co2 levels
 

Hi, I have a 1998 V70, 2.5, 20v auto, non turbo. Last October a new aftermarket cat was fitted together with a new lambda.Since then I have covered 3,000 miles.
Car went in for itv [ mot ] today and failed on co2 levels at idle and 2500rpm.The readings are a fraction low and lambda is slightly high.
My mechanic and the itv tester checked to see if any codes came up but there were none.
Readings were taken of the cat which came up 0.00% and lambda 1,110%.
Last year cat readings 0,14% and lambda 1,001%
Both mechanic and tester are of the opinion that the cat is at fault. Granted it is a cheap ebay purchase but none the less I would expect it to last a few years. I purchased from a reputable parts company from the uk.
I would very much appreciate opinions please. thanks jack.

My experience with a cheap ebay cat was not very good.

When I had my previous V40 1997 2.0lt petrol non -turbo, so similar to your engine, just one less cylinder, I replaced the cat as the casing was damaged. Prior to replacement the car had always sailed through the MOT without any emissions problems -took it for the MOT and the tester had to rev the engine for far longer than previously and far faster to get the emissions within tolerance. I stood listening to the pistons screaming up the walls and thinking, that is going to self destruct soon. It got through the test, but it was not good.

I then found a secondhand genuine Volvo cat on ebay and decided to take a risk with that. Following year at the MOT it sailed through on emissions and at a mileage of about 280,000mls. The car continued with the same cat until I scrapped it at 370,000mls without any emissions issues.

The MOT tester is the same chappie who has tested all my cars for the last 20 years or so, so is known to me. He commented that folks who sell these cheap cats should be locked up as they are never any good.

Hi ITSv40, many thanks for that. Old Volvos are few and far between over here so little chance of picking one up from a breakers. A second hand one from ebay is certainly worth a look. By chance have you purchased a new cat at a reasonable price and if so can you recall the make. thanks jack.

Hi, I have done some research and have found reference to an oxygen sensor. Is it possible that if this is faulty it could give poor co2 readings which could be confused with a knackered cat. I would appreciate views please. thanks jack.

Just in the interests of accuracy, surely you are talking about CO levels, not CO2. CO2 and water are the normal products of combustion on a correctly running engine, it's CO that is undesirable as it indicates incomplete combustion and is poisonous.

Call me picky if you like...... :teeth_smile:

Agree with the comments above on very poor quality after-market cats. It's possible that it could be the oxygen sensor, but an incorrectly reading one is more likely to give a fault code, which it would seem you don't have.

Lambda reading your getting isn't the cat at fault, 0.00% is as good as it gets.
It's showing a bit lean which could simply be an air leak.
Is the exhaust gas tight at all the joints ? a slight leak at a joint could cause that reading
Are all the vacuum pipes in good order ? only takes a split in one to make a difference and not be bad enough to bring on a management light.
Did you fit a decent quality sensor ? e.g. not a cheapy universal one
Maf out of calibration can start to give incorrect lambda readings, although normally your long term fuel trims would show this.

No, never had to purchase a cat other than the one I replaced due to the outer covering being damaged. My fault going down a rough track and caught a sharp solid boulder.

I was just relaying my experience as the car previously had sailed through the mot. I changed the cat for a cheap one - cannot remember how much I paid for it, but it may have been about £100 or so, several years ago - and the first Mot afterwards the car really struggled to pass. The next mot - after fitting the second hand Volvo cat - the car sailed through. Nothing else was changed apart from routine servicing.

I hope you get yours sorted :)

Hi guys, thank you all for your info. You are right Luxobage, the paperwork from the test shows co and not co2.
I purchased the cat in October last year for £63.00 from online automotive in the uk. The lambda is bosch and cost £65.00.Looking at cat prices again I realise that I must have purchased the cheapest cat imagineable. Anyway my mechanic put my car on the hoist and checked all the joints from manifold to the tail pipe and there are no leaks.
This maybe totally irrelevant but a new silencer, cat and lambda were fitted in October of last year and it sailed through the itv [ mot ]. Due to the silencer being noisey I fitted an additional silencer on the tail pipe. Could that now be effecting the co readings.
Also I need to fit a new temperature sensor; could that have any bearing on co levels. I am sure these questions are stupid but I simply have no idea.
Since fitting the rear silencer the power is down very slightly but other than that the car is fine; save the fan is running a lot due to the faulty temp sensor.
both the mechanic and itv tester think the problem is a faulty cat but even at £63.00 I would have hoped for a few years of service.
Before the temp sensor packed up the car ran like a dream. smooth tick over
and acceleration and fuel consumption around 35 mpg.[ auto ]
I would very much appreciate any further views please. thanks jack

Jack,

Before you do anything else, change the faulty temp sensor.

The engine management system picks up signals from all manner of sources and uses that info to work out the optimum fuelling, ignition timing etc, and controls the engine to ensure best running. Duff info from a faulty sensor will throw that process out and the engine will never run well.

Hi ITSv40, that sounds a very good idea. I need to eliminate possible faults step by step. I thought it might be the oxygen sensor but none of the symptoms are present on my car. There does not appear to be any leaks. Should the temp sensor not rectify the fault I am left with the cat. however Byootox says 0.00% from the cat is as good as it gets. There are no codes showing.
I have thought about removing the tail silencer and then take it through the test again. I have no idea whether this will make any difference but it passed itv last year without it. Should it pass I can bolt it back on again.
I would very much welcome any other ideas. thanks jack.