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[terry paget]

Petrol 2001 manual 2.2 saloon
Good on CO2 and HC but lambda reading varying from 1.16 to 1.036. The engine light comes on occasionally code 0420 emissions bank one. Omega 2.2s have 2 lambda sensors, I understand the first one does the measurement and the second is the German emission test sensor, not used in UK. My hunch is to change the first lambda sensor and submit car for retest, but I seek advice.

[aaronjb]

Someone can correct me if I'm wrong, but.. my logic would be:

If CO & HC are both right then the CAT is working and the mixture is right (HC would be high if the mixture was off, CO high if CAT failed), so if the only symptom is the lambda value at the end of the exhaust (as measured by the MOT) being wrong then that would imply an air leak into the exhaust after the O2 sensor.

FWIW, 1.16 is 17:1 which is very lean - I'd expect it to be running like a bag of spanners..

[frostbite]

I could be an air leak

Mine failed emissions on the first fast idle, then when it had heated up on the second run it passed

You should ask when there is a slot for a retest and get the exhaust as hot as you can for them to test again

I thought mot stations were allowed to take the vehicle for quick blast to heat them up on allocated road?

[Kevin Wood]

Agree with Aaron. Cat is working so there's plenty of heat in it, otherwise, it'd fail on HC or CO.

I would check the exhaust for air leaks, especially as it's a 2.2, and they suffer from both cracked intake manifolds and broken studs, and the flexy sections in the exhaust giving up.

If it all looks OK, a look at the live data to see what the fuel trims are up to would be good.

[dave-b]

My 3.0 elite failed on the same issue a few years ago, and it turned out be small perforations in the twin pipes before the rear box allowing air to be drawn in.

[terry paget]

Thanks to all for advice. I had managed to remove the first lambda sensor, always a challenge after 17 tears in place, it looks fine, so I shall replace it. I know I have one leak becasue it drips water when idling cold, I shall look and listen for more.

[frostbite]

I found my pin hole driving close to walls, could here it hiss on one side but not the other

[biggriffin]

Thanks to all for advice. I had managed to remove the first lambda sensor, always a challenge after 17 tears in place, it looks fine, so I shall replace it. I know I have one leak becasue it drips water when idling cold, I shall look and listen for more.

A lamda sensor either works or it doesn't, a visual inspection won't tell you anything,.

[terry paget]

Having repaired a small hole in central exhaust last night, I had a retest today. Same as yesterday, zero CO and 9ppm HCs, but lambda around 1.15. The mechanic from next door looked in, and observed that CO reading of zero is unusual and suggest weak running.

I am now advised to change the lambda sensor. Tell me if I am wrong; I believe the lambda sensor ahead of the catalyst is the one that matters. The sensor after the catalyst does nothing in the UK, it is there to be used in some European countries for thie MOT tests.

[Kevin Wood]

Yes, that's right. It'll be the pre-cat Lambda sensor if it is a sensor problem.

I'm not sure if they are the same on the 4 pot but you might be able to swap pre and post-cat sensors if they are, as a test. Then again, it means you've got to unscrew another sensor.

[terry paget]

changed the pre-cat lamda sensor, had MOT retest - no change. Tester suggested I change the plugs and plug stick. I doing so I discovered this yellow discoloration on 1 & 2 insulators, puzzling. I attach pic of plug stick of MOT failing car X807 alongside plug stick off Y118, Ben's 2.2. Plus all looked fine, though there was oil in no.4 plug hole. Tester thought he could detect slight misfire, blessed if I could, and i drove the car 200 miles 10 days ago.
https://www.dropbox.com/s/5e6qu9fw7t7h5du/plugs.jpg?dl=0

[Kevin Wood]

Yes, looks like it's had some oil or water contamination in the past, but, if it wasn't actually misfiring I don't think it will be an ignition problem, and if it was, HC would be sky high.

I would suggest getting some live data from it at this point. Without it, we're guessing.

[terry paget]

Yes, looks like it's had some oil or water contamination in the past, but, if it wasn't actually misfiring I don't think it will be an ignition problem, and if it was, HC would be sky high.

I would suggest getting some live data from it at this point. Without it, we're guessing.

Thanks. Sounds like good advice, so I need access to a Tech2 or something similar that can read live data.  And yet, some component has to be faulty somewhere. If not lambda sensor, or catalyst, nor leaking main exhaust, it's hard to think what else is left. MAF sensor? Temperature sensor? Cam or crank sensor? ECU?

Can anyone recommend a reasonably priced live data reading meter for an Omega?

[TheBoy]

Given the number of Omegas you look after, a Tech2 would be useful

[terry paget]

Given the number of Omegas you look after, a Tech2 would be useful

Fair comment. Car failed a retest yesterday, following change of plugs and coil stick, and unplugging the MAF sensor.I now wonder whether I have substituted a faulty lambda sensor with another faulty one.
But I thought Tech2s cost thousands of pounds, and there were now cheaper devices that did the same job. Not true?