MOT Failed on emissions
Discussion
Failed with persistently high lambda reading. CO and HC were a bit high but passed.
Test 1
Test 2
There don't seem to be any exhaust leaks and according to the software both lambda sensors are switching between 02. and 1.0 volts. Any ideas what I can do to get it through?
Test 1
| Test | Value | Limit |
|---|---|---|
| CO | 0.143 | 0.3 |
| HC | 105 | 200 |
| Lambda | 1.044 | 0.97-1.03 |
Test 2
| Test | Value | Limit |
|---|---|---|
| CO | 0.292 | 0.3 |
| HC | 191 | 200 |
| Lambda | 1.037 | 0.97-1.03 |
There don't seem to be any exhaust leaks and according to the software both lambda sensors are switching between 02. and 1.0 volts. Any ideas what I can do to get it through?
We spent ages trying all sorts of rev ranges and both tail pipes and the above were the best figures we could get.
Reading up, it seems like high lambda means too much oxygen in the exhaust stream which would possibly indicate a bad joint (where I put the cats back on??) or possibly a leak in the exhaust manifold. I will have a go at reassembling the exhaust with some GunGum.
It will have to wait a couple of days though as I am at Brands Hatch watching the Group C cars and JonnyW in the Superleague this weekend
Reading up, it seems like high lambda means too much oxygen in the exhaust stream which would possibly indicate a bad joint (where I put the cats back on??) or possibly a leak in the exhaust manifold. I will have a go at reassembling the exhaust with some GunGum.
It will have to wait a couple of days though as I am at Brands Hatch watching the Group C cars and JonnyW in the Superleague this weekend
Gray_101 said:
What condition are your cats like ? if you hold them up to the light and look through them you should be able to see light through the honey comb, if not they have had it.
if there blocked it will never pass in a month of sundays.
The cats look ok - you can see through the honeycomb and they heat up fine when the engine is running. I dont think that they would account for the high lambda reading though if they are on their last legs it mighe explain why the HC is borderline.if there blocked it will never pass in a month of sundays.
High HC to me suggests incomplete combustion so potentially very slight missfires of some sort.
The High Lambda reading could well be a very slight air leak on any of the intake or exhaust system components.
It won't be the Cat to manifold joint as the Lambda Sensors are before this.
Was it the same result both sides or did they only check one?
The High Lambda reading could well be a very slight air leak on any of the intake or exhaust system components.
It won't be the Cat to manifold joint as the Lambda Sensors are before this.
Was it the same result both sides or did they only check one?
ridds said:
High HC to me suggests incomplete combustion so potentially very slight missfires of some sort.
The High Lambda reading could well be a very slight air leak on any of the intake or exhaust system components.
It won't be the Cat to manifold joint as the Lambda Sensors are before this.
Was it the same result both sides or did they only check one?
They checked both sides and there was almost no difference between them. I will be checking for cracked manifolds in the morning. My thinking was that an leak in the exhaust below the cars lambda sensors could mean that here was excess oxygen in the exhaust stream - hence the high lambda test. If the leak was before the car lamdba sensors would the ECU not compensate by running richer which would produce a lower lambda test, or would that just mean more unburnt fuel hence high HC? The High Lambda reading could well be a very slight air leak on any of the intake or exhaust system components.
It won't be the Cat to manifold joint as the Lambda Sensors are before this.
Was it the same result both sides or did they only check one?
neiljohnson said:
Your exhausts are probably flowing too well causing the slightly high reading (have seen this on quite a few cars with decent exhausts) get a heat proof glove and slightly block the exhaust exit with the probe in it should then go through 
Never heard anything like that. How can an exhaust flow too well at idle?ridds said:
neiljohnson said:
Your exhausts are probably flowing too well causing the slightly high reading (have seen this on quite a few cars with decent exhausts) get a heat proof glove and slightly block the exhaust exit with the probe in it should then go through
Never heard anything like that. How can an exhaust flow too well at idle?Lambda reading on the emission test is the oxygen content of the exhaust gas,if the other readings are ok its normally a hole in the exhaust allowing air to be drawn in (perhaps cracked manifolds/leaky joints in the system).Holding the revs up higher helps but the test should be taken between 2500 to 3000rpm.
Of course if the vehicle is fitted with an older engine (pre 1993 for example before cats were mandatory and the emission test is a basic 3.5% co at idle) the emissions are tested on the age of the engine not the age of the car,however you are expected to prove to the tester this is the case.
Of course if the vehicle is fitted with an older engine (pre 1993 for example before cats were mandatory and the emission test is a basic 3.5% co at idle) the emissions are tested on the age of the engine not the age of the car,however you are expected to prove to the tester this is the case.
Thanks for all the suggestions (and mails)
I have found and fixed a couple of leaky joints in the exhaust, though fortunately the manifolds don't seem to be cracked. I will put it in for my free retest this week and see if that has improved things.
Still a bit concerned that the high HC level would imply that it is running rich, but I haven't noticed a misfire and the ECU software seems happy with the AFR. The adaptives are -8 and -12 which seems reasonable.
I have found and fixed a couple of leaky joints in the exhaust, though fortunately the manifolds don't seem to be cracked. I will put it in for my free retest this week and see if that has improved things.
Still a bit concerned that the high HC level would imply that it is running rich, but I haven't noticed a misfire and the ECU software seems happy with the AFR. The adaptives are -8 and -12 which seems reasonable.
Edited by Tanguero on Monday 2nd August 00:43
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