MOT Failure - Advice Needed

[BilalSheikh]

Went for an MOT test on Saturday and it failed emissions. I was stumped as last year it performed really well. It was way below the figures.

I drive 60-70 miles everyday and the car was driven upto the rev limiter briefly before the mot to clear any deposits.

I had the CAT changed last year by Grays. I dont know whether that has anything to do with it. Plus i have K&N Filter installed.

Following are the results

NATURAL IDLE TEST
CO=.469% PASS

FAST IDLE TEST
CO=.605% FAIL
HC=93ppm PASS
Lambda=1.070 FAIL

SECOND FAST IDLE TEST
CO=.745% FAIL
HC=140ppm PASS
Lambda=1.063 FAIL

They have asked me to get the Lambda and CAT changed. I cant believe it as it has only just over a year i have had the CAT changed. I do note however i am having to top up the oil by about a litre or so once a month.

Please advice.

 

[bouncer]

Lambda is the clue here. . . . . . . Lambda is the air / fuel ratio
Suggests an air leak to me

Extra oxygen is being detected by the lambda sensor and is throwing more fuel in to compensate.

Have a look for holes in the exhaust or failed gaskets / seals
If there is a flexi before the cat check that its not got any cracks or splits in it.

Lambda is the clue here!!!!



sTeVe

 

[BilalSheikh]

You are spot on. Just popped into Kwick Fit and they said the exhaust is blowing at the joint between CAT and the Tail Pipe. I saw it myself.

Seems like Mr. Clutch didnt check that and wanted me to get the CAT and the Lambda changed. How can they skip that in the MOT? What a rip off.

Just out of curiosity. They didnt find lambda anywhere under the car from the CAT to the tail. Where is the lambda for my car and is that worth replacing as well.

What else should i do to make sure the car passes on the recheck. Is it common to topup 1 litre every say 2-3000 miles?

Thanks in advance.

 

[bouncer]

Was the Lambda sensor changed at the same time you got the cat last time?

Lambda sensors are prone to getting "Lazy" they are prone to carbon build up and heat stress, they still work albeit more slowly so sometimes they don't get picked up in diagnosis.
Lambda sensors work in a harsh environments and do need to be changed, just like spark plugs they have a limited life.
If you have never changed the lambda. . . . then its worth doing, could save you 15% a year on fuel.

As for the usage of oil, how olds is the car, is the compression good, is it serviced regular, does it have a oil leak or is it being used by the engine.
A little oil used by worn/ broken rings will increase the HC a little, but if you said it flew past the Emissions test last year then I wouldn't be too concerned about that.

Its down to how long it been running in the rich condition. CO 0.7 (is over fuelling,) and the cat can only withstand a certain amount of running rich before it becomes inefficient.

Cheapest option is fix the air leak and try a new lambda sensor.


sTeVe

 

[BilalSheikh]

Thanks Steve.

Much appreciated. The car is of 1995. It sailed past last time without needing anything apart from front brake pads changed.

When i got the CAT changed last they didnt change the lambda. I have seen the pictures online but when Kwick Fit took me under the car and showed me around there was no Lambda there. I did see blowing joint though.

Do you have any experience of pre face life w202. If so do you know where lambda is. I have searched on this forum and on google but didnt find any details or diagrams. I do know people here have access to details.ru site i hope some one can guide me. I just need to make sure Grays didnt just put a non compatible CAT on and took the lambda off and chucked it. As Kwick Fit pointed out this is a rare joint which is between the CAT and the Tail.

 

[Smatt]

Was the Lambda sensor changed at the same time you got the cat last time?

Lambda sensors are prone to getting "Lazy" they are prone to carbon build up and heat stress, they still work albeit more slowly so sometimes they don't get picked up in diagnosis.
Lambda sensors work in a harsh environments and do need to be changed, just like spark plugs they have a limited life.
If you have never changed the lambda. . . . then its worth doing, could save you 15% a year on fuel.

As for the usage of oil, how olds is the car, is the compression good, is it serviced regular, does it have a oil leak or is it being used by the engine.
A little oil used by worn/ broken rings will increase the HC a little, but if you said it flew past the Emissions test last year then I wouldn't be too concerned about that.

Its down to how long it been running in the rich condition. CO 0.7 (is over fuelling,) and the cat can only withstand a certain amount of running rich before it becomes inefficient.

Cheapest option is fix the air leak and try a new lambda sensor.


sTeVe

Hi bouncer,
In view of your comments above, would you recommend changing lambda on a 5yr old car with 60K on clock, if all emissions tests are fine?
Thanks, Matt

 

[nick mercedes]

Thanks Steve.

Much appreciated. The car is of 1995. It sailed past last time without needing anything apart from front brake pads changed.

When i got the CAT changed last they didnt change the lambda. I have seen the pictures online but when Kwick Fit took me under the car and showed me around there was no Lambda there. I did see blowing joint though.

Do you have any experience of pre face life w202. If so do you know where lambda is. I have searched on this forum and on google but didnt find any details or diagrams. I do know people here have access to details.ru site i hope some one can guide me. I just need to make sure Grays didnt just put a non compatible CAT on and took the lambda off and chucked it. As Kwick Fit pointed out this is a rare joint which is between the CAT and the Tail.

Lambas on the manifold?

 

[bouncer]

Hi bouncer,
In view of your comments above, would you recommend changing lambda on a 5yr old car with 60K on clock, if all emissions tests are fine?
Thanks, Matt

That is a good question, I would say that depends on a few factors:-

1) Driving trends, short journeys are not good for the lambda sensor or the cat, they never get up to a good working temperature.
2) Has the vehicle ever had emissions problems in the past?

I would say if your vehicle is serviced regular and never had an emissions or engine management fault then 85k shouldn't be a issue.

If you dive 5mins to work every day or the old lady who only drives to the local shop and back for a tin of cat food, then the service life of the sensor will be reduced to around 35k - 40k or worse.

You can not clean lambda sensors once they become contaminated or Lazy they stay that way, I had one guy tell me he dips them in diet coke and refits them!!!!!

You would be quite surprised the difference once you change a lazy sensor for a new one and you would be saving money on fuel.:bannana:


sTeVe

 

[maddog]

Lambda sensors are pretty much service items Nissan suggest to change them every 60,000 or 5 years if i was fitting a new cat i would also change the lambda as a matter of course as a faulty lambda could knacker the cat .

I've used these guys in the past

http://www.lambdasensor.com/

 

[kwakdonut]

Lambda sensor normally situated in the exhaust manifold or downpipe - the nearer the engine, the better is normal rule of thumb...

 

[BilalSheikh]

Thanks a lot guys.

Do you reckon i should remove the K&N and fit an OEM air filter for the recheck on MOT? As excessive air may be raising the emissions as well.

I will be fitting brand new plugs and changing the oil before taking it to the retest.

Could anyone tell me how to check the compression on the cylinders as i want to find out if there is a problem with one of the cylinders.

Last year i was in London and used to drive to work about 6 miles away. Now that i have moved out of London i drive to London every day. Mileage has increased but i never had to topup oil between changes ever before.

 

[bouncer]

Yes. . . channge the filter back to standard!

New plugs and oil. . . . always a good move.

As for compession testing. . . find your local independent let them do it.

Is it a leak or is the oild being used by the engine?

sTeVe

 

[Leemc2008]

Take off that cone filter.. get standard airbox back on..

Made my car fail emmissions as well!

 

[BilalSheikh]

Thanks

I will put the standard one on. There is no leak by the way. I dont think it is used by the engine as well as the car never smokes.

I do note that every time I disconnect the hose to throttle body there is fair amount of oil there. It seems it is passing from the engine to the throttle body through that small pipe which is I think called the breather. What does that indicate?

LEEMC2008 >> I don't have cone fitted it is a K&N filter only in the standard air box. I just wanted some umph thats why. I will do that. Does it affect the mpg as well?

 

[sweeper]

Went for an MOT test on Saturday and it failed emissions. I was stumped as last year it performed really well. It was way below the figures.

I drive 60-70 miles everyday and the car was driven upto the rev limiter briefly before the mot to clear any deposits.

I had the CAT changed last year by Grays. I dont know whether that has anything to do with it. Plus i have K&N Filter installed.

Following are the results

NATURAL IDLE TEST
CO=.469% PASS

FAST IDLE TEST
CO=.605% FAIL
HC=93ppm PASS
Lambda=1.070 FAIL

SECOND FAST IDLE TEST
CO=.745% FAIL
HC=140ppm PASS
Lambda=1.063 FAIL

They have asked me to get the Lambda and CAT changed. I cant believe it as it has only just over a year i have had the CAT changed. I do note however i am having to top up the oil by about a litre or so once a month.

Please advice.

The mot people should only advise you that the car has failed due to emmissions outside of the limits, it is not their place to tell you what to change, after all a proper diagnosis has to be made, you may change the lambda and cat only to find a faulty spark plug is causing the problem.

 

[BilalSheikh]

The mot people should only advise you that the car has failed due to emmissions outside of the limits, it is not their place to tell you what to change, after all a proper diagnosis has to be made, you may change the lambda and cat only to find a faulty spark plug is causing the problem.

I understand but shouldnt they be inspecting the exhaust. Also if they can ask me to get the CAT and Lambda changed from them with a bill close to £600, I am sure you would agree with me they should have told the actual problem of the blow.

 

[grober]

The lambda is on the upper side of the exhaust manifold and is easily seen by lifting the bonnet. It normally protrudes thro the metal heat shield which you may have to remove to get at it properly. Be very carefull not to disturb any other engine wiring nearby since the insulation can get brittle with age. 1995?

 

[kwakdonut]

Matter of interest - when was the last time it was serviced?

I always MOT after a recent service - less likely to fail on daft things that way!

 

[bouncer]

Small bit of advice. . . . lambda sensors are sometimes quite hard to get out
Its much easier to remove them when the car engine is cold.


sTeVe

 

[vijilants]

If you are going to replace the Lambda sensor, buy an OEM unit if you are planning on keeping the car. The aftermarket ones never tend to last very long.