MOT emissions failure

My GTI has just failed its MOT on account of the fact its exceeded the emissions restrictions level.

I have tried using Redex emissions reducer but to no effect.

Can anyone suggest where I should start to look for the reason for this?

Cheers

What age is the GTI, pass levels changed in 1986 (I think) and did it fail CO or Hydrocarbons, and by how much.

Unless it's a really late '92 GTI Cabrio with a catayst and digipants ECU its quite hard to get a GTI to fail as the limits are double/triple or more what a serviced and tuned engine should be producing.

What is your CO reading?

Old clogged air filter will increase emissions.

Can you get the garage to tune the car as you can adjust the mixture via a bolt in the metering head, you just need an Allen key and the car set up to a CO meter.

1.5% to 2% CO is where you want to be.

Many thanks for the helpful comments .

I attach the test results and you will see that the only failure was hyrdocarbons where my September 1986 GTI is turning out 1655ppm where the limit is 1200ppm. I had already adjusted the fuel metering unit to run as lean as possible so there is no scope there for an improvement.

Frankly I am at a loss as what to do now. All I can think of is to have the fuel metering unit reconditioned. Is that likely to help?

If it does not do I then have to assume that the piston rings are shot and the engine is burning oil?

Cheers

RogB

RogB said

Many thanks for the helpful comments .

I attach the test results and you will see that the only failure was hyrdocarbons where my September 1986 GTI is turning out 1655ppm where the limit is 1200ppm. I had already adjusted the fuel metering unit to run as lean as possible so there is no scope there for an improvement.

Frankly I am at a loss as what to do now. All I can think of is to have the fuel metering unit reconditioned. Is that likely to help?

If it does not do I then have to assume that the piston rings are shot and the engine is burning oil?

Cheers

RogB

CO is high, factory is 0.5-1.5% and as said above 1.5-2% seems to make them happy.

I had a similar problem on my GTI, the inlet manifold gasket leaked allow excess air in one of the cylinders making it too lean to ignite and pumped out the unburnt HCs. This was at idle only, when underway and higher revs the amount of air leaking in was too small to effect running.

Does it idle smoothly or roughly. Problems with the ignition (plugs, leads, timeing) could cause a similar problem.

I'd try and find an old school garage that knows their way around K-Jet and get it adjusted correctly

I'll second the above - mixture still looks high at 3.3%.
You can check for any air leaks with some carb cleaner - whilst the car is idling, spray it round where the inlet manifold meets the head. Any increase in idle will indicate an air leak.

Are you using super unleaded petrol?

Is the timing set for super unleaded?

CO way high, you need to bring it down then the HC will come down.

I expect you have blacken spark plugs, give them a good clean and how old is you ignition system, HT leads, spark plugs, rotor arm and dissy cap?

How did you adjust the fuel metering head?