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[Sir Gingerlot]

I have a '96 2ltr 8v Omega with 167000 miles. It has run brilliantly for 5 years and still does. However I can not get it through the MOT due to excessive CO (Carbon Monoxide). The pass level is 0.3 and mine reads 0.6. Right, now for what I've tried.
1 x New non original CAT. (Still not sure this isn't the problem)
1x Lambada sensor
1 x Engine temp sensor
New air filter, plugs and good oil
It's been in Vauxhall and their computer cannot identify any faults.
I am going to sell it soon for another Omega but I need to get it through the MOT.

Any ideas, preferably cheap ones.

Thanks

Ong

[Kevin Wood]

What test is it failing?

You should have a test of CO, Lambda and HC at a fast idle (2500-3000 RPM) and also a CO test at natural idle. If you post the whole test figures it might point to something.

If it's at natural idle the Lambda sensor is normally out of the picture as it doesn't normally come into play until higher RPM. If it's idling happily and otherwise OK it does kinda point to the cat.

Does it run OK despite the emissions? No signs of a misfire?

Other things that might affect the emissions are the MAF sensor and the intake air temperature sensor (although I'd expect a fault code), air leaks around the induction and exhaust system and blocked breathers.

Also, be sure the get the cat nice and hot before the test. give it a bit of motorway cruising if possible.

Edited to say: It might be worth getting the fuel pressure checked and putting some injector cleaner through it. Fuel filter might also be worth a try although it would have to be seriously clogged to affect the emissions off load.

Kevin

[Marks DTM Calib]

Is the engine getting to temp.....stat not stuck open....ECU light on?

[Sir Gingerlot]

Thanks for the replies. To answer some questions.
1. The car runs brilliantly no misfire.
2. The CO in question is when its running at 3000 rpm.
3. The breathers have been cleaned out.
4. There is a slight exhaust leak where the downpipe meets the manifold. This can only be heard on first start-up and as soon as the metal expands it stops.

You guys seem to know your stuff. Thanks again.

Ong

[Gaffers]

This must be very frustrating for you, my thoughts are centering around the fuel mixture, it would seem you are running v rich.  You changed the CAT (was it new?) which would point to the air flow sensor?  Only if there is a major fault would it show a fault code, if it is faulty and giving the wrong reading it wouldnt show a fault code yet could affect the mixture.  How is your fuel consumption? Has it gone up since you first got it, do you know your typical mpg?  

After that I would be stuck for answers......

[TheBoy]

Thanks for the replies. To answer some questions.
1. The car runs brilliantly no misfire.
2. The CO in question is when its running at 3000 rpm.
3. The breathers have been cleaned out.
4. There is a slight exhaust leak where the downpipe meets the manifold. This can only be heard on first start-up and as soon as the metal expands it stops.

You guys seem to know your stuff. Thanks again.

Ong

Exhausts with holes in can upset lamda readings... ?

[Kevin Wood]

Exhausts with holes in can upset lamda readings... ?

Just what I was thinking, having mapped my "other car" on the road with a wideband Lambda sensor I can confirm that the slightest air leak will put the readings out.

Extra air in the exhaust will make the Lambda sensor read lean, which means the ECU compensates by richening the mixture. ECU doesn't see a problem as long as it isn't bad enough to send the compensation out of the limits allowed.

Given that you're presumably passing the CO test at idle I think this is a strong pointer. CO is out of limits during closed loop but OK open loop. I think that puts most of the rest of the system in the clear because, to a certain extent, problems with the MAF and other sensors would have thrown it off at idle.

I know the exhaust blow seems to go away at temperature but I'd be inclined to try and seal it. It's a cheap thing to try and I think it has a good chance of solving your problem.

Kevin

[Marks DTM Calib]

Best confirm its getting up to temp as well first..........