Author Topic: MOT CO levels  (Read 818 times)

Offline physicsfool

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MOT CO levels
« on: December 21, 2016, 12:15:32 pm »
Having a slight problem with the emission control part of my MOT.

No other advisories except that the CO level is massively over what it should be. According to my chum it should be 3.5 or less and mine is blowing an 8. he said that was taken when the car was warm, I dont have a cat in anymore.

Any advice? The engine is a 1341 block with 65mm pulley on a PSD full blend. MAP is a PPP G40 005 jobbie with the spec to match that

Cheers and Merry Christmas Y'all

Offline Yoof

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Re: MOT CO levels
« Reply #1 on: December 21, 2016, 01:42:41 pm »
That's a non-CAT limit (CO < 3.5% and HC < 1200ppm)

Assuming all engine sensors are healthy - check the CO Pot (preferably when it's hooked up to his kit.

Online polo classic

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Re: MOT CO levels
« Reply #2 on: December 21, 2016, 02:47:12 pm »
in my experience, when CO is that much over, it is normally the lambda sensor that needs replacing

Offline physicsfool

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Re: MOT CO levels
« Reply #3 on: December 21, 2016, 03:16:27 pm »
Cheers Pete,  after reading the diagnostic guide and consulting Dr Mirfin I am lead to believe I have a sensor out. As the revs are dropping asI unplug the blue temp at running temp. Ordered up a new blue temp and lambda. Will check earth's and wiring

Offline Rich_Royal

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Re: MOT CO levels
« Reply #4 on: December 25, 2016, 09:46:49 am »
Hi Martin, merry christmas  ;)

I had a similar issue last month with my MOT, no physical issues with the car what so ever but it failed emissions, mine was around 6% when it needed to be 3.5%,

The guy doing the test let me mess with it and offered to test it straight away so I reset the idle and just wound in the carbon potentiometer, it then sat steady at 3.2% but when he ran the 15 second test it was about 3.6-3.8 then just dipped below in the last 3 seconds which was enough for a pass,

I came home and did some reading and found this thread on here which is very helpful:

https://www.polog40.co.uk/forum/index.php?topic=214.0

I plan on messing with mine next spring and setting it up properly, I've got a new temp sensor as well and I'm gonna go round and check everything else but most of my engine is new anyway as it has been re-built so I suspect it might be down to the PPP chip i'm using - I'm tempted to try and track down a place that will do a proper rolling road tune but we'll see.

As for the blue temp sensor, on MOT day if I un-plugged it the revs dropped, which according to that thread means I might have faulty sensor somewhere? or does that mean the blue temp sensor is faulty? I had the car out of the garage the other day and it wasn't up to temp but I unplugged the blue temp sensor again and the revs stayed the same? I've got a new one anyway so I'll swap it out but doesn't make sense for that to be a cause of such high emissions.

Good luck with it, if you find any obvious cause can you post it up.
« Last Edit: December 25, 2016, 09:54:40 am by Rich_Royal »

Offline physicsfool

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Re: MOT CO levels
« Reply #5 on: January 05, 2017, 02:41:08 pm »
Cheers for that Rich,

Managed to get back to the car this morning and change blue temp, co pot and lambda. Only the blue temp was new, meaning to refresh it anyway (22 from VW, apparently the skoda fabia uses the same sensor).

Turns out it was a faulty lambda, also being able to use my mates lift meant more skin left on my knuckles


The culprit, also the part number doesn't look quite right.


Good news, it passed its MOT and now time for a few days trips, dare I say a G40 summer meet

Offline vwmk3jon

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Re: MOT CO levels
« Reply #6 on: January 12, 2017, 04:20:32 am »
last time i got mine mot'd it went off the scale....so i cheated. i got my spare Co pot and turned it all the way down. swapped it right outside the garage and it sailed through the emission test and then i swapped it back before i drove home. not the ideal thing to do but it worked.