Failed MOT. Lambda?

[SalvadorP]

Car just failed MOT. Inspector said the lambda value was above what is supposed to be. He said it should be 1.05 max and it was 1.35 despite him testing several times.
He said the values at the exhaust are fine.

Can you help me make sense of this information? What can the 1.35 he mentioned be refering to?

EDIT: I did ask specifically and he said the value was always 1.35 the 3 times.

[SalvadorP]

No one? Please guys I need help

More info. I do have a known exhaust leak pre sensor, at the exhaust manifold but, because I had to go through the impport process, I basically did 3 MOTs in the last 12 months, one of them 3 months ago, so I know the lambda was right. And the manifold has had that leak since I bought the car. So it is unlikely to be that.

[classicswede]

Dont confuse the MOT lambda measurement with the cars lambda sensor.

The MOT is looking for lambda 1 (what the cars sensor sees as 0.47v) 1.35 mot lambda says its lean. To get any more idea would need to see the CO and HC's etc

MAF or air leak are fairly likely

[SalvadorP]

Originally Posted by classicswede

Dont confuse the MOT lambda measurement with the cars lambda sensor.

The MOT is looking for lambda 1 (what the cars sensor sees as 0.47v) 1.35 mot lambda says its lean. To get any more idea would need to see the CO and HC's etc

MAF or air leak are fairly likely

Why did he say it could be 1.05 at most then?
The guy did say that likely the sensor was bad.

If it's MAF, that's bad news. I can't afford a new maf right now.

[buick boy]

Sounds like the lambda sensor is knackered . If the CO & HC readings are within limits and the lambda is above 1.030 I would change the lambda sensor as a first and cheap option.

[SalvadorP]

Originally Posted by buick boy

Sounds like the lambda sensor is knackered . If the CO & HC readings are within limits and the lambda is above 1.030 I would change the lambda sensor as a first and cheap option.

He did say the values at the exhaust were alright.
I read that a consistent tested value tends to point towards a faulty sensor. Whilst a leak would be inconsistent and present different values in each try. He said he tried 3 times and he got the same result each time.

I'm looking into a bosch or ntk replacement to see if it solves this.

[Clan]

Originally Posted by SalvadorP

Car just failed MOT. Inspector said the lambda value was above what is supposed to be. He said it should be 1.05 max and it was 1.35 despite him testing several times.
He said the values at the exhaust are fine.

Can you help me make sense of this information? What can the 1.35 he mentioned be refering to?

EDIT: I did ask specifically and he said the value was always 1.35 the 3 times.

The lambda reading for MOT is 1 , (+ or - 0.3 ) your 1.35 figure suggests it is slightly rich.

He said the emissions at the exhaust were ok but didn't give any CO figure.

CO should be about 0.2% at 2000 rpm no load. and 0.3 % at idle.

[SalvadorP]

Originally Posted by Clan

The lambda reading for MOT is 1 , (+ or - 0.3 ) your 1.35 figure suggests it is slightly rich.

He said the emissions at the exhaust were ok but didn't give any CO figure.

CO should be about 0.2% at 2000 rpm no load. and 0.3 % at idle.

Correct, he did not give me the figures. He said/the paper says, the reason it failed was the lambda value, not the exhaust values. But I understand knowing those could help diagnose.

In your opinion could this be as simple as replacing the O2 sensor?

[classicswede]

you can check the lambda is functioning with a multi meter

[SalvadorP]

Originally Posted by classicswede

you can check the lambda is functioning with a multi meter

Yes. I have my multimeter at the construction site of a house I'm renovating and I'm down with covid. Hopefully this weekend I'll be up and runing and able to test it.

Speaking of testing. I did test my MAF a while ago and the values were high. I couldn't figure out why. Hopefully it's not connected to this. But I guess there is a possibility MAF was on its way out back then, just not as bad.