CO too high

Hi all, took my 1991 cabriolet 1.8 GTi for MOT and failed it due to very high emmisions, was speaking to the tester and told me when he started the test the CO were at 10.4 and he has adjusted it to 6.3 but that's all it's dropping to and not anymore. What could I do to drop them further more down to get it correct. He did say that check timing is correct, new air filter, plugs and cleaning the metering head and see if that makes a difference. I am starting with the timing first cause the plugs and air filter has been changed 2 months ago. Any help with this would be much appreciated and thanks again.

Carbed or Injected?

See Cabby-info.com Tech, Ignition, DIY timing, Method 2 for Digifants.  All you need is a DVOM.

GTI also what is a DVOM sorry for being stupid

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Greenmk1 said

GTI also what is a DVOM sorry for being stupid

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Digital volt ohm metre?

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Did the chap indicate what he adjusted to lower the CO level?

Should be the small hole on the metering head and used a Allen key, then I guess the idle speed would also need adjustment

Hi I ve not manage to sort it yet due to family commitments but once I get it or do anything to it will put it on here. Thanks so far

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Hi all, sorry for very late reply back, ok so I got the CO as close to 1.4 at MOT centre but when I got home and tested on my Gunson after about a month it was showing 0.4 and once fan kicked in it increased to 1.2. I know at idle it should be 1.6 but when the fan kicks in would it increase and once it stops it drops back down. Please see images attached.

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I would leave the mixture alone and ignore the Gunson tester as they are not very accurate.
The MOT testing equipment is the one to to with.and the CO is about right.
After a long run, left the car cool down and then look at the colour of the spark plugs as that will give you a good idea of how it's burning fuel.

White - To lean
Grey - Spot on
Black - To rich.

Thanks I ll look into the plugs after a good run

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Not sure I'd agree that Gunsons aren't accurate…

Looks like you've forked out for a new one and they aren't cheap.

Also sounds like you're keen to learn how to keep your car running properly and all credit to you for doing it… so stick with it, likely be frustrating at times, but it's very doable in the end.

I've the same Gunson as yours, although it's not that snazzy green, just plain old black -  tester envy!

Yes the reading will increase if the fan kicks in, bit of a pain, but you need to let it finish its cycle and for things to settle back down again before continuing with the test.

Be the first to admit they're a bit fiddly and if you don't stick to the letter of the setting up / use instructions you're really just wasting your time.

Practise is the key, and a light touch… when you get the hang of it you'll probably be surprised how little the adjustments need to be to get noticble changes.

You'll also get an 'ear' for your particular engine, should eventually be nearly able to set it without having to look at the readings.

I've had mine a few years now and put a couple of cars through their MOT's after setting the CO with the Gunson.

One was a Peugeot 205 on L-Jetronic and the other a MK2 Golf with Digifant, maybe not exactly what you have, but variations on a theme.

These are the 205's / MOT centers readings (theirs is to 3 decimal points against the Gunsons 1).

2021 - 1.3% on the Gunson / the test center 1.320

2022 - 1.5% on the Gunson / the test center 1.530

It's going back in again in a few weeks and I did the CO a short time ago, it hadn't drifted more than a few fractions after a year / hundreds of miles.

https://www.manualslib.com/manual/1482901/Gunson-Gastester-G4125.html?page=5#manual










 

Hi all, I checked the plugs and they were black (running rich as stated) and now when I turn the mixture down to make it lean it struggles to start. What is it that I am doing here that it is struggling to start and even idle.

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Well that's a pain in the bottom…

Not sure what's going on but what I would try next is get the mixture back to where it was before, clean the spark plugs with a wire brush so they are nice and clean and if the type you can gap, check the gap is right.

Give it another good run and see what colour they are.

Is the exhaust note and constant sound or "hunting"?

Hi all, ok so after a lot of messing about with the CO levels I have took it for a long drive and seems a bit sluggish at first start up and slow at picking up until a couple of miles then once I switch ignition off wait about 15 secs and start it, it runs a lot better. So went for a long drive got home and checked the colour of the plugs and they seem a bit on the white side. Please see image and let me know what you guys think. Also the temperature guage is about 3/4 before it was around 1/2. Any info is much appreciated thanks in advance.

Please see images

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