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Author: Subject: Tin-top - Emissions Fail on CO (Duratec)

posted on 21/10/21 at 10:25 AM Reply With Quote
Tin-top - Emissions Fail on CO (Duratec)

Not entirely unexpected, but me old tin-top has failed its MOT
(2008 C-Max - 1.8 petrol duratec)

But annoyingly it failed on carbon monoxide and an exhaust leak (probably just after the CAT)

And just to put the cherry on top it’s a combined manifold+CAT+Flexi thing that isn’t exactly cheap… (£440+VAT from the usual motorfactors)
OE: 1671635:

And that’s assuming the Lamda sensors are fine (otherwise add another £75 each)

Financially its borderline whether the car is worth sorting even if it was definitely going to sort it…
its only done 102k, but its also got a fair bit of rust on both subframes & the rear suspension arms (just advisory on the MOT, but they are getting pretty rough) and it could do with new front shocks too…

also just to cap it off the garage reckon it’s a subframe off job (although I think it ‘might’ come out the top if I remove all the plastic crap under the windscreen (although I can’t find anyone else that’s done this yet….)

I’m 100% sure that its not worth sorting – but a replacement car that’s worth having is proving hard to find on my budget

So any suggestions on what else / how to try and figure out the actual cause of the high CO reading before I spend any cash ?
Also can anyone recommend me a good source for a cheaper CAT ? (I’ve googled and a few come up, but not from places I know)

Failing that does anyone know of a decent car for sale ? – looking for C-Max/S-Max/Mondeo Estate type thing (or similar – been looking at the fords mostly cause they are cheaper and I don’t much fancy the modern French stuff) but must be a petrol and preferably manual

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posted on 21/10/21 at 10:39 AM Reply With Quote
I would say better the devil you know until the market settles. Unless its a subframe off job

I have got one to limp through its test before now with a bottle of cat clean and a dam good thrashing.

But you will still need to fix the leak.

If it's a subframe off job the costs will add up as somthing won't come off with out rounding or snapping.

If it's the same as a mk3 mondeo then you meant to use alignment dowls to refit the subframe.

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posted on 21/10/21 at 10:49 AM Reply With Quote
Was it actually high CO?

An exhaust leak after the cat can let air in, and give readings outside the permitted range for lambda.

And another slight worry, what caused the CAT to fail? Usually there is an underlying cause so a new cat will last a year, especially the cheaper type. could be something like a temp sensor thinking enrichment is needed, and the cat can only do so much before it becomes inefficient.

On the plus side, what is the scrap value of the cat? It may surprise you. (mk2 MX5 are £750 I believe, but values vary wildly)

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posted on 21/10/21 at 11:10 AM Reply With Quote
Cut out the existing CAT & weld in a universal one, all done in situ? - tho' looks like that could be a bit awkward & messy from the shape of what you have, but, as already said something has to be causing the high CO in the first place, most likely culprit lambda sensor, I think I'd try to fix the problem first & try some CAT cleaner, see if it recovers, the leak could be temporarily bodged to perhaps give you another year?

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posted on 21/10/21 at 11:25 AM Reply With Quote
The exhaust leak could well be the source of high co, anywhere gas is leaking out air will be getting back in which will make the lambda sensor readings show lean, and the ecu will try and compensate for a lean mixture by addng more fuel. This will overload the catalyst and make it unable to oxidize the co to co2.

If you have a scan tool, look at the short/long term fuel trims, any more than 5% is likely to be caused by the above.

I also have had a few of the 1.8's that drink oil, that can also damage the lambda sensors over time and cause the readings to be offset from lambda=1


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posted on 21/10/21 at 11:45 AM Reply With Quote
just picked it up now - emissons print shows:

80°C temp

Fast Idle test:
2570 RPM
0.03 % vol CO
22 ppm HC
1.039 Lamda fail

Second fast Idle Test:
2540 RPM
0.73 % vol CO fail
175 ppm HC
1.020 Lamda

Natural Idle:
585 RPM fail
0.10 % vol CO

so a bit all over the place

My scan tool died a we while back so I'll need to beg / borrow one - but I did stick the dashboard test mode on - no codes, but it showed the engine temp at 124°C after a 10 min trip, but normal on the gauge - so the temp sensor is looking suspect...

also I've found you can get pre-made repair pipe sections for the flexi bit after the CAT for £45-50

what I don't have is a gas anayliser to see if any of this is worthwhile....

[Edited on 21/10/2021 by mcerd1]

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posted on 21/10/21 at 12:20 PM Reply With Quote
Are you sure its the cat? With those emissions figures it should have triggered the check engine light. The fault code would then point you to the probable cause. I would have thought lambda sensors. Does or has the exhaust been making a jingling sound recently?
Again as others have said the second hand car market has gone made recently with cars selling for £1000's over book so stick with what you have until things settle down.
Have just read your emissions figures, that could be due to the leak, you may be able to get just the leak repaired.
I also had the same issue with the coolant temp on a Mondeo 1.8 - the sensor had died, kept causing the rad fan to come on even when cold, that may be worth a check too as it might correct the low idle

[Edited on 21/10/21 by chillis]

[Edited on 21/10/21 by chillis]

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posted on 21/10/21 at 12:38 PM Reply With Quote
Originally posted by chillis
Are you sure its the cat?
No not at all sure

I'm now thinking - try and fix the leak - these repair pipes could be all that takes:

then look at the temp sensors - the fact that the ODB thinks its 124°C while the gauge shows 'normal' gives me something to look at (and the sensors are only £20 - 25)

then maybe just a bottle of cat cleaner (probably just a placebo but...) and then chance a re-test ?

the garage the did the MOT is on holiday now anyway so I've got at least a week to mess about with it before I can re-test it anyway....

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posted on 21/10/21 at 05:53 PM Reply With Quote
The temperature being reported is the cylinder head temperature, this is usually about 40°c hotter than the coolant, so sounds fairly normal.

Your mot emissions results indicate the catalyst was working fine during the first fast idle test but lambda was too high due to the leak, the second fast idle indicates the fuel trims had richened to a point where the catalyst stopped working, the idle test show the catalyst coping with the idle gas fine, i guess they didn't fail you on idle speed, as there is only provision in the manual to fail on it being too high - our machine at work does this on the printouts, and snap on have never fixed it.

Going by all that, the repair section should work, providing there are no further leaks once fitted. It is only a mild steel system, so could be welded if necessary.


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posted on 21/10/21 at 05:56 PM Reply With Quote
Gut feeling is the cats ok from those readings. Either air leak on the manifold or a lazy lambda.

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posted on 22/10/21 at 05:42 PM Reply With Quote
Those results look almost identical to my recent fail on my Jimny, garage advised the exhaust leak I knew about would be causing the problem (and the leak was quite far post lambda sensor) - welded a new joint in and sealed it up properly and it passed with flying colours. I expect as soon as you’ve sorted the leak that the issue will be gone.
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posted on 22/10/21 at 11:11 PM Reply With Quote
Normally if the the cat or the O2 sensors are bad or if there is an upstream exhaust leak expect to se a P0420 cat efficiency code
The fuel trims short and long term need read in live data.
You need to used a graphing OBD2 tool compare the upstream and downstream lambda sensor outptput .
Normally the upstream sensor (B1S1) will continuous "switch" between 0.1 and 0.9 volts with a frequency around once per second if the downstream sensor (B1S2) mirrors the upstream sensor the cat is cream crackered.

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posted on 25/10/21 at 04:17 PM Reply With Quote
managed to borrow a scan tool for a few hours

this is the lamda sensors when cold:

but as it warmed up it starts looking better (I think, I don't know really...)

one end of the offending flexi pipe:

and the next part of the job is to cut this just before the lamda sensor you can see here and move the sensor over to the new bit of pipe:

just waiting for the repair section to arrive now.....

[Edited on 25/10/2021 by mcerd1]

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posted on 25/10/21 at 06:03 PM Reply With Quote
The lambda sensors are working fine, the catalyst is receiving a slightly rich exhaust gas mixture but is operating ok, the fuel trims should all sort themselves out with a drive once the repair section has been fitted.


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Mr Whippy

posted on 29/10/21 at 11:48 AM Reply With Quote
Our old Cmax was a dreadful car I was so desperate to get rid of I practically gave away. Not even 40k on it and I'd replaced most of the suspension,, brakes, exhaust etc. Every mot was a nightmare. Just such a poorly engineered car it was a disgrace. I would never recommend trying to keep an old one going.
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posted on 29/10/21 at 01:38 PM Reply With Quote
^^ to be honest this one has been fine - I've had it for nearly 8 years now and I've personally put 55k miles on it...

the issues I've had are hardly unexpected on a 14 year old car with 102k on the clock and its not had an easy life (lots of short trips and hard driving) and I hardly has to do anything to it the first 5 years I had it....

if it makes a difference mine is the updated/facelifted 2007-2011 version - its got quite a few changes to the original including totally different wiring and much bigger ball joints in the suspension etc.
I've been told the 03-07 cars had more issues - its like the early one was just a testbed for the 05+ focus that shared the platform....

[Edited on 29/10/2021 by mcerd1]

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posted on 10/11/21 at 01:35 PM Reply With Quote

well I seam to have fixed the leak in the flexi.

I did splash out on a proper O2 sensor socket, so it made it pretty easy to get the old sensor out and back in without damaging it
(really wasn't sure I could get it out after 14 years...)

Total PITA of a job to do on the car - working in a tunnel at arms reach with barely enough room for my fairly skinny arms, but there was no way I was pulling the subframe off and the whole manifold+CAT thing off the head

but after several hours of swearing at it I've got a result of 0.05% vol CO at 2720 RPM and 1.003 Lamda
and 0.30% on the idle at 1045 rpm (so not great, but a pass)
So it looks like the exhaust leak was the main issue just as you guys though

So now its got a fresh MOT the first thing is to change the offside driveshaft as the inner joint seems to be eating itself

[Edited on 10/11/2021 by mcerd1]

[Edited on 10/11/2021 by mcerd1]

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