96 2.0 GTI Emissions MOT Fail - adam f

Car failed its MOT on emissions today. The tester said there is 3 reasons why this could fail - Cat, Lamba sensor and anothere sensor (cant remeber what he said)

First fast idle

CO level = 0.61 %vol (0.30 maximum allowed)

second fast idle test

CO level = 0.50 %vol (0.30 max allowed)

Can anyone help with what i need to replace - from the above results?
96 2.0 GTI Emissions MOT Fail - Woodspeed
This is only just out of spec. If the car is not used hard sometimes then things gum up, the oil suffers fuel dilution, and the air filter can be a bit clogged if over 10k miles.
Usually a change of plugs, oil and oil filter, air filter, and take it out for an "Italian tune up" (a good hard drive using all the revs and sustained holding of high revs in 3rd) and a re-test (making sure the car is HOT when the emission test is done) would bring those figures back into line.
If not, then start looking further.
96 2.0 GTI Emissions MOT Fail - adam f
I gave it a full service a couple of weeks ago. Changed all filters and plugs and oil. I suppose the best thing will be to Get a diagnostics test done
96 2.0 GTI Emissions MOT Fail - yorkiebar
Have you got the full emissions readings?

CO, HC and Lambda.

It will be easier to comment when loooking at these all together.

I assume it failed on fast test and full test? Readings from both tests would help even more.

But if it failed on co only, then check for any (slight) leaks in the complete exhaust system.

96 2.0 GTI Emissions MOT Fail - adam f
First fast idle test

CO level = 0.61 % vol FAIL
HC level = 31 PPM PASS
Lambda = 1.009 PASS

Second fast idle test

CO level = 0.50 %vol FAIL
HC level = 19 PPM PASS
Lambda = 1.009 PASS

Natural idle test

Engine speed = 810 Rpm PASS
CO level = 0.50 %vol PASS
96 2.0 GTI Emissions MOT Fail - Javalin
Might be worth a bottle of ignition system cleaner too. Forte Advanced gsa formula or Forte ignition system cleaner maybe? The local garage (who also MOT) swear by it. I've used it on my 1.8 mk3 Golf (not for MOT purposes's though) and engine does seem a bit smoother.

I think (from memory) the high CO is rich running? Might be worth looking at the coolant temp sensor - though i'd assume it'd be rich at natural idle too. Maybe the air filter needs replacing - did you replace that already?

Cheers - let us know how you get on?

Edited by Javalin on 14/04/2009 at 13:54

96 2.0 GTI Emissions MOT Fail - adam f
Yes i replaced the air filter when i serviced the car. I have purchased a CAT and will get it fitted later this week.

I took the car to Kwik fit to 'borrow' there ramps and have a good look under the car. the CAT did not sound to good and when i gave it a bash, it sounded like the insides had started to break up.
There did not appear to be any holes/leaks in the exhaust system.

I will keep you posted
96 2.0 GTI Emissions MOT Fail - adam f
Car passed the MOT. It was the Catalytic converter that was at fault.