MOT Exhaust Emissions Test - Lambda reading ?

[BillyNoMates]

Just had an MOT done and as my vehicle is a trusty 13 years old Volvo with the original CAT and 150,000+ miles, the emission test is always a worry.

It passed with no problems. But I am curious to know what the Lambda reading on the emission test means. I understand what the CO and HC readings mean.

Any experts out there willing to explain ?

[lebesset]

well the lambda sensor measures the oxygen in the exhaust gas and adjusts your fuelling accordingly ; but there is more than one variety ; what does it say is the reading?

[lebesset]

I could have put that better! the ECU takes the lambda reading and adjusts the fuelling !

[russell1701]

the lambda sensor reads all the gasses running out of your engine calculates them together and if the reading is outside the parameters usely 0.97 to 1.03 (optimale 1.0 ) it will then ask your ecu (electronic control unit ) to adjust the air fuel mix to compinsate.

all petrol vehicles after 1993 have to have a cat test for the current mot but any vehicles before this do not have to be cat tested even if they are fitted with a cat

[BillyNoMates]

The acceptable range according to the emmision test is 0.97 - 1.03 (no units specified). My reading was 1.01 so within range.

I understand how my Lambda probe works with the ECU but want to make more sense of the test out of curiosity. My Lambda probe is the heated type as it has 3 wires vs. two if that's any help.

[BillyNoMates]

Anyone ? Surely someone can give me some insight into this ?

[BillyNoMates]

Found the answer - if anyone's interested it's all to do with the air-fuel ratio.

The correct one being 14.7 : 1 which gives a Lamda reading of 1. If the mixture is weak the lambda reading goes up and if rich it goes down. The acceptable range is generally accepted to be 0.97 - 1.03 as per the MOT.

The feedback from the Lambda sensor to the ECU to adjust this ratio maximises the efficiency of the catalytic converter.