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high lambda - MOT fail

Hi there,

My L reg 1.6 Primera has just failed the MOT on high lambda by the narrowest of margins.

1st attempt 1.048, 2nd attempt 1.032 (vs limit 1.030) I understand high lambda means too much oxygen in the exhaust.

CO is incrediby low at 0.005 (vs limit of 0.300) HC is also extremely low at 3 (vs limit of 200)

The tester said he thought there was the tiniest air leak between the middle and back exhaust sections, which seems to fit this problem from my Googling around. Naturally, I'll try to take care of that.

Please comment on these other ideas I found from Googling that might just nudge it down a touch.

  1. New air filter - I would have thought that would have made it worse due to leaning the mixture.

  1. Clean the plugs and close the gap.

  2. Use super unleaded fuel prior to the test. - Can't see why that might help.

  1. Remove and clean the oxygen sensor. I'm a bit frightened of damaging it if it is seized in.

My nightmare scenario is that on recently fitting a new radiator, the fitter thought there were some bubbles of combustion gas in the coolent and that a new head gasket and skim was in order. Naturally, I hate that idea, especially as it uses no coolent and does not contaminate the oil. He may of course be full of it. Could that be related to high lambda?

Thanks in advance.

Fred

Reply to
Primera guy
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If the tester found a leak in the exhaust system then this should be a fail anyway regardless of the emissions. However, as the exhaust system is under positive gas pressure a leak would usually allow the exhaust gases out rather than fresh air in (hence why it's a failure), so that shouldn't directly affect the emissions test result (I could easily be wrong though).

The above are both standard service procedures so are definitely high on the list of things to do if they haven't been done for a while. Not guaranteed to solve your problem though...

Getting them out can be fun, but even if you do there's not really anything you can do without damaging or affecting their operation. Replacement is often the best bet. My Rover 414i failed on emissions many years back (can't remember the exact results) and I asked the tester whether I should change the sensor or the cat. He said that as you should replace the sensor at the same time as the cat it would be worth replacing the sensor first to see if that alone works - if not then you replace the cat. I was happy as the sensor was much cheaper than the cat and in my case that's all that was needed!

More likely air trapped in the cooling system. If there's no other symptoms (e.g. overheating, white smoke, loss of coolant/oil, excessive cooling system pressure, etc) then I wouldn't suspect the H/G. If there is air trapped in the system, particularly around the cylinder head, then the variations in temperature *might* have an effect on the emissions result but I honestly couldn't say.

Darren

Reply to
Darren Jarvis

nope.

reason for rejection : a [1] major leak of exhaust gases from any part of the system. note: a minor exhaust leak from, for example, a connection joint or a pin hole , is not a reason for rejection.

[1] note the word major, you'd be surprised what would pass.
Reply to
reg

You are ;-) As has been mentioned, a small leak isn't a failure. However a small leak can very easily push the Lambda up too high. I'd sort that before attempting anything else.

John

Reply to
John Greystrong

However, as the exhaust system is under

Even when pipework is under positive pressure any leak present not only allows the pressurised gasses out but also creates a pathway for external gasses to come in even if they are at a lower pressure.

Andy

Reply to
Andrew

Update ! MOT now passed. Lambda dropped from 1.032 (fail) to 1.01 (pass) after remaking with new gasket the joint between middle and back exhaust sections. Charge £~30 with no retest fee (3 days later) ! I came away happy.

Thanks for the advise. This is a great newsgroup!

Reply to
Primera guy

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