Failed MOT on Emissions (CO only)

25th June 2009, 22:25

Hello,

I took my Saxo 1.4 VSX (1997) in for an MOT and it failed on emissions both
times. The first MOT passed the CO test at natural idle but failed the fast
idle tests. The second time I put some redex in a full tank and drove about
200 miles ragging it quite a bit (this got the tank down to about halfway)

Before I took it in I then filled it right up again, so still some redex in the
system. I drove it hard for several miles right before the test as I did before
also and also took the air filter out. Unfortunately it failed again only worse
this time.

Below are the results of both MOT tests

==============================================
FIRST MOT TEST

Fast idle Test

CO = 0.61% (Limit 0.3) FAIL
HC = 25 ppm (limit 200) PASS
Lambda = 1.002 Limit (1.03) PASS

2nd Fast Idle

CO = 0.56% (Limit 0.3) FAIL
HC = 18 ppm (limit 200) PASS
Lambda = 0.997 Limit (1.03) minimum limit is 0.97 PASS

Natural Idle Test

CO = 0.47 (limit 0.5%) PASS

======================================

=======================================
2nd MOT results

Fast idle Test

CO = 0.68% (Limit 0.3) FAIL
HC = 39 ppm (limit 200) PASS
Lambda = 1.002 Limit (1.03) PASS

2nd Fast Idle

CO = 0.45% (Limit 0.3) FAIL
HC = 71 ppm (limit 200) PASS
Lambda = 1.011 Limit (1.03) minimum limit is 0.97 PASS

Natural Idle Test

CO = 0.68 (limit 0.5%) FAIL

===========================================

Now can anyone tell me what the likely cause of the failure is?
Did the redex do it in? did not having an air filter actually make it worse?
did ragging the car at high revs do it in?

Before the first test I changed my lambda sensor for a new bosch one.
The old one had silicon on it back from the dodgy tesco fuel. Also I had
a new (although cheap) catalytic converter fitted about 8 months ago.
Could the lambda sensor being crap have damaged the CAT?
I changed the spark plugs around the same time too.

The fuel efficiency is good at about 45 MPG.

Other problems with the car,

I feel that it lacks power compared to what I expected, it feels like it has
less power than my old 1.2 clio.

When pulling away and accelerating in first and second it sometimes
doesnt go and pauses a bit a few times. The revs dont jump up so
I dont think its the clutch slipping... Also very rarely the rev counter
isnt very smooth when letting off the power and jumps down say to 2500
to 1500 then to 1000.

If anyone can give me some idea of whats wrong I would appreciate it
as I am not sure what to do about it.

Cheers

25th June 2009, 22:34

Hi,

If your oxygen sensor was contaminated with silicon then your catalytic converter will be too if they were both on the car at the same time as when the contamination occured.

I assume that the sensor was coated with a white substance.

Cheers

25th June 2009, 22:37

catback?

25th June 2009, 22:41

Check your plugs first and see what colour they are.
We've had loads of Saxo's fail on Co and its been something simple like the plugs being black.

If they are black and "sooty" give them a wire brush and put them back in.
Other than that we have had similar problems with cheap replacement cats which arent as effective as the original equipment items.

Chris

25th June 2009, 22:43

Thanks for the reply.

I bought the car in about August of last year.

I think the contamination of Tesco petrol was in 2007 wasnt it? I know the person
who had the car only ever filled up at tesco so its probably been like that since back then.

When I took the lambda sensor out it had a fine white power on it, just like images I have found online.

So the CAT was replaced long after the old lambda sensor was messed up, but I wonder
if by having a duff sensor the CAT is likely to have been damaged.

25th June 2009, 22:48

I will re-check the sparks, I have a feeling when I took them out last time oil may
have got into one of them perhaps that's happened again.

What else could be causing it to fail only on CO?

Also what else could cause the flat spots i get when accelerating.

(The car has done about 75k)

25th June 2009, 23:40

Crap cat, its not efficient enough to pass MOT, also it is probably restrictive enough to rob you of some power as well. Try get a decent cat from scrappy etc mate or find a friendlier mot station.

16th August 2009, 13:47

Stevo I think you right including it robbing me of power. Even after below it still feels
like something is wrong with it.

Anyway here is what happened.

When I went to the place which fitted the CAT in the first place they tested
it and it failed again. It was suggested that an air leak could be a problem
so I went a way and indeed they was one. I had a leak in the pipe which
lets oil vapours into the air filter and some other separate part.

I took it back for a test and it came out no better, although I had more
power so it did do something. Interestingly the HC went up from a very
low 22 to 55.

Anyway they said they could take it in and look at the engine codes,
sensors etc and fix it. A few hours later they phone to tell me they have
got it sorted.

So when I get down there they tell me they changed the CAT and though
it did get a bit better it wasn't enough to pass, so they checked the ECU
and found that a temperature sensor was faulty and when they changed
that it fixed it.

Now personally I don't think how the story goes even makes sense, why
would you change the CAT first when they were telling me that if they
change the CAT and it doesn't work they will have to charge me.
Surely you would perform the ECU check first as it costs them nothing.
(I do not even believe they changed the sensor of even did the test)

I now feel like I have been ripped off £80 but still it could have been
worse.

If the same situation happened again and my CO was around 0.6 and
my HC was very good at 20-60 then I would have just had them change
the CAT. Its just basic chemistry if you have a good burn with plenty of
Oxygen you will therefore get low HC. Therefore there is nothing major
wrong with the car.

16th August 2009, 13:58

mate it goes to say if it was you doing the work you do the cheepist thing first but in a garadge thay just fire in what thay think it is and thats what you have to pay if it wasent the cat i would demand thay put your old one on as thay have admitted that it wasent at fault try mate whats the worst that could happen

16th August 2011, 19:34

So here I am a few years on and failed the MOT again with CO slightly higher than the limit.

It only got passed the last few years I reckon as the people at the garage remembered me and now as the CAT is just out of warranty they failed it.

So anyway I am after a new CAT and all i see are cheapo ceramic monolith ones which I guess mine is. All the ones I can find are BM90021 and if it doesn have that it doesnt say anything. No doubt thats probably what i have now.

looks like I either buy a new cat every year for £40 or just swap it over every year for the MOT.

Where can I get a steel monolith one? or does anyone know a part number for one.

18th August 2011, 07:45

My mates failed really badly on emissions last week, (CO was 1.5%!!) changed cat and spark plugs and got it through with CO at 0.27

We bought cat for £46 from euro car parts, on checking again it is a ceramic one but changing this alone brought CO down from 1.5% to 0.8%, plugs did the rest.

I'd check plugs again before changing cat as they're much cheaper and easier to replace.

28th March 2012, 21:16

As an update I failed the MOT with another brand new cheap CAT which was from eurocar parts. The emissions were exactly the same as before so in the end I went and bought a proper one from citroen and it passed easy.

29th March 2012, 20:55

get a new cat pal