Mk3 Golf failing MOT on emissions


Wrench Pro
VW Mk3 Golf 1.4
I recently got my beloved VW Mk3 Golf MOT'd, I was considering scrapping it and buying something else but we've got a lot of history togetherso wanted to keep her going.

Before The MOT I got 2 new tyres, tracking sorted and a whole new exhaust system because the Cat had gone (except manifold) fitted at Wilko Direct. (The cost of the down pipe and cat was only £100 including fitting, I've been told this is very cheap for a CAT, even for a non type approved one and may be the problem?)

I though she would pass easy now, it did on everything except the emissions!

It was passing the HC but failing the C02 giving reading of around 0.600% out of 0.200% and only just failing on the lambda.

Long story short, I've fitted a new lambda sensor, new air filter, new spark plugs, Forte fuel additive thrashed the car about for an hour to clear out the engine and warm her up and still failing on C02 (but only just passing the lambda now, still passing HC)

I went back to Wilko and they checked the exhaust for leaks and took the car to a garage that they use for another emissions test. Same problem again.
They ordered in a new CAT and fitted it incase the old one was faulty, still failing on C02!!!

I've been to a couple of independent garages and they've basically said that I should scrap it, although it's not worth any money I love the car and seems such a shame to scrap her when it runs absolutely fine and passed everything but the C02 emissions...

N.B. the exhaust is emitting a fair amount of white smoke but not at start up, only when the car has been running for a while and warmed up. I've got no loss of oil, no loss of coolant water and no gammy mayonnaise on either caps. I've cleaned the throttle body and the engine seems to be running fine...

It's done 107k miles so is getting on but was hoping for at least another year on the road...

Any help would be great!!! Thanks
The only Petrol engine fuel cleaner I recommend is BG44k - use it once a year and you'll keep your injectors clean and engine in top condition.

See the product description of BG44k here. It should perk up general performance and clean the valves and head nicely.

White smoke is usually caused by coolant but as there is no loss it's really strange.

Are you using the correct grade of oil in the car? Is it misfiring at all?
Hi obi_waynne

thanks for the reply!
Yeah it's so weird! No loss of water and no mayo anywhere. oil is correct and same I've always used, not missfiring at all, not that I can tell anyway. starts fine and runs fine.

ever so slight judder on the rev counter but it is very slight, probably ranging from 900rpm down to 850rpm every now and then.

Only things I can think of is a dodgy cheap CAT or an air leak somewhere.
Trying to think of small little things that could be wrong...
There is a very small hole in the oil sump pan caused by a rock but it must be like a pin hole because it loses almost no oil from it ever...

That and there seems to be sort of wooshing noise when accelerating heavy at around 300orpm?
Thanks again
Does the shooshing noise stop when you press the brake? If so it could be an air leak in the brake booster.
hmm, not tried that. If I was to keep my foot on the accelerator and brake at the same time should it stop it then?
Thanks again
Does it stop when you release the accelerator then?

Check for a split air hose if that is the case. Get someone to press the accelerator while you examine the engine under the bonnet! Make sure they don't put it in gear.
Yeah it stops when you take your foot off the pedal but only gradually as the revs come down, not instantly.
I laid on the floor earlier to listen as I was pressing the accelerator pedal with my hand and it seems like it's coming from around the CAT area. As if the fumes are having trouble passing the CAT or something...

Kind of hard to explain, sorry.

I've just plugged a little diagnostics VAG reader that I got through the post today and it's coming up with an O2 sensor low voltage reading...

Any ideas what that could entail? shouldn't be the lambda because it's a new one!
Could be a bad connection to the sensor or a bad earth somewhere. That would explain a lot though, as the car uses the O2 sensor reading to trim the fuelling.
I done a compression test today and the readings are -

Cylinder 1 Cylinder 2 Cylinder 3 Cylinder 4
Dry - 60psi 75psi 70psi 70psi
Wet - 75psi 85psi 75psi 76psi

Any thoughts on these readings?
They don't look too bad to me but cylinder 1 does look a tad low and cylinder 2 a tad high.

Was hoping these readings would give me a definite diagnosis but still puzzled by it all
Any help would be great!

They all seem a little low to me. Shouldn't they read around 85 - 135 for a petrol engine? I know there is a lot of variation between engines and I don't know much about the 1.4's in these.

Have you found anyone posting up their test results for this engine?
Only found one piece of info about the compression in the 1.4's and it said that it was at 150psi...
Waaaaaay higher than what I'm getting.

Could be weak valve springs,or burned valves.Have you checked your oil filler cap for excessive back pressure?
If it's your rings that are worn,check the engine breather for excessive back pressure.
Sounds like the old girl could be worn out.
Could be weak valve springs,or burned valves.Have you checked your oil filler cap for excessive back pressure?
If it's your rings that are worn,check the engine breather for excessive back pressure.
Sounds like the old girl could be worn out.
If you are desperate to keep the motor,try removing the air filter and loosening the intake pipe to give it more oxygen.
It could give you a slightly cleaner burn.Might just get you through the CO2 test
one thing I did notice is that when I've got the rocker cover off and I turn the engine via the timing belt it sounds as though there is air leaking from the valves next to the distro cap... tried putting some oil over the gaps to see if any air bubbles would appear but no joy. Could be a problem there?

Anyway, I'm half way through stripping the head off now so will hopefully find the cause ASAP!
Check your camshaft seals.I would be inclined to focus on the valve seats/guides and springs.
Look for smoke when you first start up,that's a sign of worn valve guides.
Check your head for warp,it can track compression to the water jacket,could be the reason for the white smoke.
Check the bores for ovality,if they are too far gone it's a rebore,new pistons and rings.
If your bores are ok,you can get the valve seats re-cut,and new valve springs.( there is a set height/length for the valve springs)
It might work out cheaper and quicker to replace the engine from a vehicle re- cycling yard.
Just so you guys know,
I replaced the head gasket and valve stem seals, put it all back together and I was buzzing on how well it went, started it up and now runs worse than before!!! I've bought a Mk4 Golf now so the old gal is off to the scrappers soon.

Thanks for the help everyone!
Similar threads

Similar threads

Please watch this on my YouTube channel & Subscribe.