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MOT failure on emissions


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Today was my first MOT. After sorting other little issues before the test it sailed through - apart from on emissions. I think he said it should read 0.3 and it was on 8! It’s the same map as for the IVA (GBS EMISSIONS) and the only change is fitting a Lambda - which I thought helped things? 

anyone any idea apart from remove the lambda - although it’s been 3 years since I used the software so could do with a reminder on what to do 😬

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Was it the idle CO or the fast engine speed (~2500rpm normally) CO level that it failed on?

Does the car have a catalytic converter fitted, I am assuming yes because you'll have fun making those numbers without one :D. I wonder if the cat is damaged/no longer effective, that's all.

Burning any oil?

Is the exhaust nice and air-tight, no leaks?

What engine management is the car using? When the lambda was added, was the ECU reconfigured to make use of it correctly?

Assuming everything has been done right and is working correctly, then someone can tweak the fueling/advance for the load sites you're testing (either idle or fast engine test - you're not clear on which one it failed) to get that number down. You'll need someone with a gas analyser, or do it at the garage doing the test while it's on their analyser.

Edited by brumster
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Not sure the cat is relevant here ?   Like you I assume it is the CO we are talking about which needs to be below 0.3  As I understand it the CO level is to do with the mixture which should be controlled by the lambda sensor.   The purpose of the cat is to clean up the hydrocarbons and they were not mentioned.   I agree we need a lot more detail.

As an aside, having struggled with emissions during the early years, I blocked one of my exhaust outlets (a Superspec-specific design, not relevant to a normal 2B) then every year I add an injector cleaner to the fuel tank one fill up before the MOT and do a 40 min run just before the MOT, doing it all in 3rd gear so the revs sit around 4000+ rpm.  It's worked for the last 3 years, with straightforward passes 😀

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Agreed. But certainly at the idle test, the lambda is rarely in closed loop mode as I was always lead to believe that the mixture and combustion at idle is too irregular to get reliable readings off a wide-band lambda quick enough to adjust. Obviously if we're talking the 2500-3000rpm test here, that's different. Either way, depending on the management system, there is typically a configuration setting that will only allow the adaptive fueling to correct by a maximum amount of 5% (for example) so if they fueling is way off, it won't adjust enough to get where you need it to be. You can up the maximum allowed adjustment or just do a number of sessions of merging in the corrections to the base map and then going out and letting it learn again.

Personally, when I had issues with the MOT emissions test, I just sat and manually tweaked the fueling while watching the gas analyser on 'free measurement' mode. I'd offer to help but unfortunately my gas analyser has a failed cell in it which is £1k to fix, so I'm like, *bleep* that :D something to stick on eBay when i can get round to it!!

EDIT: Does a mod want to move this into a more appropriate section :D I get the mistake the OP made thinking "test" meant MOT related!

Edited by brumster
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Wow, some great questions there - way beyond my knowledge but I’ll see what I can do in terms of answers.

lambda - was a wideband as I was under the understanding this is what would help with economy and fuelling?

it was the idle speed that was over. But didn’t pass at any point, it was the idle that was most out. 

Cat. Not sure I have one? It’s the standard GBS Ford build and the MOT centre said I don’t have one this weekend - I thought I did as part of their exhaust? 

not burning oil as far as I’m aware. Still seems full 5000 miles in.

I don’t think I’ve got any exhaust leaks but will check at the weekend. 

As for adding the lambda correctly, I assume not. I think this may be where I’ve messed up as it’s on the same map it passed it’s IVA with. 

thank you for the help and advice this far, I really appreciate it.

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Sounds like the mapping just needs setting up, tweaking for the idle, possibly the throttle bodies need some tweaking/balancing... assuming everything is in good condition, gaskets are sealing, plugs are good, fuel pressure, injectors, etc.

Certainly just "plugging a lambda in" and expecting it to fix emissions is not how it works, I'm sorry to say :D;) not on aftermarket engine management anyway, assuming you're on Emerald for example (which I think is what GBS supplies?)

edit: I believe some of the GBS exhausts do include a cat at the front of the silencer?

Edited by brumster
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The early GBS exhaust had the CAT in front of the silencer, looked like a snake that had swallowed a rabbit.

Latter exhaust had the CAT in the front of the tube, bracket also changed around the same time from bobbin to the hook type, but there are a number of versions

The GBS IVA map is a base, starting point, it is close, but only if the throttle and start of the map are matched, a simple procedure, but I found rarely done.

Matched correctly the IVA map I used would generally fall in at idle, and will get very close at the fast run, however IVA emission is tested between 2500 and 3000 rpm.

The map starts to go lean at 2500 rpm, getting leaner toward 3000 rpm, you can change the mixture by careful adjustment of the throttle position whilst the test is carried out, but at 3000 it goes full rich again.

MOT just says rev above 2500 rpm, and I always had troubles with MOT, unless allowed to control the throttle. It's a fiddle as there is a delay between throttle and reaction on the tester.

Wide band lambda is the best way, but again in the map I know, will need switching on, and calibrating in software, the map then needs the target set.

It will have no effect on tick over, as someone said above, none will work there, again it's a case of matching map to throttles, which should make it fall in, after that, manually tweaking as required.

Fast idle will be controlled by Lambda. But it will only be good for the test, as from memory, and it is failing due to age, auxiliary fuelling is not mapped in the IVA map.

My info may be a little out of date now, but the IVA maps I know, and still have somewhere, were built for the three throttle bodies/induction systems that GBS were doing at the time, Jenvey, AT and Plenum. I do not know if maps were done for other options.

Best maps are those built specific for a vehicles setup, on a good rolling road, by someone who knows the ECU, and with Emerald I would get one for Emissions and one for Power, and have a map switch.

IVA and power maps I know are dated 26th July 2011, you can check with the software, but I am sure there are other versions out there, so approach above with care, but always match map to throttle unless it's built for your car.

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Wow, what a detailed reply. Thank you.


I had my retest yesterday and although I got caught in the rememants of this weekends storm - it failed again. The return fuel pipe issue is fixed but was still hitting 7.8 CO2 at idle. It’s meant to be 0.2 -0.3 apparently. Anyone know if it’s being tested against the right values?

it’s on an age related plate, 2.0l zetec engine, emerald ECU, standard GBS Plenum and exhaust. 

what’s the best was to mop out the foot wells which are under a good few mm of water…..😬

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CO2 should be a lot higher as the engine is burning hydrocarbon fuel ( petrol ) to CO2 and water.

I think that you mean CO ( carbon monoxide ) which for carbed cars is either 3.5% or 4.5% depending on age. So even a fail here.

Any Zero will probably new enough to not take advantage of visual smoke test only exemption for amature build vehicals.

Is the temperature sender reading correctly as if the ECU thinks that the engine is cold it could be deliberatly over fueling.

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Test paramours are set by the vehicle registration details.

Age related is the age of the engine at IVA, if not known, it would be set at the standards of the time.

Zetec engine for IVA will be


CO < 0.30
HC < 200

2500 – 3000 RPM

CO < 0.20
HC < 200
Lambda 0.997 – 1.030

For MOT it will be the same settings, but the test procedure, in the MOT emission tester software starts the test countdown at anything above 2500, it does not have the upper rpm, see previous for problem with that.

IanS is correct ECU temp should be reading similar to water temp or it will over fuel.

As mentioned before, my stuff may be out of date, but the original Zetec plenum map switched off fuel enrichment at 70 deg C, But there is air temp enrichment, so you will need to check that as well anything above 20 deg C is OK.

I assume you are using the Ford throttle body? which is often the culprit for it being that far out using the map details attached, the throttle butterfly is not flat so air flow through it is not progressive, and not helped by having to fit a throttle idle screw.

Have you matched the map to the throttle ?







map details.png

Edited by knights_templar
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  • 2 weeks later...

Sooooo, after a long drive up to GBS today they had a look at my emissions problem and diagnosed it within minutes. I’d set the lambda up wrong, not given it any power and somehow the fuelling was a complete mess. Matt wrote a new map for me and within 30 mins it was running sweet and hit the MOT parameters with ease. It’s now booked back in on Monday for a test and finally it should be back on the road. 

while there, Richard popped out to say hello and have a look at the car and quickly asked how it handled. I could tell something wasn’t right so asked why and he pointed out I’d fitted the steering arms upside down! 😳 he nearly fainted Hearn I said it’s been like that for 5000 miles and 3 years! 

they changed it as it was dangerous and then sorted the tracking - quite rightly at cost. The drive home was unbelievable, it’s like a new car. After they explained why it was so dangerous I can’t  believe I’ve not come off the road yet - neither could GBS!! Seems I’ve been lucky.

from Monday I should be back on the road, although probably missed the summer now 😬

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