MOT Fail Emissions Advice

[Elsaetka]

Hi

Some advice would be greatly appreciated as i'm a little 'stuck' as to the best steps to take.....

My 1990 DG 1.9 (Waterboxer) was MOT'd yesterday at a local garage, (more of a tyre, exhausts, brakes, servicing and light repairs provider if you catch my drift, but their quality and service has always been brilliant, I have no problem with the quality whatsoever).

They called me to say it has failed for a snapped rear spring (which is easily sorted with two new rear's), however, the other fail is 'exhaust emissions, carbon monoxide content excessive'.

They explained that the MOT testing technician said the mixture screw will probably need adjusting, however did not want to touch it as in all honesty he 'did'nt have a clue' about that type of vehicle. (fair enough I suppose). I have 10 working days to sort it and get it back.

However, this leaves me with a problem. Two years ago I was told by a VW dealership they had to put Fortron in the fuel to get the emissions low enough to pass, so last year immediately before test I changed the plugs, oil (and filter), and air filter. Plus stuck Wynn's emissions reducer in the tank, so it passed.

I was complacent this year, in the sense that I did not change anything or add emissions reducer, however in fairness, the camper has done very few miles since last MOT. I did give it a good run to fully warm it up before taking it in.

No doubt many other 1.9 DG owners have or will experience this problem so my questions to those with experience are:

1. Is sticking emissions reducer in the tank and changing the oil and filter likely to do the trick? Perhaps changing the plugs and air filter too,however they have not covered many miles?
2. What are the MOT emission tolerances for this model T25? Not the actual vehicle optimum, I mean the DVLA MOT tolerances. I didnt get a print out.
3. I have considered the carb mixture settings (Standrard Pierberg 2E3). It does smell of un-burned fuel when warmed up to me, always has, however I am balancing that against the age and emissions of my vehicle compared to modern cas which practically omit nothing. The idle speed is fractionally fast, I need to drop it about 50 / 100 RPM.
The carb has a new choke operating system and is 100% open when warmed up, so no problems there. I'm slightly loathed to tinker, but if anyone can give a definative guide to setting the mixture it would be appreciated. I understand the screw is behind a tamper proof cap, clockwise leans it I believe.
I do have an emissions tester, I don't know how accurate it will be.

Thanks in advance for replies.

[kevtherev]

Reducing emissions is not done with additions to fuel.
I would fix the problem not mask it.
So that's out.
What was the 2000 rpm CO reading?
What were the HC readings like?

High CO can be caused by a few things
Air leaks into the induction side causing slight misfire
Poor or weak spark.
Mixture ratio at idle incorrect
Air filter blocked

Tickover speed is 900 rpm
If the CO reading is a pass at 2000 rpm then the examiner must pass the vehicle in the test

[ajsimmo]

The limits are 3.5% CO, and 1200ppm HC. If it's over those there's something wrong, as the limits are very generous. Optimum CO at idle (petrol) is around 1.5%. HC on a healthy engine is often around 300 so there's lots of headroom!
I suggest screwing in the mixture screw until idle drops slightly, then out between 1/4 and 1/2 turn. Measure CO. If it's below 3.5%, but HC is high, you probably have an airleak causing a misfire or oil contamination with petrol. In this instance, revs should be raised to 2000rpm by the tester at MOT, if HC then falls below 1200 for 5 seconds, it passes the HC test.

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[Elsaetka]

Thank you.

I was not given a printout of the emissions, I don't know if an MOT test station is legally required to provide the information but it would have been very handy. The only description on the failure sheet is as below: 'exhaust emissions, carbon monoxide content excessive'. The garage is okay, but i'm probably wasting my time and breath going back to them regarding the test technicalities, raising revs etc. although I appreciate you are correct.

Many thanks for the MOT emissions figures, that's why I asked the question, as I suspected there is a lot of headroom, so your replies confirm i'm looking at a fault. (Mind you, although I will fix it pronto, my main concern right at this minute is a new MOT as without i'm very restricted).

So, now thanks to these initial replies i'm looking at a 'proper' fix. As I say, I have a emissions tester however as to how accurate it is I don't know. Nothing wrong with giving it a try of course, if I had access to an actual calibrated MOT analyser I would be laughing.

Unless I hear different I think I will go for your suggestion Ajsimmo and alter the mixture screw as described, while still running my emissions tester too, I might as well try it.

If all else fails after forum assistance, I have a former VW CV master Tech friend with his own garage could go to him if I can't fix it.

[Ian Hulley]

Get it nice and warm and get your base line BEFORE you start turning anything. See what the CO is on your tester.

Ian

[shepster]

Two years ago I was told by a VW dealership they had to put Fortron in the fuel to get the emissions low enough to pass, so last year immediately before test I changed the plugs, oil (and filter), and air filter. Plus stuck Wynn's emissions reducer in the tank, so it passed.

Why not do that again?

[Elsaetka]

Here's a further update.
Firstly, I have just noticed the failure sheet has the emissions result print attached to the back, I had'nt noticed, it reads as follows....

Description:
CO 3.56 %Vol
HC 350 ppm
----------------
Summary Results:
Idle speed pass
Smoke level pass
CO (3.50) fail
HC (1200) pass

Exhaust Emissions Test
Overall Result: Failed.

I appreciate sticking an additive in the fuel could sort it short term, i.e. get it through test, however as Kev wrote initially, that's just masking the problem and I try to keep it as tip top as possible. I know these vehicles are not good on MPG at the best of times, but mine is really bad so needs to be sorted. Fortunately I keep the oil and filter changed regularly, however I will feel far more comfortable with a 'proper' fix.
Thanks to the posts, and some further thoughts, I decided to discuss the situation with a friend of mine who is a qualified VW Master Tech, (cars and commercials who has his own place).
He is going to sort the emissions using a calibrated emissions tester (when it's fully up to temperature), then take it for test himself. I'm going to change the oil, filters and plugs before taking it in (In two days time).
I will report back as it's important to help others who will find themselves in this situation.
Watch this space in due course.

[ajsimmo]

That result is so close to a pass it doesn't indicate any underlying fault, other than idle mixture screw needs turning in a fraction. HC result is very good so I don't think you have anything to worry about, just needs a tweak on the analyser before test.

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[kevtherev]

Agreed
I would change the cap and rotor arm
Those figures shout slight misfire due to weak spark.

for me anyway

[ajsimmo]

I disagree, HC would be raised by a misfire (by unburnt fuel). He's burning pretty cleanly at 350, but CO is slightly raised, so it's a bit rich on all cylinders (no air leak then). All that's needed here is 2 minutes on a gas analyser and a small flat screwdriver.
It's times like this where LPG would show up the real problem (or absence of one).

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[kevtherev]

OK
Remind me is the mixture screw air bleed or fuel bleed



No harm in changing the cap and arm if not done so recently.

[itchyfeet]

looks like air and fuel to me

[kevtherev]

Fair enoughsky.
I thought it was just fuel.

[Elsaetka]

Great replies, many thanks. I can't give a further update as it goes in tomorrow.

I can say for definite that the plugs (Bosch WR7DC+ (+1)'s have only covered about 2,000 miles max, as had the air filter and oil. Once up to temperature it pulls like a train, (Well, a good T25 at leaDistributor cap and leads are also new. I would go with mixture adjustment, but hey ho, time will soon tell. I changed the oil and filter today, plus the air filter, although it was very clean indeed, it would be after so little mileage.

[Elsaetka]

Great replies, many thanks. I can't give a further update as it goes in tomorrow.

I can say for definite that the plugs (Bosch WR7DC+ (+1)'s have only covered about 2,000 miles max, as had the air filter and oil. Once up to temperature it pulls like a train, (Well, a good T25 ).

Distributor cap and leads are also only a year old, so I would go with mixture adjustment, but hey ho, time will soon tell. I changed the oil and filter today, plus the air filter, although it was very clean indeed, it would be after so little mileage.