92 Golf Mk3 - Failed MOT - High CO2

[Boonestone8]

Hi all, I have a 1992 Golf Mk 3 1.8, which keeps failing its MOT due to having a high CO2 emmission (6.44%, with the legal limit being 3.50%) when tested despite repeated attempts to sort the problem.

To try and sort it out the following work has been done recently:

Oil change
New plugs
Air filter
(brand) New Cat
New temp sensor
Replacement (secondhand) ECU

The car has only 94k on the clock and has VW main dealer history upto about 78K and seems to have been well cared for. The car starts first time and runs really well, but I'm now stumped (as well as nearly bankrupt!) as to what to look at to get it fixed once and for all. At the moment it's a German pavement ornament, so any help / suggestions would be greatly appreciated! :1zhelp:

[golf tdi 02]

just a sugestion put some redex fuel treatment in and go for a drive on a bypass for around 5 miles get it nice and warm then go for emmisions test

rich\

[Lex Luthor]

I am sure you mean high CO ????
From another website :

Basic fault finding for advanced emission test failures:
If a vehicle fails for high CO at idle and /or fast idle then.... if Lambda is too low, the mixture is too rich. This can be caused either by a misfire or by a faulty Lambda sensor. If it's running very rich, the 02 and HC will be higher than normal.
if it has a high Lambda and high 02 (0.5 to 1.5%), the "CAT" could be faulty. Before condemning it make sure its hot enough to work, the Lambda and other sensors are working OK and the exhaust downpipe hasn't got any leaks.
if the vehicle fails for high HC then ...if the CO passes, the vehicle is probably misfiring. Or if the CO fails and the Lambda reading is too low, the mixture is probably too rich and it may also be misfiring.
if the CO fails, the Lambda reading is high and the O2 reading is high (0.5 to 1.5%) the "CAT" could be faulty. Again check out the simple measures above before condemning it.
if the Lambda fails then...if its too high the Lambda sensor may be faulty, the mixture may be too weak or there may be a hole in the exhaust downpipe. If Lambda is too low the sensor may be faulty, the mixture may be rich or the vehicle may be misfiring.I am surprised no one has changed the lambda sensor (o2 sensor) ?
What are the figures from your failed emission test ?

[golf tdi 02]

Hi all, I have a 1992 Golf Mk 3 1.8, which keeps failing its MOT due to having a high CO2 emmission (6.44%, with the legal limit being 3.50%) when tested despite repeated attempts to sort the problem.

To try and sort it out the following work has been done recently:

Oil change
New plugs
Air filter
(brand) New Cat
New temp sensor
Replacement (secondhand) ECU

The car has only 94k on the clock and has VW main dealer history upto about 78K and seems to have been well cared for. The car starts first time and runs really well, but I'm now stumped (as well as nearly bankrupt!) as to what to look at to get it fixed once and for all. At the moment it's a German pavement ornament, so any help / suggestions would be greatly appreciated! :1zhelp:



i think the easy things are first port of call .
in the list above he has changed the cat ?