Hi everyone!

My car just failed its MOT for the second time on emissions

The CO level was 4.7% and the limit is 3.5%. I've done the obvious plugs and air filter but I think it must be something more serious. Are there any sensors anyone would recommend that I check?

Cheers, Giles

Not sensors, but have you checked the jetting of your carb? If you have got a good (not 15 years old) air filter in there, thats the only thing I can think it would be. Its a tad scary the first time, but pretty easy, basically only remove one at a time, to get to them you have to lift the top plate of the carb (3 screws iirc, although could be 5) Then they are the brass bits looking at you, that look like screws with holes.

They should all have numbers printed on them, else it is possible to judge their relative sizes by eye, although that involves having them all out. Numbers for which should be where are in Haynes, my car had a "specialist" fiddle with it when it didn't work, and completely muddled the jets up

hi, cheers for the suggestion but I have an injection engine so no carb.

^All the above.

If that fails, there's a screw in the air mass meter, the big black box thingy near the battery with a relay beside it. You'll need an allen key to adjust it. Wind it out to lean the idle mixture down.

Might be an idea to wait till the MOT time and then do it whilst the tester has his machine connected to it so you get it right.

If something else is wrong then you may not be able to get the CO down far enough to pass.....in which case we'll need to look at other things, but change the air filter and try the adjustment first.

is there a PulsAir system on this engine?? if so and it is plugged... unplug it!

No pulsair or EGR in the UK AFAIK

blast.. that would save you more than a full percent ...

Another vote for asking the MOT man nicely if you can twiddle the pot on the flappy paddle airflow meter when it's connected to his gas sniffer.

cheers

James

Gas it

Hi everyone, cheers for the response.

I'm going to book the MOT early next week and i'll try to persuade the mot man to let me adjust the airflow meter while it's hooked up. I've already leaned off the mixture a bit in case he won't let me. Any ideas how much I can reduce the mixture by? I have horrible visions of the allen bolt on the airflow meter shooting out if I loosen it too much. I gave it 10 turns anticlockwise and the engine note seemed the same.

I've also put a bottle of some sort of pre-mot liquid in the fuel tank. it's supposed to reduce emissions and clean the injectors. Can't hurt for a fiver. It was recommended by an ex mechanic friend.

could your lambda sensor be the problem? assuming it has one.

It wont have one

the bottle will hopefully get the injectors clean. It may not do much at all but it certainly won't do any harm

Erm, if the engine note didn't change at all then there's no danger of you having over done the leaning out. You'll hear it drop slightly even as it comes into the correct range for Mr. MOT, so I would think it won't be too lean.

Fuel antifreeze reduces emissions as it is basicly ethanol and ethanol tends to reduce CO level, 2 litres to full tank is maximum amount so if there is half tank 1 litre at maximum.

How is connections of temperature sensor wires at cylinder head? If there is bad connection or sensor is going out, then it can make mixture too rich and thus emissions shoot high up. I would check these before adjusting AMM.

SHE PASSED!!
Cheers for your help everyone. Bought myself another year with the old girl.