Nct failure on high emissions

Chad111

I had my nct last week and failed on high emissions.

Low idle co 0.09 vol% pass
Lambda 0.98 pass
High idle co 0.66 vol % FAIL

I PUT DIPTANE and drove it hard. Put another bottle and did italian tune up on motorway before test. Reached at test centre and car went for nct straightaway.

Now high idle co is 0.42% . Still fail as it's above 0.20. Please suggest the reason of high emissions and way out.

I'll be grateful

Stoolbend

Like every other thread on emissions.

Make, model and engine size?

Looks like cat but who knows.

Chad111

Stoolbend wrote: »

Like every other thread on emissions.

Make, model and engine size?

Looks like cat but who knows.

Ford focus 1.4 lx petrol. 2005 . 150 k
Changed cat about 6 months ago but from scrapyard.

Bmw123d

Chad111 wrote: »

Ford focus 1.4 lx petrol. 2005 . 150 k
Changed cat about 6 months ago but from scrapyard.

The cats give trouble on them all the time. So that could be ur problem. But I’ve defo changed a few lambda sensors on them down the years. In fairness being on hear is all well and good asking but without me doing me own or anyone else for that matter doing the checks. It’s all just guess work.

But my money is on either of what I’ve mentioned.

rex-x

The lambda reading is slightly rich which will increase the co reading but it shouldnt be an issue for a good cat. Unfortunately for you it really can only be your cat thats gone bad.

Chad111

rex-x wrote: »

The lambda reading is slightly rich which will increase the co reading but it shouldnt be an issue for a good cat. Unfortunately for you it really can only be your cat thats gone bad.

I have changed Cat In last Oct but it was used. Any advice for buying a good cat but not too dear. Already spent money on few things. What is universal cat?

Another thing I forgot to mention is that car is burning too much oil for the last few months. I couldn't find any whitish stuff in engine oil or coolant. Is it also because of cat or something else.

rex-x

Chad111 wrote: »

I have changed Cat In last Oct but it was used. Any advice for buying a good cat but not too dear. Already spent money on few things. What is universal cat?

Another thing I forgot to mention is that car is burning too much oil for the last few months. I couldn't find any whitish stuff in engine oil or coolant. Is it also because of cat or something else.

Get a low mile second hand genuine cat it's the only way. Don't go near universal ones

Chad111

rex-x wrote: »

Get a low mile second hand genuine cat it's the only way. Don't go near universal ones

Thank you for the reply. As you said cat is the only option so i will start looking. Had a bad experience last time.it was original n used but lasted for only 6 months. Should o only replace cat or sensors also.

Bmw123d

Chad111 wrote: »

Thank you for the reply. As you said cat is the only option so i will start looking. Had a bad experience last time.it was original n used but lasted for only 6 months. Should o only replace cat or sensors also.

Use the sensors that come in the replacement cat

Chad111

Bmw123d wrote: »

Use the sensors that come in the replacement cat

Went to a local garage today. He checked and changed the temp sensor today and said it would be fine for nct. He said there is no engine light and cat looks fine. Confused again

Bmw123d

Chad111 wrote: »

Went to a local garage today. He checked and changed the temp sensor today and said it would be fine for nct. He said there is no engine light and cat looks fine. Confused again

I did tell u the sensors from the start. And look it was done. I told u that any one that’s done abit with them focuses would know that them sensor do go. So I’d take his word on it and retest it.

Best of look

Chad111

Bmw123d wrote: »

I did tell u the sensors from the start. And look it was done. I told u that any one that’s done abit with them focuses would know that them sensor do go. So I’d take his word on it and retest it.

Best of look

Just an update.

Had nct today but failed again on emissions

High idle reading was 0.71 even higher than last time which was.0.42.

So ect sensor change is not the solution. Now Machanic is saying that changr 2nd lambda sensor. I think it hit and try situation here. As per his opinion cat would be last thing as there is no engine light on and readings are not that unusual.

Already had nct 3 times and still problem is not diagnosed.

rex-x

Chad111 wrote: »

Just an update.

Had nct today but failed again on emissions

High idle reading was 0.71 even higher than last time which was.0.42.

So ect sensor change is not the solution. Now Machanic is saying that changr 2nd lambda sensor. I think it hit and try situation here. As per his opinion cat would be last thing as there is no engine light on and readings are not that unusual.

Already had nct 3 times and still problem is not diagnosed.

The problem is the cat. The 2nd lambda sensor doesn't control the emissions so I don't know where he is going there! Get a good 2nd hand cat and use your original sensors and your problem will be gone
It was never the coolant sensor and never could have been from your readings.

Leonard Hofstadter

What are the HC emissions like? Is it burning oil? I note you haven't posted those readings. It probably is the cat, as previously mentioned, but it would be worth knowing the answers to the above.

The post-cat sensor is supposed to monitor the efficacy of the cat. It would have little to no affect on the running of the engine.

Chad111

captainspeed wrote: »

What are the HC emissions like? Is it burning oil? I note you haven't posted those readings. It probably is the cat, as previously mentioned, but it would be worth knowing the answers to the above.

The post-cat sensor is supposed to monitor the efficacy of the cat. It would have little to no affect on the running of the engine.

Reading at first nct.

Low idle co 0.09 vol% pass
Lambda 0.98 pass
High idle co 0.66 vol % FAIL

Then advised to put dipetane but failed again

Low idle and lambda same
High idle. 0.42 but fail

Then advised to change ect sensor but again failed

High idle 0.71 vol%

Now Machanic opinion is to change 2nd lambda sensor which will not change the emissions readings as explained by one of member. SO CAT LOOKS the only option. If knew earlier I wouldn't have wasted money on nct retests and labour/part charges.

Car is also being oil and you see a black carbon and water when cold start

crosshair1

As you've been told already, it needs a cat.
The lambda value is ok, on the richer side, 2 tests have confirmed that the air/fuel ratio is acceptable when testing - this suggests that the engine is running in closed loop and that all is in order on that side.
The co is ok at idle and failing at high idle - this is classic cat failure.
The test for this is to check the output from both o2 sensors and if sensor 2 is switching like 1 then the cat is not doing its job.
I would guess its about a 50/50 of getting a working one from a breakers.

Leonard Hofstadter

The only way the cat will really be fixed is by getting a new one. Since it's a Ford they can't be that expensive.

As they say, buy cheap buy twice.

You still haven't told us what the HC readings are. We've got the CO ones but not the HC.

If they're high it could be because the engine is worn out or burning copious quantities of oil - and a new cat won't fix that.

If it goes at least 600 miles or 1000 km on a litre of oil then oil consumption won't cause it to fail an emissions test.

Chad111

captainspeed wrote: »

The only way the cat will really be fixed is by getting a new one. Since it's a Ford they can't be that expensive.

As they say, buy cheap buy twice.

You still haven't told us what the HC readings are. We've got the CO ones but not the HC.

If they're high it could be because the engine is worn out or burning copious quantities of oil - and a new cat won't fix that.

If it goes at least 600 miles or 1000 km on a litre of oil then oil consumption won't cause it to fail an emissions test.

I understand but Machanic argument is that car is not loosing power , no rattling sound and no check engine lights on. As I don't wanted to spend much so took a chance. You are right that buying a cat from yard would be a chance again. I bought the cat about 6 months ago from yard it fails nct. Anyway as suggested o would have to go for another used cat and take a chance. Would you think that burning oil is also because of bad cat?

Is the cat same for 1.4 and 1.6 of 2005 focus

Thanks a million

rex-x

Chad111 wrote: »

I understand but Machanic argument is that car is not loosing power , no rattling sound and no check engine lights on. As I don't wanted to spend much so took a chance. You are right that buying a cat from yard would be a chance again. I bought the cat about 6 months ago from yard it fails nct. Anyway as suggested o would have to go for another used cat and take a chance. Would you think that burning oil is also because of bad cat?

Thanks a million

Your mechanic sounds like an idiot if that's his argument to be honest. He has no idea what he's doing

Chad111

captainspeed wrote: »

The only way the cat will really be fixed is by getting a new one. Since it's a Ford they can't be that expensive.

As they say, buy cheap buy twice.

You still haven't told us what the HC readings are. We've got the CO ones but not the HC.

If they're high it could be because the engine is worn out or burning copious quantities of oil - and a new cat won't fix that.

If it goes at least 600 miles or 1000 km on a litre of oil then oil consumption won't cause it to fail an emissions test.

Low idle co 0.09
(810)rpm HC 26 ppm

Lambda 0.98

High idle co 0.66
(3150)rpm HC 96ppm

Engine oil temp 83 c

Leonard Hofstadter

Chad111 wrote: »

I understand but Machanic argument is that car is not loosing power , no rattling sound and no check engine lights on. As I don't wanted to spend much so took a chance. You are right that buying a cat from yard would be a chance again. I bought the cat about 6 months ago from yard it fails nct. Anyway as suggested o would have to go for another used cat and take a chance. Would you think that burning oil is also because of bad cat?

Is the cat same for 1.4 and 1.6 of 2005 focus

Thanks a million

I don't know if they're the same, but I do know if you'd paid out for a new one in the beginning you wouldn't still be having problems with it.

Burning oil is nothing to do with a faulty cat - but sustained oil burning will shorten the life of a catalytic converter for sure and eventually wear it out.

As I mentioned previously, unless it's using more than a litre of oil every 600 miles or 1000 km, it's unlikely to be the cause of your problem.

I'm not familiar with Fords but many petrol engines do burn a bit of oil as they get older and it's fine once it's not more than the threshold I mentioned above.

The HC is fairly high at high idle (so it must be using some oil) although it's still well below the acceptable limit. My money is on it needing a new cat, as the others have mentioned.

Chad111

I am going to change used cat converter tom. I have been advised to drain the old oil and put 15w 40 before cat change. Does it make any difference for nct. I was using 5w30 earlier.

Anybody have an idea about 2005 1.4 ford focus cat change. Will it be simple fix or any welding invloved.

Thanks

rex-x

Chad111 wrote: »

I am going to change used cat converter tom. I have been advised to drain the old oil and put 15w 40 before cat change. Does it make any difference for nct. I was using 5w30 earlier.

Anybody have an idea about 2005 1.4 ford focus cat change. Will it be simple fix or any welding invloved.

Thanks

Put the correct oil in. Fords of that era take 5w30 semi synthetic not fully. You will probably only be able to get it in a motorfactors

tcawley29

rex-x wrote: »

Put the correct oil I'm. Fords of that era take 5w30 semi synthetic not fully. You will probably only be able to get it in a motorfactors

I thought with older engines you could put in a slightly thicker grade?

I remember in my corollas manual there was quite a few grades listed (depending on climate temperature).

I looked at the time as a dealer used 10w40 to service it and I thought it was supposed to get 5w30. Only difference I noticed was slightly better mpg when I did that. Not enough to be a big deal.

rex-x

tcawley29 wrote: »

I thought with older engines you could put in a slightly thicker grade?

I remember in my corollas manual there was quite a few grades listed (depending on climate temperature).

I looked at the time as a dealer used 10w40 to service it and I thought it was supposed to get 5w30. Only difference I noticed was slightly better mpg when I did that. Not enough to be a big deal.

Fords are fussy, they like their specific 5w30 semi synth oil (The only manufacturer I know of that uses it)

Leonard Hofstadter

tcawley29 wrote: »

I thought with older engines you could put in a slightly thicker grade?

I remember in my corollas manual there was quite a few grades listed (depending on climate temperature).

I looked at the time as a dealer used 10w40 to service it and I thought it was supposed to get 5w30. Only difference I noticed was slightly better mpg when I did that. Not enough to be a big deal.

Using 10W40 will use a little more fuel than 5W30. It also won't offer the same protection for the engine when it is cold.

The reason to go for thicker oil is when a car starts burning some, 10W40 will cut oil consumption down fairly handily compared to 5W30. Excess oil consumption will cause higher HC emissions and will damage the catalytic converter, O2 sensors etc.

If we had a hotter climate then yes thicker oil is necessary, otherwise the engine won't be properly protected when it's fully warmed up with all the heat, but 5W30 should be fine for most cars in this country.

tcawley29

captainspeed wrote: »

Using 10W40 will use a little more fuel than 5W30. It also won't offer the same protection for the engine when it is cold.

The reason to go for thicker oil is when a car starts burning some, 10W40 will cut oil consumption down fairly handily compared to 5W30. Excess oil consumption will cause higher HC emissions and will damage the catalytic converter, O2 sensors etc.

If we had a hotter climate then yes thicker oil is necessary, otherwise the engine won't be properly protected when it's fully warmed up with all the heat, but 5W30 should be fine for most cars in this country.

Yeah I had switched back to 5w30 myself as there was no issues with the car and it was the top recommended grade

standardg60

Chad111 wrote: »

I am going to change used cat converter tom. I have been advised to drain the old oil and put 15w 40 before cat change. Does it make any difference for nct. I was using 5w30 earlier.

Anybody have an idea about 2005 1.4 ford focus cat change. Will it be simple fix or any welding invloved.

Thanks

Everyone in the game advises to do that if the car is burning oil but if the piston rings are worn, which I suspect, it won't make a scintilla of difference.

You said the the cat was changed six months ago, was it for the same reason? eg. nct emissions fail? Just change the cat, I wouldn't bother with a new oem one unless you fix the source or you'll be replacing it every year anyway.

Either do the rings or just replace the car would be my advice.

Chad111

standardg60 wrote: »

Everyone in the game advises to do that if the car is burning oil but if the piston rings are worn, which I suspect, it won't make a scintilla of difference.

You said the the cat was changed six months ago, was it for the same reason? eg. nct emissions fail? Just change the cat, I wouldn't bother with a new oem one unless you fix the source or you'll be replacing it every year anyway.

Either do the rings or just replace the car would be my advice.

Changed the cat because of rattling sound. Had nct valid at that time.will be replacing cat tom and do the nct. Not happy with ford at all and will switch to toyota. Saw the old cat and flexi pipe is also broken. Not sure if it makes any difference. Already changed brakes serviced and I think it would be easy to sell with nct

Chad111

Chad111 wrote: »

Changed the cat because of rattling sound. Had nct valid at that time.will be replacing cat tom and do the nct. Not happy with ford at all and will switch to toyota. Saw the old cat and flexi pipe is also broken. Not sure if it makes any difference. Already changed brakes serviced and I think it would be easy to sell with nct

Replaced the catalytic converter 3 days ago. While replacing Machanic found oil leakage into cat and in his opinion it could be demaged engine seals. But he said if nct passed you drive it for few months and scrap it. I am going for nct in 2 days time. In my case should I go with hot engine temp or cold. Also should I use dipetane before test.

I hope not much oil is leaked in cat in a week time and nct test would be pass.

Leonard Hofstadter

Yes, the engine should be good and hot before it's tested. Turn up early and they'll test it straight away if it's not too busy, that again will help with it passing.

Depending on where the oil leaks are, it may not be expensive at all to fix (for example, a rocker cover gasket wouldn't cost much more than €100 to fix - certainly no more than €150 anyway - and that would cause oil to leak onto the catalytic converter depending on the engine) - and certainly not grounds to scrap a car that is otherwise running fine. You will probably get some sort of advisory or note on the NCT report telling you where the leaks are anyway if there really are oil leaks.

No, Diptane won't make any difference (except for lightening your wallet).

Chad111

I have different opinios from members. Changed sensors lambda and the finally cat. But still Nct failed for the 4th time with the same high emissions problem

Low idle and lambda pass
High idle 0.53% fail

Bit frustrated now. If anybody could please let me know what the real problem is. Also is there any garage in limerick who could really diagnose the real prob but not too dear as already spent too much.

TIA

Get rid of that ****ty mechanic before you do anything. Any time I bring my car to my mechanic he checks the emissions before I spend any money on it and he picks up a tool, this lad should have the equipment to measure the emissions instead of sending you off 4 times with his guessing that it will pass, ridiculous.

Chad111

Melissa Inexpensive Tray wrote: »

Get rid of that ****ty mechanic before you do anything. Any time I bring my car to my mechanic he checks the emissions before I spend any money on it and he picks up a tool, this lad should have the equipment to measure the emissions instead of sending you off 4 times with his guessing that it will pass, ridiculous.

So I should go to a garage who do the emissions test. Will they be able to diagnose the prob after emissions test. Some body told me a garage who does this test in 35 euros. But I am not sure do they tell you the exact solution or is it only readings you get.

If anybody knows any good Machanic in limerick who does this please suggest. I'll be grateful

rex-x

You still need a cat, was it second hand? I agree you should find a better mechanic though

standardg60

Chad111 wrote: »

Replaced the catalytic converter 3 days ago. While replacing Machanic found oil leakage into cat and in his opinion it could be demaged engine seals. But he said if nct passed you drive it for few months and scrap it. I am going for nct in 2 days time. In my case should I go with hot engine temp or cold. Also should I use dipetane before test.

I hope not much oil is leaked in cat in a week time and nct test would be pass.

This is more than likely what the problem is. Unfortunately the engine is burning too much oil for the cat to deal with.

Worn piston rings is the most likely reason (open to correction on this), and replacing them is a big job as both head and sump have to come off. The rings themselves could be the guts of 300 euro from ford, plus new head gasket, have no idea what a mechanic might charge as I did them myself, but I wouldn't expect much change from 500.

Chad111

Chad111 wrote: »

So I should go to a garage who do the emissions test. Will they be able to diagnose the prob after emissions test. Some body told me a garage who does this test in 35 euros. But I am not sure do they tell you the exact solution or is it only readings you get.

If anybody knows any good Machanic in limerick who does this please suggest. I'll be grateful

I don't live in limerick but any decent mechanic should have a machine to test emissions and not charge you for it if they use it while fixing a problem

As others have said sometimes emissions can be linked to the engine and can cost a fortune to fix so not worth it on old cars (which mine is hence why he tests it before I spend any money to get it through nct) and should have been done to yours

Chad111

Melissa Inexpensive Tray wrote: »

I don't live in limerick but any decent mechanic should have a machine to test emissions and not charge you for it if they use it while fixing a problem

As others have said sometimes emissions can be linked to the engine and can cost a fortune to fix so not worth it on old cars (which mine is hence why he tests it before I spend any money to get it through nct) and should have been done to

Chad111

Went to garage today for emissions test. He confirmed no air leaks or problems other than cat. Readings were still high 0.53 % vol on high idle.pre cat sensor readings are ok but Post cat sensor readings were not static. So according to him it's cat failure. Any suggestions on this plus any cheap place to buy new cat. Thanks

Tea drinker

Can you get refund on old cat? That will make replacing it a lot cheaper...

Chad111

Just an update. Went to buy a new cat today and after looking at my nct reports his opinion is not to buy a new cat. He is one of the most experienced guy for exhaust and cats.

He said that there is something else going on
As after even changing used cat there is not much difference. Co readings are up on high idle which means air fuel ratio is not perfect and readings are high because of unburnt fuel.he suggested to change the original ford spark plugs because ngk plugs sometimes make trouble in ford's. He also advised to crecheck any air leaks which BTW I had tested earlier.

Now my questions are where I can do pre nct test for free for air leaks. Someone mentioned in other thread but couldn't find it. Secondly any advice on plug change and how to check gaps.

Thanks

rex-x

Chad111 wrote: »

Just an update. Went to buy a new cat today and after looking at my nct reports his opinion is not to buy a new cat. He is one of the most experienced guy for exhaust and cats.

He said that there is something else going on
As after even changing used cat there is not much difference. Co readings are up on high idle which means air fuel ratio is not perfect and readings are high because of unburnt fuel.he suggested to change the original ford spark plugs because ngk plugs sometimes make trouble in ford's. He also advised to crecheck any air leaks which BTW I had tested earlier.

Now my questions are where I can do pre nct test for free for air leaks. Someone mentioned in other thread but couldn't find it. Secondly any advice on plug change and how to check gaps.

Thanks

Genuine plugs are a must in a ford engine like that but not for your issue. Your lambda reading is showing there is no issue (very slightly rich) with the air fuel ratio so therefore it must be the cat. The cat can be tested for function by measuring its temp while at high idle. It should be hotter on the outlet than the inlet (side closer to the engine)

Skatedude

So Have you actually changed the cat or not? Or is still the one you got from the scrap yard which was never tested good?

dreamer001

Melissa Inexpensive Tray wrote: »

Get rid of that ****ty mechanic before you do anything. Any time I bring my car to my mechanic he checks the emissions before I spend any money on it and he picks up a tool, this lad should have the equipment to measure the emissions instead of sending you off 4 times with his guessing that it will pass, ridiculous.

can tell me garage name and number please?

Chad111

Skatedude wrote: »

So Have you actually changed the cat or not? Or is still the one you got from the scrap yard which was never tested good?

No I didn't change as the guy who sells cat is saying it wouldn't make much difference.

Chad111

dreamer001 wrote: »

can tell me garage name and number please?

I think can't share names and numbers but he is on ballysimon road business park who deals in exhaust and cats.

John.G

Chad111 wrote: »

Just an update. Went to buy a new cat today and after looking at my nct reports his opinion is not to buy a new cat. He is one of the most experienced guy for exhaust and cats.

He said that there is something else going on
As after even changing used cat there is not much difference. Co readings are up on high idle which means air fuel ratio is not perfect and readings are high because of unburnt fuel.he suggested to change the original ford spark plugs because ngk plugs sometimes make trouble in ford's. He also advised to crecheck any air leaks which BTW I had tested earlier.

Now my questions are where I can do pre nct test for free for air leaks. Someone mentioned in other thread but couldn't find it. Secondly any advice on plug change and how to check gaps.

Thanks

"He said that there is something else going on"
I would venture that he is probably correct.

One of the items that I've noticed is that in every one of your (NCT) tests, the Lambda has never been at 1.0 or slightly higher, I can state quite categorically here that in at least 4 cars (all VW) in my family at one time or another that every one of them NEVER had a Lambda reading of < 1.0, (and passed the test) generally they would be in the order of 1.0, 1.005,1.01. and as has been stated above low Lambda means increasd CO.
It goes without without saying that the single most important bearing on combustion efficiency is/are the spark plugs and I would suggest changing them as close to the NCT as possible.

Regarding air leaks: In older cars, the air leak can occur due to a corroding exhaust box and even though the Lambda reading as seen by the ECU may be correct it will show up as a high reading on the NCT as they have the probe in the exhaust pipe and can also result in REDUCED CO & HC due to the air dilution as measured at the exhaust pipe. It would be a nice trick to just have enough of a air leak to reduce the CO & the HC but still not exceed the Lambda high limit!!.
In view of the above, (and your low Lambda reading), IMO only, I would think that you probably havn't got any air leakage.

I will edit this post and include the NCT emission tests with/without a "holed" rear exhaust box.

Edit: here are the readings...before & after rear box was renewed.

Date 23/11/2015
Miles 177,466
Oil Temp 82 Deg C
Low Idle 720 RPM
CO 0.04 %
HC 21 PPM
High Idle 3200 RPM
Lambda 1.1 FAIL
CO 0.04 %
HC 22 PPM

Date 26/11/2015
Miles 177,741
Oil Temp 82 Deg C
Low Idle 760 RPM
CO 0.15 %
HC 180 PPM
High Idle 2940 RPM
Lambda 1.01
CO 0.21 %
HC 142 PPM

Regarding (again) Spark plugs and rereading your post above, I would forget about the gap, just go away and buy a new set of plugs and install them. In my case, I just buy the cheapest recommended ones for my cars for around €20 or so and install them on the morning of the NCT and renew them every year, the above car has in excess of 200K miles up now and the oil consumption is around 750 miles/1200 Kms/Litre.
I fully accept that different makes of cars have differences but even with "excessive" oil consumption, it is relatively easy to pass the NCT. Again, for reference only here is the last emission tests for one of those cars. The only reason that I am going on a bit is that High CO is almost entirely dependent on combustion efficiency and oil burning doesn't have a huge effect on it...its the high HC that will eventually kill you/me before the CO does.

Date 07/11/2017
Miles 199,801
Oil Temp 2 Deg C
Low Idle 760 RPM
CO 0.16 %
HC 153 PPM
High Idle 3090 RPM
Lambda 1.02
CO 0.17 %
HC 141 PPM

Chad111

John.G wrote: »

"He said that there is something else going on"
I would venture that he is probably correct.

One of the items that I've noticed is that in every one of your (NCT) tests, the Lambda has never been at 1.0 or slightly higher, I can state quite categorically here that in at least 4 cars (all VW) in my family at one time or another that every one of them NEVER had a Lambda reading of < 1.0, (and passed the test) generally they would be in the order of 1.0, 1.005,1.01. and as has been stated above low Lambda means increasd CO.
It goes without without saying that the single most important bearing on combustion efficiency is/are the spark plugs and I would suggest changing them as close to the NCT as possible.

Regarding air leaks: In older cars, the air leak can occur due to a corroding exhaust box and even though the Lambda reading as seen by the ECU may be correct it will show up as a high reading on the NCT as they have the probe in the exhaust pipe and can also result in REDUCED CO & HC due to the air dilution as measured at the exhaust pipe. It would be a nice trick to just have enough of a air leak to reduce the CO & the HC but still not exceed the Lambda high limit!!.
In view of the above, (and your low Lambda reading), IMO only, I would think that you probably havn't got any air leakage.

I will edit this post and include the NCT emission tests with/without a "holed" rear exhaust box.

Edit: here are the readings...before & after rear box was renewed.

Date 23/11/2015
Miles 177,466
Oil Temp 82 Deg C
Low Idle 720 RPM
CO 0.04 %
HC 21 PPM
High Idle 3200 RPM
Lambda 1.1 FAIL
CO 0.04 %
HC 22 PPM

Date 26/11/2015
Miles 177,741
Oil Temp 82 Deg C
Low Idle 760 RPM
CO 0.15 %
HC 180 PPM
High Idle 2940 RPM
Lambda 1.01
CO 0.21 %
HC 142 PPM

Regarding (again) Spark plugs and rereading your post above, I would forget about the gap, just go away and buy a new set of plugs and install them. In my case, I just buy the cheapest recommended ones for my cars for around €20 or so and install them on the morning of the NCT and renew them every year, the above car has in excess of 200K miles up now and the oil consumption is around 750 miles/1200 Kms/Litre.
I fully accept that different makes of cars have differences but even with "excessive" oil consumption, it is relatively easy to pass the NCT. Again, for reference only here is the last emission tests for one of those cars. The only reason that I am going on a bit is that High CO is almost entirely dependent on combustion efficiency and oil burning doesn't have a huge effect on it...its the high HC that will eventually kill you/me before the CO does.

Date 07/11/2017
Miles 199,801
Oil Temp 2 Deg C
Low Idle 760 RPM
CO 0.16 %
HC 153 PPM
High Idle 3090 RPM
Lambda 1.02
CO 0.17 %
HC 141 PPM

He pointed out the exact same issue and also noted that all my lambda readings are below 1.0. That's why he advised me to use the ford genuine spark plugs. I got them now and would change just before nct. I am also planning to change the oil to 5w30 as my other Machanic put 10w40 in last service + use cat clean before nct. What do you think that changing spark plugs would improve lambda reading or should I also change lambda.? In obd diagnosis sensors were working fine though.

Thanks

John.G

Chad111 wrote: »

He pointed out the exact same issue and also noted that all my lambda readings are below 1.0. That's why he advised me to use the ford genuine spark plugs. I got them now and would change just before nct. I am also planning to change the oil to 5w30 as my other Machanic put 10w40 in last service + use cat clean before nct. What do you think that changing spark plugs would improve lambda reading or should I also change lambda.? In obd diagnosis sensors were working fine though.

Thanks

I would just renew the plugs now only as a retest is "only" €28 or so, and take it step by step, a new O2 sensor is probably > €150. I am not quite clear on this but were the NGK plugs installed since your problems began? or more simply put, how long are the present plugs installed??.

I also clean the throttle body on my cars before the NCT, if the throttle plate is sticking a little then the ECU will also advance the ignition timing to maintain the idling speed, advanced timing results in increased CO, all I do is remove the air cleaner and squirt a drop of WD40 or carbon cleaner If you have got it onto the throttle plate with engine stopped and just allow it to soak for a few minutes before restarting.

OBD diagnostics: in general I would think that they give a reasonably accurate picture of whats happening.
Long long before any of this I used to just stick a needle on the end of my multimeter probe into the O2 sensor wire and see it the voltage was fluctuating rapidly, if it was, you were OK.

Changing the oil: I dont think this will have any effect.

Also the theory of having the engine at full working temperature....I am a little skeptical of this myself as any oil will be thinner at full operating temperature and thus has a easier pathway to the combustion chamber(s). I tend to drive the 4 miles or so to the test centre from cold and the test is then done with a slightly warm engine but certainly not "hot".

Chad111

John.G wrote: »

I would just renew the plugs now only as a retest is "only" €28 or so, and take it step by step, a new O2 sensor is probably > €150. I am not quite clear on this but were the NGK plugs installed since your problems began? or more simply put, how long are the present plugs installed??.

I also clean the throttle body on my cars before the NCT, if the throttle plate is sticking a little then the ECU will also advance the ignition timing to maintain the idling speed, advanced timing results in increased CO, all I do is remove the air cleaner and squirt a drop of WD40 or carbon cleaner If you have got it onto the throttle plate with engine stopped and just allow it to soak for a few minutes before restarting.

OBD diagnostics: in general I would think that they give a reasonably accurate picture of whats happening.
Long long before any of this I used to just stick a needle on the end of my multimeter probe into the O2 sensor wire and see it the voltage was fluctuating rapidly, if it was, you were OK.

Changing the oil: I dont think this will have any effect.

Also the theory of having the engine at full working temperature....I am a little skeptical of this myself as any oil will be thinner at full operating temperature and thus has a easier pathway to the combustion chamber(s). I tend to drive the 4 miles or so to the test centre from cold and the test is then done with a slightly warm engine but certainly not "hot".

I have checked the plugs today and they are all oily. I think there is some internal oil leakage which is also causing high emissions. So I guess there is no point of buying a new cat.
I am going to replace the plugs and use a cat clean and will try for nct for the last time. If not passed I'll be braking it.

John.G

Chad111 wrote: »

I have checked the plugs today and they are all oily. I think there is some internal oil leakage which is also causing high emissions. So I guess there is no point of buying a new cat.
I am going to replace the plugs and use a cat clean and will try for nct for the last time. If not passed I'll be braking it.

On alot of cars oil will leak from the rocker gasket into the plug wells but it doesnt reach the plug itself and isnt a problem as long as it doesnt build up and enter the plug lead boots, I just clean mine out occasionally. (it only builds up around No3)

Best of luck with the test and remember, if possible dont replace the plugs until right before the test, easily done if you are carrying it out yourself. John