Failed mot due to high co. Cat or lambda to blame?

[`state]

Took my mums astra mk4 for mot today. Failed on high co. Asked the guy at the garage but he said he had no idea what would be causing it,great. Car runs really well.Is regularly serviced and returns good mpg.
Emission test results were fast idle test failed co 0.69 limit 0.3. second fast idle test failed co 0.69 limit 0.3. and natural idle test failed 0.67 limit 0.5.
So does this look like a dodgy lambda or a knackered cat? Would a tin of cat cleaner bring it down enough?
Thanks in advance for any help.

[joem83]

Give it a jolly good thrashing and take it straight in for the emissions.

Chances are the cat doesnt get very hot when your mum drives it

[slammage]

as above give it a good spirited run down some dual carriageways, and go straight in, some cat cleaner wouldn't do any more harm either.

[`state]

I took it in and ive had it afew days now and i don't hang about! I'm just getting her to check the receipt for the exhaust she had fitted about 6 months ago as I'm wondering if they fitted a cheapo cat that isnt bringing it down enough.

[tineca]

Drop a bottle of cataclean in an do 70 in third. Retest straight away. Should be fine

[Battles]

Italian tune up.
Surprised the MOT guy didn't suggest it, I've heard of a few people being told that especially if the emmissions are the only issue with the car.

[omega]

my mrs206 failed on the same i had but a cheap cat on it 6 months ago replaced cat and it passed.but mot place told me it was the cat.

[Bozwell]

need to see what the rest of the exhaust emmisions are to tell what may possibly be wrong

if Lambda reading is 1.0 then it's probably the cat as the mixture is a perfect Lambda. a higher than 1 reading is a weak mixture and less than 1 is a rich mixture.

a slightly rich mixture will not catalize properly hence a bit of CO not being converted into CO2 and water. you would also see slightly higher HCs but probably not enough to go over the limit for the test.

[Mantasport]

One of the reasons i use an MOT station out of town is to give each car i take a run to warm the cat up, and if the owner doesn't use the rev range normally it gets an Italian tune up on the way.

Big problem with a lot of MOT stations is if you drop the car off and leave it all day the cat will never be up to full working temp when they test it, so if everything isn't spot on the emissions will fail
Infact sometimes even if everything is ok it will still fail the first test, and require the 2nd test that has the operator hold the revs around 3000rpm for 3 minutes to warm the cat first.
Worth booking an MOT and driving the car there at the test time, plus take the long way around not in stop start traffic with open roads and medium to high revs to get the cat fully warm

[ChasR]

Jan 10, 2015 8:58:18 GMT Mantasport said:

One of the reasons i use an MOT station out of town is to give each car i take a run to warm the cat up, and if the owner doesn't use the rev range normally it gets an Italian tune up on the way.

Big problem with a lot of MOT stations is if you drop the car off and leave it all day the cat will never be up to full working temp when they test it, so if everything isn't spot on the emissions will fail
Infact sometimes even if everything is ok it will still fail the first test, and require the 2nd test that has the operator hold the revs around 3000rpm for 3 minutes to warm the cat first.
Worth booking an MOT and driving the car there at the test time, plus take the long way around not in stop start traffic with open roads and medium to high revs to get the cat fully warm

What he said . I am lucky enough to know a great MOT tester but sometimes that choice is not available.

My sister's Mondeo was failing the emmissions as the car was started up from cold. After warming the engine up it sailed through the emissions with the engine going from a failure to something which barely registered on his machine in terms of the CO and HC.

On the basis your lambda reading seems to be OK I would say that you fuel mixture is OK. However the CO would suggest something is making things rich.

Either the car was not warm when it was tested, a sensor is iffy (like a coolant temperature sensor (unlikely) or the cat has had its day. Despite what some say I have never been able to pass a pattern cat through an MOT despite ragging the car hard and so on. This has happened to me on 2 occasions now. After a genuine cat was sourced for one of the cars the emissions came right into line .

[mattrb]

Is it the X16SZR engine by any chance? 1.6 8v single point injection if you're not sure of engine codes. If so I wouldn't rule out an exhaust leak at the manifold/ down pipe connection before you start changing things. It can be quite subtle.

Edit: To explain a bit more. The blowing at said interface can be really minor or non-existent at tickover. Increasing revs a little (possible on the x16szr whilst under the bonnet) will often reveal a definite leak. Poor design is to blame but a good clean of the mating faces, a new ring gasket and a pair of studs and nuts will probably cure it. Don't avoid replacing the studs and nuts if yours are in anyway suspect.

If your lambda reading is within limits (printout?) then it's almost certainly ok. I suspect you have either a cheapo cat (euro cat?), a leak on the exhaust or both.

If you have an infrared temp gauge (ebay <20 quid) you can get a decent indication of if the cat is doing its job. I forget the recommended minimum temp advised to me but I'm sure a Google search will help.

Cataclean is useless in my experience as are euro cats and non-approved cats regardless of applicability to your vehicle age.

[mattrb]

Just re-read this and to add to this even more; high CO indicates a rich mixture. A leak at the gasket joint I indicated in my earlier post will affect the lambda reading, causing the ECU to believe the mixture to be lean. This is then compensated by the ECU adjusting the signal to the ICV and coilpack, resulting in an engine that runs pretty well and idles more or less as it should, just as you describe. I'll bet there is a slight hesitancy as the throttle begins to be applied, barely detectable sometimes.

I remembered a bit more about checking the cat, input temp Immediately before the cat should be around 200deg C once settled iirc. The exit temp, immediately after should be much higher otherwise the cat isn't doing anything. The brand new non-approved euro cat I initially fitted to my Astra with similar symptoms to yours was within a couple of degrees at the exit compared to the inlet despite the cat itself being literally cherry red after a good thrash. The very definition of useless.

Rule all this out before you start taking things to pieces or buying new parts.

[mattrb]

Any update on this? I'd be interested to know how it worked out for you.

[datman]

me too. 98 Honda crv failed mot today 0.54 CO lambda reading on printout 1.003 (fine) i suspect the cat. 131,000 miles