MOT - Carbon Monoxide level

[John Marshall]

Hi Everyone,

A question for you.

Jazz CVT 63 plate - 25K miles Carbon monoxide level from MOT

Last years carbon monoxide level was 0.01 %vol - the limit is 0.30
This years carbon monoxide level was 0.26 % vol - again the limit is 0.30

This is a large increase over last years test.

The only difference I can think of is last year I drove for approx. 1 hour to make sure the car was fully warmed up before I had the car tested, this was done straight away while I waited.

This year I only drove for 15 min to warm the engine and there was a 15 min wait before the test

My question is - what is the chance of the carbon monoxide level being out of spec. on next years test and is there anything that I can do about it

Thanks in anticipation

John

[Johncb500]

You could be correct.

Before the MOT I normally take the car for a  decent thrash.

Get the Cat hot to burn any rubbish off it.also clean the discs and pads.

I have been told the handbrake on a Jazz is a weakness

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[sparky Paul]

Presume that's the natural idle, do you know what the fast idle result was?

What was the HC result?

If the HC is up too, the cat was probably not up to operating temperature when tested. If the HC is low, then you may have an exhaust leak at the manifold joint.

I don't think I would worry too much about it, just take it for a run before next year's test and see how it goes.

[Jocko]

I always give my car a thrash going in for its MOT. It is only a 12-mile run, but I keep the revs up around 4,500 for the duration, up and down the box and serious braking for corners (It is a fast B-Road that used to be a main A road).
It is great fun and therapeutic for me as well as the car.
This year I also tipped a bottle of "Redex Emission Reducer" in, the fill up before the test.

[sparky Paul]

I always give my car a thrash going in for its MOT. It is only a 12-mile run, but I keep the revs up around 4,500 for the duration, up and down the box and serious braking for corners (It is a fast B-Road that used to be a main A road).
It is great fun and therapeutic for me as well as the car.

I do the same. I'm only a couple of miles away from my MOT man, so I go on a bit of a tour before driving in and testing it. I always book for first thing, so we can stick it straight on the analyser.

When the car goes for its 'Italian tune-up', I always think it would be an interesting stop for the Police, expecting to find an 18 year old yobbo with a baseball cap driving ... 

[Jocko]

I always think it would be an interesting stop for the Police, expecting to find an 18 year old yobbo with a baseball cap driving

My thoughts exactly.

[Johncb500]

I always think it would be an interesting stop for the Police, expecting to find an 18 year old yobbo with a baseball cap driving

My thoughts exactly.

Great minds think alike.


Another thought. Maybe if you use supermarkets fuel.

Get a thankful of branded fuel a couple of weeks before the test.

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[Johncb500]

Read tank full !!!!

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[Jocko]

Read tank full !!!!

My brother and I play golf over the internet and we type chat messages as we play. Or at least I type and he uses voice recognition software on the iPad. His messages read a bit like the policeman on "Allo, Allo" crossed with someone suffering from Tourettes.

[John Marshall]

Thanks everyone

Presume that's the natural idle, do you know what the fast idle result was?

What was the HC result?

Yes the results were for "natural idle test"

Fast idle was yr 2020 = 0.00 ... yr 2021 = 0.00   against a limit of 0.20 % vol max

The "HC" result yr 2020 = 1 ppm    yr 2021 = 2 ppm against a limit of 200 ppm max

John

[sparky Paul]

Good fast idle CO result shows you that the cat is healthy, and no hydrocarbons is good news for the engine.

Maybe you have a bit of a leak at the manifold joint which is sucking air in at idle, maybe not. Maybe the tester was yapping and didn't let the revs drop soon enough for the natural idle test, not allowing the CO to drop properly in the allotted time. Who knows. I've had the odd anomalous emissions result which have returned back to the norm the year after.

Either way, I wouldn't worry too much so long as it's running okay, Just make sure servicing is kept up to scratch, give it a good run before the next MOT, and make sure it's hot when it goes in.

[Jocko]

Maybe the tester was yapping and didn't let the revs drop soon enough for the natural idle test, not allowing the CO to drop properly in the allotted time.

If they do the test, and it is in spec, they will let it go. If it failed the first time they repeat it and if it now passes that is the one which is logged.

[sparky Paul]

If they do the test, and it is in spec, they will let it go. If it failed the first time they repeat it and if it now passes that is the one which is logged.

That's true, as soon as they get a result within the limits, that's it - test over. To repeat it after a failed test, they have to repeat the whole emissions test from the beginning, which doesn't take long. It's a bit different with diesel emissions, where you get five goes at passing the opacity test.

[embee]

My guess would be that the engine/cat wasn't hot enough. It needs to be near 300C typically for conversion to start, and if the engine isn't hot it could be running on open loop especially if they didn't wait long enough for it go closed loop after starting. If it's running OK and there are no check-engine lights showing I wouldn't worry, put it down as a test anomaly rather than an engine fault.
The other possible cause is a fault with the analyser, but since the other measurements were so low I would probably rule that out. Analysers are somewhat sensitive devices and I can well imagine in an MOT garage they don't always get treated properly (coming from the motor industry using £250k+ Horiba analysers).
I have a 1995 Suzuki Cappuccino which is always borderline on MOT emissions (It's an official UK car but it was effectively a Japanese emission spec), and it is essential to get it properly hot otherwise the cat temp drops off and conversion more or less stops. Fortunately the testing station I use knows me and the car well and always make it pass 

[sparky Paul]

My guess would be that the engine/cat wasn't hot enough.

No problem with fast idle test CO, which suggests cat functioning normally?