC 0 023ppm (pass)
Lambda 1.217 (fail)

Natural Idle test
CO 0.05% (pass)

That is a classic leaky exhaust reading. The exhaust is leaking after the lambda sensor!!! Where fitted

That cat is working and doing its job!

[peekachoo]

I've heard it said that there's an addendum at the back of the MOT Testers Handbook that clearly states that regardless of age, any Mini fitted with a carburettor need not be tested for a catalytic converter?

So tell him to look at the back of his book.

Does anyone have the exact reference for this info ??

Maybe on here http://www.motuk.co.uk/manuals.htm ??


My car has just failed it's MOT on emissions with almost exactly the same readings as quoted in this thread.

Thanks

[Sprocket]

What are the actual results, why does no one ever post the results when the emissions fail to pass. The readings give very big clues to where the problem lies, this is diagnostic information, and without it, you are just speculating what is the fault with the car. There is nothing mysterious about emissions tests and their results. the readings are a result of a chemical reaction. what gois in, must come out. Understanding a little of basic chemistry and you can look at the readings and know whats happening. Catalytic converters ad another level to the chemistry, but again, what goes in comes out, all be it in a different form.

I will speculate that your results were High lambda reading with low HC and CO, almost zero infact. This is an indication of a leaking exhaust. If the HC and CO are indeed almost zero, there is absolutely nothing wrong with the cat and replacing it will not fix the problem. That is because the cat has reduced the CO into carbon and oxygen, and Coverted the HC into Hydrogen and Carbopn, juggling them all up to give CO2 and H2O. There are other oxides of nitrogen, but seeing as these are never measured, I wont dwell on it. TIf your HC and CO are almost zero, your cat is working as it it should.

All it needs is a small hole in the exhaust to draw in enough air, ( 20.9% oxygen) to give a vastly incorrect tailpipe lambda reading.

Check your exhasut from the manifold right the way to the tail pipe for signs of corrosion, especialy at the welds around the silencer. Not knowing iof this is a standard exhaust or a sports exhaust, I can only advise you to check the whole thing for leaks

[peekachoo]

What are the actual results, why does no one ever post the results when the emissions fail to pass. The readings give very big clues to where the problem lies, this is diagnostic information, and without it, you are just speculating what is the fault with the car. There is nothing mysterious about emissions tests and their results. the readings are a result of a chemical reaction. what gois in, must come out. Understanding a little of basic chemistry and you can look at the readings and know whats happening. Catalytic converters ad another level to the chemistry, but again, what goes in comes out, all be it in a different form.

I will speculate that your results were High lambda reading with low HC and CO, almost zero infact. This is an indication of a leaking exhaust. If the HC and CO are indeed almost zero, there is absolutely nothing wrong with the cat and replacing it will not fix the problem. That is because the cat has reduced the CO into carbon and oxygen, and Coverted the HC into Hydrogen and Carbopn, juggling them all up to give CO2 and H2O. There are other oxides of nitrogen, but seeing as these are never measured, I wont dwell on it. TIf your HC and CO are almost zero, your cat is working as it it should.

All it needs is a small hole in the exhaust to draw in enough air, ( 20.9% oxygen) to give a vastly incorrect tailpipe lambda reading.

Check your exhasut from the manifold right the way to the tail pipe for signs of corrosion, especialy at the welds around the silencer. Not knowing iof this is a standard exhaust or a sports exhaust, I can only advise you to check the whole thing for leaks

Fast idle test
CO 0.01% (pass)
HC 16ppm (pass)
Lambda 1.13 (fail)

2nd Fast idle test
CO 0.01% (pass)
HC 9 ppm (pass)
Lambda 1.11 (fail)

Natural Idle test
CO 0.05% (pass)


The car is a 1994 Mini 35 with an HIF 38 carb.

Edited by peekachoo, 28 August 2008 - 06:08 AM.

[peekachoo]

My car passed it's MOT today !!

I don't know what they did to get the emissions right but I haven't been charged for any new parts.

[NETTY]

My car passed it's MOT today !!

I don't know what they did to get the emissions right but I haven't been charged for any new parts.

our car passed today too!!! yay!